Showing papers in "Philosophical Transactions of the Royal Society B in 1979"

Structural and Quantitative Studies on the Normal C3H and Lurcher Mutant Mouse

Abstract: The cerebellum, the deep cerebellar nuclei, and the inferior olivary nucleus of the heterozygote Lurcher mutant mouse have been compared with the same structures in normal littermates. The comparison was made using light and electron microscopic methods for qualitative observations and light microscopic methods for quantitative observations. The study included the newborn period from 4 days of age up to 730 days, which is old age for a mouse. The cerebellum of the normal mouse is similar to that of many other species though apparently minor structural differences are seen. Amongst these was the similarity between the mouse climbing fibre and mossy fibre glomeruli which contrasts with the rat where they can be distinguished by the high density of synaptic vesicles and central cluster of mitochondria in the climbing fibres. In Golgi stained material the inferior olivary nucleus of the normal mouse showed cells with highly ramified dendrites and cells with simple dendrite patterns. In the adult Lurcher mouse the cerebellum is much smaller than is normal. There are no Purkinje cells and the internal granule cell layer is reduced in thickness and density. Examination of younger animals shows that Purkinje cells are present and that they undergo degeneration. In Golgi stained material from younger animals Purkinje cells often show more than one primary dendrite, sometimes as many as five, and somatic spines persist well beyond the first week of life. Cytoplasmic organelles often have a random orientation and the mitochondria are rounded rather like those seen in the nervous mutant. Granule cells in the adult Lurcher mutant are reduced in number and during the developmental period degenerative changes are seen. The Golgi cells and stellate cells are relatively normal and some cells, identified as basket cells, are seen. The inferior olivary nucleus is found with ease in the Lurcher mutant and is as extensive as in the normal mouse. However, in Golgi stained material only cells with highly ramified dendrites are seen. In addition the total number of neurons is reduced. It is possible that the neurons with a simple dendrite pattern have climbing fibres which pass only to the Purkinje cells. The deep cerebellar nuclei in the normal mouse cannot be separated easily into their three subdivisions, lateral, interpositus and medial. In the Lurcher mutant the neurons are of similar size to those of the normal mouse but they are crowded more closely together than is normal. In the Lurcher mutant as in the normal adult the neuronal cell bodies are covered with synapses and not with glial cells. Estimates of total cell numbers were made in order to obtain evidence about the time course of the development of the changes in structure and to make a detailed comparison between the normal mouse and the Lurcher mutant with respect to Purkinje cells, granule cells, olive neurons, and deep cerebellar nuclei neurons. In the normal mouse the mean number of Purkinje cells between 10 and 730 days was 177 000, s.d. $\pm$ 11 600, n = 12. The number of granule cells probably reached a peak at about 17 days. At 26 days post-natal the number estimated was 27 million and at 730 days 28 million. The mean number of olive neurons between 14 and 730 days post-natal was 32 700, s.d. $\pm$ 1900, n = 9; the mean number of deep cerebellar neurons counted at three adult ages was 17 600, s.d. $\pm$ 1800. In the adult the ratio of Purkinje cells to olive cells is ca. 5.4:1, of granule cells to Purkinje cells is ca. 170:1, of Purkinje cells to deep cerebellar nuclei neurons is ca. 10:1, and of olive neurons to deep cerebellar nuclei neurons is ca. 1.85:1. This last would chiefly be of interest if there are olive neurons projecting solely to deep cerebellar neurons. In the Lurcher mutant the number of Purkinje cells falls below normal from 8 days post-natally, reaches 10% of normal at 26 days and probably falls to zero at around 90 days. At this point such are the changes in the overall structure that confusion of Purkinje cells with Golgi cells may occur. At 4 days post-natal age the number of granule cells is smaller than normal by 25% and this difference increases with age to a reduction of ca. 90%. The number of olive cells is close to normal until 8 days of age, is only 60% of normal at 15 days when the highest number is reached, and is 25% of normal at 121 days. The deep cerebellar nuclei neuron numbers were the same as those in the normal. Included in the discussion is a detailed critical comparison of these results from the normal mouse with all previous estimates of cell numbers in the cerebellum. The lesion in Lurcher is compared with that found in the other mouse cerebellar mutants and with experimentally evoked lesions of the cerebellum. For the Lurcher mutant the tentative conclusion is that the primary lesion may arise in the Purkinje cells.

Pollution-induced changes in populations

Abstract: The effects of pollution by organic matter, oil or industrial waste on marine communities are remarkably similar. Diversity values fall, biomass and numbers of organisms initially rise and then fall as the pollution load is increased. Diversity indices are, however, insensitive to pollution-induced changes and have to be assessed subjectively. Departure from a log-normal distribution of individuals among species offers a sensitive and objective method of assessing perturbation effects on communities. Under severe pollution stress, the dominant species are those which have a flexible life-history ranging from direct development to a planktonic larva and the ability to undergo short-term genetic selection. Species having a somewhat less flexible life-history strategy show increased abundance under conditions of slight pollution. The increase in abundance of seven or eight neither rare nor common species, which gives the departure from a log-normal distribution, is suggested as being the most significant and the earliest detectable change caused by pollution in a community. Thus the presence of a species in a polluted area may be more a question of life-history strategy than the tolerance of adverse environmental conditions. If this hypothesis is correct, considerable doubt must be placed on the ecological relevance of data from toxicity tests.

The Evolution of Bird Coloration

Abstract: The aims in this paper are first to review theories of the evolution of bird coloration and, in some cases, partly revise and extend them, secondly to analyse the coloration of all the birds of a given geographical region using multiple regression, and thirdly on the basis of this analysis to evaluate the various theories. Theories . There have been many discussions of the selective forces acting on the coloration of birds and we review the major proposals in some detail. The earliest suggestion (Darwin 1871) was that the bright coloration of many male birds originated through sexual selection by female choice of the most exotic variants in male plumage. A conflicting view (Hingston 1933) is that brightness has an intimidatory effect on opponents, and that bright male coloration arose through sexual selection but largely due to its advantages against other males in disputes concerning mating access to females. Bird coloration has also been considered in terms of predation (see, for example, Cott 1964 a ). Some birds with bright plumage patterns are known to be unpalatable compared to cryptic species, and certain other patterns have been interpreted as adaptations to confuse predators. Bright colours may commonly be favoured when an individual is anyhow obvious (e.g. through activity) and where it represents an 9unprofitable’ prey for a predator. This interpretation may be particularly relevant to lekking among polygamous males. A special case of unprofitable prey may be ‘perception advertisement’, where an animal signals (by flash patterns or alarm calls) that it has seen a predator (or opponent). It is also possible that bright coloration may serve to deflect predators away from the nest site; this requires in many ways conditions opposite to those for the unprofitable prey solution. Finally, bird colorations can act as a variety of social signals other than threat. Analysis . The coloration of the 516 species of birds that breed and/ or winter in the Western Palaearctic was analysed by multiple regression. Seven regions of a bird’s body plus two areas of flash coloration were recognized and scored for colour on a cryptic/conspicuous scale. Five different age/sex/season categories were recognized and scored separately for each species. These dependent variables were each analysed with respect to 17 independent variables that reflect different aspects of the reproductive biology and ecology of the birds. The advantages and disadvantages of multiple regression as an analytical technique are discussed. Results . The analysis identifies associations between the reproductive biology and ecology of the birds and the coloration of the different regions of the body of the different age/sex/season classes. Apparent exceptions to these associations are also identified and discussed. A relatively large proportion of the associations made sense in terms of the theories presented and usually there was a strong implication that for any specific association one theory was more relevant than any of the others. The results indicate that by far the most potent selective pressures to have shaped bird coloration are those related to predation risk. A number of the theories make use of predation risk, each in a different way, and for most of them some support can be gained for their involvement in the evolution of bird coloration. Of all the theories, however, it is the unprofitable prey model that seems to account for the major part of the variation in bird coloration. By contrast, no clear evidence for the involvement of sexual selection in the evolution of bird coloration could be found. Indeed, many associations, such as that between sexual dimorphism and polygamy, were more readily explicable in terms of selection pressures due to predation risk than of sexual pressures. The suggestion that bird coloration is shaped by predation rather than by sexual selection in no way prevents the coloration, as it evolves, being incorporated within the species and sex recognition system. Conclusions . It is concluded that bird coloration has evolved almost entirely in response to predation-based selective pressures. Although plumage and coloration are involved in species and sex recognition systems, they have not evolved in response to sexual selection pressures. In species that are sexually dimorphic, the male is not brightly coloured as a result of female choice or male: male competition but because he represents a less profitable prey to a predator than the females and juveniles. We predict that brightly coloured birds will most often be found to suffer less from predation than will comparable more cryptic birds (though one of the predation-risk theories does allow the converse to be true).

A Marker Induction Mechanism for the Establishment of Ordered Neural Mappings: Its Application to the Retinotectal Problem

Abstract: This paper examines the idea that ordered patterns of nerve connections are set up by means of markers carried by the individual cells The case of the ordered retinotectal projection in amphibia and fishes is discussed in great detail It is suggested that retinotectal mappings are the result of two mechanisms acting in concert One mechanism induces a set of retinal markers into the tectum By this means, an initially haphazard pattern of synapses is transformed into a continuous or piece-wise continuous projection The other mechanism places the individual pieces of the map in the correct orientation The machinery necessary for this inductive scheme has been expressed in terms of a set of differential equations, which have been solved numerically for a number of cases Straightforward assumptions are made as to how markers are distributed in the retina; how they are induced into the tectum; and how the induced markers bring about alterations in the pattern of synaptic contacts A detailed physiological interpretation of the model is given The inductive mechanism has been formulated at the level of the individual synaptic interactions Therefore, it is possible to specify, in a given situation, not only the nature of the end state of the mapping but also how the mapping develops over time The role of the modes of growth of retina and tectum in shaping the developing projection becomes clear Since, on this model, the tectum is initially devoid of markers, there is an important difference between the development and the regeneration of ordered mappings In the development of duplicate maps from various types of compound-eyes, it is suggested that the tectum, rather than the retina, contains an abnormal distribution of markers An important parameter in these experiments, and also in the regeneration experiments where part-duplication has been found, is the range of interaction amongst the retinal cells It is suggested that the results of many of the regeneration experiments (including apparently contradictory ones) are manifestations of a conflict between the two alternative ways of specifying the orientation of the map: through the information carried by the markers previously induced into the tectum and through the orientation mechanism itself

Bioaccumulation of marine pollutants.

Abstract: Bioaccumulation of pollutants can occur from sea water, from suspended particles, from sediments and through food chains. The rate at which accumulation occurs in an organism depends not only on the availability of the pollutant but also on a whole range of biological, chemical and environmental factors. The ultimate level which is reached is governed by the ability of the organism to excrete the pollutant or, alternatively, store it. This latter course often leads to the attainment of very high concentrations and sometimes no equilibrium level is ever reached. Two particular topics which are considered are the biological amplification of pollutants along food chains and the development of tolerance which sometimes occurs.

Measurement of the responses of individuals to environmental stress and pollution: studies with bivalve molluscs

Abstract: Certain physiological differences between individuals in different populations of the mussel, Mytilus edulis, are described. In particular, the scope for growth differs in space and time and may be used to assess the animals' physiological condition. When the required measurements are made in the field, the rates of growth predicted from the physiological data agree well with observed rates of growth. An alternative approach utilizes mussels transplanted to various waters, with indices of condition then measured in the laboratory under standard conditions; an example of this approach is illustrated. Laboratory experiments are used to equate various levels of physiological condition with fecundity, in an attempt to equate physiological effects on the individual with likely population damage. A cytochemical index of stress is described, based on the latency of lysosomal enzymes; spatial variability in this index, and its relation with the scope for growth, are discussed. Finally, the results of some experiments on the effects of petroleum hydrocarbons on mussels are described and the presence of inducible activity of NADPH-dependent tetrazolium reductase in the blood cells is demonstrated. Certain considerations that apply in adopting similar measurements of biological effects of pollution in environmental monitoring programmes are discussed.

Flandrian sea level changes and vegetational history of the lower Thames estuary

Abstract: A biostratigraphic study, investigating the interleaved Flandrian biogenic and inorganic deposits of the lower Thames Estuary, has been carried out between central London and the Isle of Grain. The vegetational and environmental history, showing the relation of the biogenic deposits to former sea level has been deduced from pollen, diatom and other microfossil studies. Radiocarbon dating has been used to establish an objective chronology. From this evidence the height of relative sea level movements, seen in marine transgression and regression surfaces, have been determined. These are plotted against time to show the rate of relative sea level change and subsidence trends for the Thames Estuary and southern England. Diatom studies show the early importance of marine and brackish water influences, at the beginning of Flandrian sedimentation in the Thames. Pollen and macrofossil analyses demonstrate the strong local effects of the saltmarsh and fen environment upon the vegetational history. The rise of Alnus pollen is seen to occur before 8100 years B.P., probably reflecting local physiographic conditions and valley flooding consequent upon the rising sea level. Elements of the regional vegetation development are recorded however, with the Ulmus and Tilia pollen declines shown. Five regression phases (Tilbury I-V), represented by the biogenic deposits and four marine transgressions (Thames I-IV), together with the possible existence of a fifth (Thames V), are recognized. The relative sea level for mean high water mark of spring tides (m.h.w.s.t.) is shown to rise at about 8500 B.P. from -26.5 m O.D. to above present Ordnance Datum (Newlyn) by about 1750 years B.P. Relative sca level curves for the Thames during Flandrian times correlate well with the form and rate of relative sea level changes shown for northwest Europe. Plotting these graphs against each other has allowed subsidence trends to be shown. Within the Thames, possible differential downwarping of approximately 1.5 m has been identified between Crossness and Tilbury for the Flandrian. The regional trends of west to east and north to south down-warping are supported. The amount of subsidence for southeast England, formerly given as 6.1 m since 6500 B.P., is not confirmed. The figure for the Thames area relative to the Bristol Channel lies closer to 2-3 m since 7000 B.P., although rates of downwarping vary with the type of environment studied, making generalizations tenuous. Sea level only shows relative subsidence trends and is not as yet seen to provide an accurate fixed datum from which one can give precise figures for land subsidence.

Morphology of the Wings, Legs and Tail of Three Coniferous Forest Tits, The Goldcrest, and the Treecreeper in Relation to Locomotor Pattern and Feeding Station Selection

Abstract: Functional morphology of the wings, legs, and tail of Parus ater, P. montanus, P. cristatus, Regulus regulus , and Certhia familiaris is analysed and compared, and correlations are sought with locomotion pattern and feeding station selection. These species are treated together because they are sympatric, occur in the same habitat, and partly overlap in feeding station selection, as well as in food selection. Where possible, the selective advantage of a feature is judged in terms of the energy savings that it makes possible with the respective locomotion pattern. P. ater has relatively low weight, low wing loading and long wing span. It is adapted to slow flight and high manoeuvrability. P. montanus has high wing loading, relatively short wings and long tail. It is not well adapted to manoeuvrable flight, but more to a clinging and climbing behaviour. P. cristatus has the highest wing loading of the species. It has short and broad wings, and rather short tail in relation to the body size. It is not adapted to slow manoeuvrable flight. It hops about on the branches or ground to a greater extent than the other species. Further, by its mere size, it is more adapted to low temperatures than the other species. R. regulus and C. familiaris have the lowest wing loadings and shortest arm wings in relation to the total length of the wings. C. familiaris also has relatively long span. The longer the span the lower the induced power, which forms a big part of the power consumption in hovering. The induced power per unit body mass is lowest in C. familiaris (1.13 W kg -1 ), and lower in R. regulus (1.19 W kg -1 ) and P. ater (1.21 W kg -1 ) than in P. montanus (1.28 W kg-1 ) and P. cristatus (1.31 W kg -1 ). The ratio (length of hand wing) / (length of arm wing) is 3.0 and 2.9 in C. familiaris and R. regulus , respectively, and 2.4- 2.6 in the other species. The shorter the arm wing is in relation to the total length of the wing, the more proximally the main mass of the wing will be located, and the less the inertial power and inertial loads on the wing skeleton become. The inertial power is another power drain in hovering. Therefore, because of their low wing loading and short arm wings, R. regulus and C. familiaris are particularly well adapted to slow flight and to hovering. P. ater and R. regulus are partly migratory and, therefore, should benefit more by long wing span than the other species. In fact, P. ater has relatively long span while R. regulus has not. The relatively short span in R. regulus is probably an adaptation for manoeuvrability and practicability in the dense vegetation where it usually forages. As related to body size, C.familiaris has the shortest legs, longest tail and toes, and longest and most curved claws, features that are obvious adaptations to climbing locomotion. The reduction of the leg length in the course of adaptations for climbing has affected the tibiotarsus most and the femur least. It is especially important for the tibiotarsus to be short to minimize the muscle force needed for clinging on a vertical trunk, and also to shorten the legs with least loss of step length. The tail is used as support in climbing (although not during the latter part of the power stroke). The longer the tail is, the less the horizontal force between claw and bark becomes, and, hence, the less the energy expenditure during the power stroke in climbing. The three tits have almost the same relative leg length. R. regulus has the longest legs in relation to body size. P. ater, P. montanus and C.familiaris have relatively short tarsometatarsus. Further, P. ater and R. montanus have long muscle lever arm of the flexor of the tarsometatarsus. Both characters are adaptations for hanging under branches and/or for climbing. Birds with need of rapid leg movements should have a short lever arm for the flexor muscle of the tarsometatarsus. During foraging R. regulus, P. cristatus and C.familiaris use their legs more for hopping, which requires speed of leg movements, and less for hanging than do P. ater and P. montanus , and they also have shorter muscle lever arms than the latter two species. In C.familiaris the short tarsometatarsus thus is adapted for hanging whereas the short lever arm of the muscle force is not. When the bird is hanging under a perch with 45° flexion of the tarsometatarsus relative to the tibiotarsus, then the muscle force (of M. tibialis anticus) per unit body mass is about 36, 44, 45 and 54 % larger in R. regulus than in P. cristatus, P. ater, C.familiaris and P. montanus , respectively. The corresponding differences between P. cristatus and the three latter species are 6, 7 and 14%. A clustering process was used to illustrate more clearly the phenetic resemblances among the species regarding the morphology of the locomotor apparatuses. As regards the wing skeleton the tits form a group, and C.familiaris is more similar to the tits than to R. regulus . The wing-form phenogram shows that P. montanus and P. cristatus resemble each other most, that P. ater is intermediary between these tits and R. regulus , and that C. familrsis most similar to R. regulus . The phenogram based on the form of the leg and foot shows that the tits resemble each other most and that R. regulus and C. familiaris are rather unlike the tits and also very unlike each other. In the tits, the skeleton of the legs is more diverse than that of the wings, and seems to have been subjected to more divergent selection pressures than the wing skeleton. As regards aerial locomotion in the three tits, the adaptation to different niches, and hence to different flight patterns, have led to divergent evolution of the wing feathers rather than of the wing skeleton. The pattern for all five species together is most diverse in leg characters and wing form and least diverse in the wing skeleton.

Late Quaternary vegetational history of the Enga province of Upland Papua New Guinea

Abstract: Stratigraphies and pollen analyses are reported from three sites within 25 km east and west from Wabag in the highlands of Papua New Guinea, namely: Sirunki, 2500 m above sea level, 32000 to 1500 yr Inferred Ages; Inim, 2500 m above sea level, 10000 to 0 yr Inferred Ages; Birip, 1900 m above sea level, 2300 to 0 yr Inferred Ages. Events evidenced by these data are described against a time scale of Inferred Ages (I.A.) based on radiocarbon dates and stratigraphic considerations. The pollen analytical data from Sirunki are presented in terms of pollen recovery (deposition) rates as grains per square centimetre per year (grains cm $^{-2}$ a $^{-1}$ ) and their interpretation controlled by information about total pollen deposition rates and differential pollen production and transport at the present day. Around Sirunki, the composition of the vegetation before 27 500 I.A. is enigmatic, although almost certainly it was treeless. From then until 9000 I.A. subalpine and alpine conditions dominated except during two short periods when forest taxa grew in the catchment. Final afforestation began about 9000 I.A. but the composition of the forest did not stabilize until about 3000 years later. This relative stability was shortlived; soon after 5000 I.A. fluctuations in forest composition began. These fluctuations were associated with periodic changes in the proportion of forested to unforested land. The Inim data lead to conclusions generally compatible with those drawn from Sirunki. However, data from the two areas differ in detail, particularly in the later onset of change in the local forests about 2000 I.A. and its intensification, coeval with a diminution in forest area, after 500 I.A. The short record from Birip is dominated by seral changes on the crater wall itself but the main indicators of forest disturbance and unforested areas were already there at its beginning (2300 I.A.). It seems likely that general forest destruction began, or gained greater impetus, around Birip about 450 I.A. In the most general terms, the forest taxa, recorded by pollen analysis, have behaved consistently with their present distributions and ecological relationships throughout the last 30000 years. More detailed resolution, however, exposes many deviations from this generalization. The majority of taxa are usually associated in groups which vary in their composition repeatedly during a few thousand years, yet some of the taxa occasionally behave entirely individualistically. The establishment of forest broadly comparable with that growing around Sirunki today began about 9000 I.A., when the main components entered the catchment, but took about 2500 years to achieve balance and a repeated regeneration process. About 4500 I.A., the relationship between forest canopy trees and forest ephemerals changed from one explicable in terms of the latter's role in natural forest regeneration to one suggestive of the ephemerals' wide spread through the forest which could only have been achieved by degradation of the canopy. It is suggested that a rise in the Sirunki basin's water level and the destruction of the surrounding forest about 13500 I.A. may have been due to seismic activity. The failure of the forest to re-establish there until 9000 I.A. was perhaps due to continued earth movement and partially to climatic conditions. The vegetation record from Sirunki suggests that the mean annual temperature there was similar to that of today between 27 000 I.A. and 25 500 I.A. but fell irregularly thereafter until between 18 500 I.A. and 16 000 I.A. it was probably about 10 $^\circ$ C below present. The mean annual temperature rose rapidly after 16 000 I.A. and was within 1 $^\circ$ C of its present level by 13 500 I.A. The cold episode between 18 500 I.A. and 16 000 I.A. corresponds with the last glacial maximum at higher altitudes in New Guinea. Pollen analytical evidence of the altitude of the forest limit and Climap Project Members (1976) estimates of sea surface temperature at that time suggest a temperature lapse rate of about 8.5 $^\circ$ C per 1000 m altitude (compared with 5.8 $^\circ$ C at present), with a firn line kept high, as the geomorphological evidence demands, by low precipitation at high altitudes. In this coldest period the altitudinal forest limit was about 1500 m below its present level of 3800 m. There is some evidence to suggest that the highest altitude forests of that time may have been quite different from those of today, perhaps containing components of the lower mountain forest canopy as well as the plants of the present upper mountain forest. This implies that the upper mountain forest becomes a separate entity only during comparatively short excursions up the mountains during periods of relatively warm climate. The low altitude of the forest limit during the last major cold period and its subsequent rise through 1500 m must have had substantial repercussions on the composition of the forests at lower altitudes. Although there is no archaeological evidence, the pollen analytical data suggest human interference with the forests around Sirunki from about 4300 I.A., which for 1300 years involved clearing of the forest and the enhanced growth of ephemerals of forest and open-land. Subsequently, the forest remained generally degenerate and a new wave of clearing began about 2000 I.A. near both Sirunki and Inim which continued and intensified about 500 I.A. At the lower altitude of Birip, forests were already disturbed by the beginning of the pollen analytical record at about 2300 I.A.

The Primitive Cynodont Procynosuchus: Functional Anatomy of the Skull and Relationships

Abstract: An acetic acid prepared skull of the Upper Permian Karroo cynodont Procynosuchus delaharpeae Broom is described and an attempt is made to interpret its anatomy in functional terms. The dentition is adapted for an insectivorous habit with an incipient form of tooth occlusion between specific upper and lower postcanines. A specialized form of tooth replacement ensures that the posterior postcanine teeth remain functional for as long a period as possible. The adductor jaw musculature shows a masseter-like muscle between the zygomatic arch and the lateral surface of the angular bone, in addition to the large temporalis muscle which has invaded the lateral face of the coronoid process. The possibility of a monotreme-like detrahens muscle rather than a reptilian depressor mandibuli being present for jaw opening is suggested. The quadrate is moveable. The anatomy of the internal nares indicates that an arrangement of Jacobson’s organ and associated nerves, blood vessels and glands comparable to that of monotremes was present. Interpretations of the various foramina of the snout are presented. Fleshy lips were probably present but the skin over the dorsal surface of the snout was tightly applied. The venous system of the head involves reduction of the vena capitis lateralis and the development of emissary veins comparable in general to those of mammals. The brain is comparable in size and relative development of its parts to that of living primitive mammals. There was incipient development of a monotreme-like membranous anterior lamina of the prootic. The stapes had a mechanical role associated with the moveable quadrate, in addition to its sound conducting role. It may have been capable of transmitting low frequency sound from the lower jaw as well as higher frequency sound from a tympanic membrane. The more advanced, Triassic cynodonts form a monophyletic group, of which Procynosuchus is the sister-group. The archaic but highly specialized Dvinia is the sister-group of all other known cynodonts.

The Distribution, Variation and Origins of Pre-Devensian Tills in Eastern England

Abstract: In order to define quantitatively the lithological properties of the pre-Devensian tills in eastern England, calcium carbonate contents and mechanical compositions of 501 samples from 289 sites have been measured and heavy minerals counted in 102 of them. The results show that the tills may be divided into two groups: ( a ) a North Sea Drift group consisting of the Norwich Brickearth, the Cromer Tills, the Marly Drift of Cromer type and till members of the Contorted Drift, which is characterized by high sand and low opaque heavy mineral contents; and ( b ) a Lowestoft Till group including the Lowestoft Till of East Anglia, the Chalky Boulder Clay of the east Midlands, the Calcethorpe and Wragby Tills and the Lowestoft-type Marly Drift, which is characterized by low sand and high opaque values. The qualitative similarity of the mineral suites in the two groups, however, suggests a common origin in the North Sea basin. Automated contouring (SYMAP) has been used to represent the spatial distribution of till properties. These confirm that the Lowestoft Till group can be spatially separated from the North Sea Drift group, and divided into a Calcethorpe-Marly facies high in carbonates and lying astride the Wash, and a Lowestoft-Wragby facies with moderate but variable contents of calcium carbonate and occupying the rest of the region. Trend surface analysis has been applied to the Lowestoft Till group. At the first order level there are decreasing trends across the region, from northeast to southwest, in calcium carbonate, amphibole and epidote values and increasing trends in silt and clay. These are interpreted as showing a general movement from the North Sea of sandy and chalky material which became progressively modified by assimilation of Mesozoic clays. Higher order surfaces, particularly those of sand, garnet and amphibole values, point to the Wash as the focus of this glacial activity. It is proposed that the most vigorous stream of ice entered eastern England at this point, levelling the Cretaceous scarps and excavating the Jurassic clays of the Wash-Fens basin, and then fanned out into most of the region to deposit the clay-rich Lowestoft-Wragby facies. The Calcethorpe-Marly facies is considered to represent chalky North Sea material carried by marginal, and weaker, ice streams directly onto the Chalk of Lincolnshire and north Norfolk. The North Sea Drift group is believed to be the product of another ice body, penecontemporaneous with that depositing the Lowestoft group, which entered Norfolk from a more easterly part of the North Sea, incorporating sediments from this basin, but without crossing substantial outcrops of Jurassic or Lower Cretaceous formations or Tertiary clays. The Marly Drift includes a variant showing lithological affinities with both Lowestoft and Cromer Tills and which may be the product of complex interaction between the two ice sheets. All the tills studied seem most likely to be of Anglian age.

Middle Cambrian Polychaetes from the Burgess Shale of British Columbia

Abstract: The Burgess Shale (Middle Cambrian) polychaetes Canadia spinosa Walcott, Burgessochaeta setigera (Walcott) gen. nov. and Peronochaeta dubia (Walcott) gen. nov. are redescribed on the basis of Walcott's type specimens and on much additional material. Two new polychaetes Insolicorypha psygma gen. et sp. nov. and Stephenoscolex argutus gen. et sp. nov. are described. A poorly preserved specimen of unknown generic affinity is described as type A. The polychaetes are preserved as thin films that adhere to both sides of the split in the rock so that part and counterpart may be available. In C. spinosa, B. setigera and I. psygma, parts of the bodies such as the fascicles of setae are separated by thin layers of sediment that apparently seeped in during turbulent transport in turbidites or mudflows. The bodies therefore lie on two or more planes of microbedding and the factors that control exposure across a specimen are discussed. Aspects of the palaeoecology of the Burgess Shale are reviewed, including the distance the biota was transported prior to burial, the reasons for the exquisite preservation, and the effects of sedimentary compaction. C. spinosa was characterized by broad notosetae that extended across the dorsum, and large fascicles of neurosetae. Lobate branchiae were situated in the inter-ramal spaces. The prostomium bore a pair of elongate tentacles and the straight gut had an eversible unarmed proboscis. Several lines of evidence suggest that C. spinosa was an active benthonic swimmer. B. setigera was peculiar in possessing identical notosetae and neurosetae along the entire body. Long anterior tentacles, possibly of peristomial origin, may have been used in feeding. Indirect evidence indicates that B. setigera inhabited a burrow which it might have excavated with its proboscis. P. dubia may also have burrowed but it had uniramous parapodia bearing simple and acicular setae. The prostomium bore a pair of short appendages. I. psygma had extended neuropodia bearing cirri and elongate setae. The notopodia were reduced and cirri appear to have been wanting. The peculiar prostomium carried a pair of appendages. I. psygma is regarded as a pelagic polychaete. S. argutus possessed uniramous parapodia with simple stout setae. The bilobed prostomium bore at least one pair, and perhaps three pairs, of short appendages. Type A was the largest of the Burgess Shale polychaetes and had prominent setae on at least the anterior section of the body. Type A was a sediment eater but the feeding habits of the other polychaetes are uncertain. Particular attention is given to the influence of decay on the Burgess Shale polychaetes. To place the Burgess Shale polychaetes in some geological perspective other Cambrian worms, including a polychaete from the Spence Shale of Utah, are briefly redescribed and the late Precambrian (Ediacarian) worms Dickinsonia, Spriggina and Marywadea are assessed. Contrary to the findings of other workers, no convincing evidence for placing these latter worms in the polychaetes is forthcoming.

An experimental electron microscopic study of afferent connections to the primate motor and somatic sensory cortices.

Abstract: An experimental electron microscope (e.m.) study has been made of the termination of the afferent connections to the primate sensori-motor cortex. Following large, stereotaxically placed thalamic lesions, degeneration in the motor and somatic sensory cortices was studied at survival periods of 4 and 5 days. Degenerating thalamocortical terminals had asymmetric membrane specializations. In the motor cortex 89.5% made synapses on to dendritic spines, 9% on to dendritic shafts and 1.5% on to cell somata; in the somatic sensory area 89% made synapses on to spines, 11 % on to dendritic shafts and one example contacted a cell soma and a spine. A considerable number of the spines receiving synapses from degenerating thalamo-cortical terminals were traced to their parent dendrites and these were of the pyramidal type whereas the dendritic shafts and cell somata contacted by degenerating thalamo-cortical terminals were mostly of the large stellate type. Most of the thalamo-cortical degeneration in both cortical areas occurred in a dense band in the upper two thirds of layer IV and the lower half of layer III but a number of degenerating terminals were found deep to this; in the motor cortex a second, less dense, band of degeneration was present in the lower part of layer V and top of layer VI. Degenerating thalamo-cortical terminals making synapses on to dendritic shafts and cell somata were scattered through the deep half of the cortex and not concentrated in the dense band of degeneration and so formed a greater proportion of the degeneration in the deep layers, particularly in the motor cortex. Sections cut parallel to the pial surface in layer IV of the motor cortex showed a statistically significant association between the degenerating thalamocortical axon terminals and the bundles of apical dendrites present at this level. Degeneration of commissural fibres was studied after removal of the contralateral sensori-motor cortex. Degenerating terminals had asymmetric membrane specializations. In the motor cortex 96% made synapses on to dendritic spines, 3% contacted dendritic shafts and one example made an axosomatic synapse; in area 3 97% made synapses on to dendritic spines and 3% contacted dendritic shafts. A number of the spines receiving synapses from degenerating commissural axon terminals were traced to their parent dendrites and these were of the pyramidal type. The cell soma and the majority of the dendritic shafts receiving synapses from commissural terminals were of the large stellate type although some of the dendritic shafts were probably those of small stellate cells. In the motor cortex degenerating commissural axon terminals were found in all cortical layers but were relatively more dense in layer I, the upper part of layer III, the upper part of layer V and the lowest part of layer V with layer V I; in the somatic sensory cortex most degenerating commissural terminals were found in the superficial half of the cortex. Following lesions of the primary somatic sensory cortex (SI) or of area 6 of the premotor cortex, degenerating terminals making asymmetric synapses were found in the motor cortex. Of the terminals of association fibres from SI, 82% made synapses on to dendritic spines and 18% on to dendritic shafts; of those fibres from area 6, 76% made synapses on to dendritic spines and 24% on to dendritic shafts. For both these association fibre connections, a proportion of the dendritic shafts contacted were clearly identifiable as those of large stellate cells. Terminals of both association connections occurred in all cortical layers with no obvious concentrations at any particular depth.

A Study of the Axon Initial Segment and Proximal Axon of Neurons in the Primate Motor and Somatic Sensory Cortices

Abstract: The axon initial segments of pyramidal cells and large and small stellate cells in the primate sensori-motor cortex have a typical membrane undercoating and bundles of neurotubules. Those of pyramidal cells are directed towards the white matter whereas those of large and small stellate cells often run obliquely or towards the cortical surface and may be curved. Cisternal organs in these initial segments are related to symmetrical axon terminals, frequently coming into close apposition to the non-synaptic part of these terminals adjacent to the synapse between the axon terminal and initial segment. The dense plates of cisternal organs and the membrane undercoating of the initial segment are specifically stained by ethanolic phosphotungstic acid (ethanolic PTA). Pyramidal initial segments have spines which receive only symmetrical synapses, as do the shafts of the initial segments of each cell type. The full length of the initial segment was studied for fourteen pyramidal and two large stellate cells. All gave rise to myelinated axons although two pyramidal cells had lengths of unmyelinated axon between the initial segment and myelinated axon. One of these lengths of unmyelinated axon made an asymmetric synapse on to a dendrite just after losing its initial segment features. Quantitative analysis of these complete initial segments showed that whereas the diameter of the initial segment and the axon it gave rise to were approximately proportional to the size of the parent cell soma over a considerable range of cell diameters, the length of the initial segment appeared to be unrelated to either its diameter or the size of its parent soma but varied between 30 and 55 $\mu$ m apparently at random. Synapses were evenly distributed along the full length of the complete pyramidal initial segments, but the density of synapses on the initial segments of supragranular pyramids was about three times that on those of infragranular pyramids and cisternal organs were similarly more frequent in the initial segments of supragranular pyramids.

The Natural Regulation of Giant Tortoise Populations on Aldabra Atoll: Recruitment

Abstract: The reproductive ecology of the giant tortoise (Geochelone gigantea Schweigger) in three isolated populations was studied for 2 years on Aldabra Atoll. Density-dependent recruitment was demonstrated. Nest destruction in the low density area was dependent on the density of mature females providing a mechanism for regulating population size. Increases in annual rainfall and the resultant increase in food availability induced an increase in mean egg mass in the low density area (and thereby total hatchling production), whereas in the high density population mean clutch size, mean egg mass, total number of nests and total hatchling production all increased significantly. Large eggs produced large hatchlings which survived better during the first year than hatchlings from small eggs. Hatchling mortality was 94 and 81% in the first year in the high and low density populations respectively. Recruitment into the 5 year age class (after which predation is considered negligible) had almost ceased in the high density population compared with 0.44 per 100 breeding females per year in the low density population.

Biological variables, especially skeletal deformities in fish, for monitoring marine pollution.

Abstract: When considering principles for selection of indicators, ie biological variables, for monitoring marine pollution, it must be regarded as important to search for effects on the highest possible level of organization For a global monitoring programme there are, however, many practical limitations in the number of useful indicators The paper suggests skeletal deformities in fish as one possible indicator for this purpose in the future and gives a review on the occurrence, effects, causative factors and possible mechanisms of skeletal deformities in fish

The Nervous System of Loligo: V. The Vertical Lobe Complex

Abstract: The vertical lobe system is described in Loligo and Sepia . It receives inputs from the optic lobes, arms, mouth and skin receptors. These inputs are combined and passed through a system with several superimposed loops. The output includes large neurons reaching to control centres for the arms and mantle, which initiate movements of attack or retreat. Another part of the output passes back to the optic lobes. The vertical lobe system receives no input from the statocyst and has few connections with the basal lobes. The inferior frontal lobe allows interaction of impulses from the arms, mouth, mantle and skin. Its outputs pass to the buccal mass and arms and upwards to the superior frontal lobe. The latter has two parts comparable to those found in octopods, communicating with the vertical and subvertical lobes. The inferior and superior frontal lobes contain no microneurons with axons restricted to the lobe. The vertical lobes are strikingly different from those of octopods. They are not divided into lobules, they have many large cells and an extensive neuropil. Numerous microneurons, with axons not leaving the lobe, arise in the peripheral parts of the vertical lobe. The organization of the neuropil differs in the six lobes that make up the system. In the inferior frontal lobe all the inputs can influence any of the cells. In the superior frontal lobe the neuropil is layered and the topology of the optic lobes is probably preserved. In the vertical lobe large neurons are scattered throughout the neuropil among the processes of the microneurons. The subvertical and precommissural lobe neuropils allow many influences to converge on large output cells, which are also accompanied by microneurons.

Indian Ocean Giant Tortoises: Their Systematics and Island Adaptations

Abstract: Although wild populations are now confined to Aldabra, giant tortoises were originally present on many other Indian Ocean islands. All belong to the genus Geochelone but are referable to two distinct subgenera, Cylindraspis in the Mascarene islands and Aldabrachelys on Madagascar, Aldabra, the Seychelles and neighbouring islands. These are distinguishable by skull and nasal structure, degree of shell ankylosis and structure of the plastron. Neither group has obvious close relatives in other areas. Mascarene tortoises, which are completely extinct, comprised several species: G. vosmaeri and the smaller G. peltastes on Rodrigues, G. inepta and G. triserrata on Mauritius, and what should probably be called G. indica on Reunion. All the tortoises of Aldabra, the Seychelles and neighbouring islands seem to be referable to one species, G. gigantea which appears to have shown some geographical variation. Madagascar probably had two species, G. grandidieri and another usually named G. abrupta which may well be conspecific with G. gigantea and was possibly the source of the Aldabra populations. Many of the distinctive features of Indian Ocean and Galapagos giant tortoises are interpretable as adaptations to the peculiar environment of ocean islands, particularly their lack of big predators and competing herbivores.

Trace Elements in Soils and Crops

Abstract: To demonstrate the total amounts to be expected in soils, the ranges of contents of some 60 trace elements in ten representative Scottish arable surface soils are compared with ranges in soil-forming rocks and with crustal averages. It is, however, the amounts potentially available to plants rather than the total contents that are biologically significant. In temperate climates, trace element mobilization is greatest when weathering takes place under conditions of impeded pedological drainage, leading to the formation of gleyed soils. Mobilized trace elements occur in arable surface soils largely in adsorbed and chelated forms, which are available to plants to a greater or smaller extent depending on the prevailing soil parameters and on the element in question. Different species take up different amounts of trace elements: the proportions in the various plant parts vary with the element and the stage of growth. Information is required about the mobilization and uptake of many elements about which little is at present known but which may affect the functions of essential elements through inter-element interactions. Systematic soil surveys in which soils are mapped by associations related to parent material, with their series related to genetic soil types, provide a useful countrywide guide to trace element status.

The nervous system of Loligo IV. The peduncle and olfactory lobes

Abstract: The paired peduncle lobes lie at the sides of the brain behind the optic tracts, partly embedded in the optic lobes. Each lobe comprises two regions: the basal zone, with medium to large cell bodies and fibres, and the spine, with small cells and fibres. The spine is remarkable for the presence of two banks of numerous, fine parallel fibres. Some of these are the processes of cells intrinsic to the spine but others derive from cells in the ipsilateral optic lobe and statocyst and from the contralateral peduncle lobe. The array of longitudinally running fibres, with efferents passing across them at right angles, gives the lobe a cerebellum-like appearance. The peduncle lobe receives a visual input from second and third order cells in the optic lobe, and a ‘labyrinthine’ input from cells in the statocyst. The opticopeduncular fibres preserve precise topological relations. The lobe projects widely to motor areas, including the basal lobes and the oculomotor centre in the lateral pedal lobe. It also sends fibres back to the ipsilateral optic lobe. There is a conspicuous peduncle commissure. The organization of the peduncle lobes is similar to that in the three main basal lobes, and must be considered part of the basal lobe system. The functional interpretation of the lobe is that it provides a region where visual and ‘labyrinthine’ information can interact to regulate motor programs controlled by the optic lobe. This involves fine adjustments particularly of the mobile eyes but also of the fins, funnel, head and arms, so that the animal can track visually and smoothly follow moving targets. Such regulation could be achieved by precise timing in a feed forward situation and this may be the function of the parallel fibre system. The olfactory lobe lies close to the peduncle lobe but is distinct in its connections and cyto-architecture. Its input derives from the olfactory organ and the optic lobe and its main projection is to an area of the posterior basal region that lies close to the optic gland. The cells are large and some are almost certainly secretory. The neuropil lacks any obvious spatial regularities. The nature of the olfactory system remains enigmatic but it may be involved in reproduction.

A Qualitative and Quantitative Electron Microscopic Study of the Neurons in the Primate Motor and Somatic Sensory Cortices

Abstract: A study has been made of the neuronal somata in the motor and somatic sensory cortices of the monkey Pyramidal cells in the motor cortex are very similar to those described previously in sensory and parietal cortical areas The largest pyramidal cells in area 4, the Betz cells of layer V, are up to 50 $\mu$ m in transverse diameter Although basically resembling smaller pyramidal cells, the nucleus of a Betz cell often has a complex indentation and is smaller in relation to the overall size of the cell soma than is that of a smaller pyramid and the cytoplasm of Betz cells contains discrete clumps of endoplasmic reticulum As with other pyramidal cells, the synapses on to Betz cell somata are all of the symmetrical type Previous descriptions of stellate cells have been of cells receiving a high density of axosomatic synapses of both the asymmetric and symmetrical type Cells like this are found in both the motor and somatic sensory cortices and have been termed here large stellate cells In addition to their high density of axosomatic synapses, they have abundant cytoplasm full of organelles and usually contain stacks of endoplasmic reticulum Their dendrites similarly receive a high density of asymmetric and symmetrical synapses and contain prominent organelles and have a moderately varicose shape Large stellate cells occur predominantly in layer IV in area 3b but in the motor cortex they are also found commonly in the lower part of layer III and the upper part of layer V A third class of neuron has been described in both the motor and somatic sensory cortices and cells of this type have been termed small stellate cells These receive a low density of axosomatic synapses, but some of these are of the asymmetric type and they have sparse cytoplasm with few organelles They have a small rounded or fusiform soma, frequently have a dark nucleus, have no apical dendrite and their axon initial segments are thin and may be directed towards the cortical surface Most of the rounded small stellate cells occur in layer II whereas those with fusiform somata occur more in the deeper layers of the cortex A quantitative study was made of the cells in a strip of the same width running through the full depth of the cortex in both cortical areas The absolute numbers of cells in the strips of the motor and somatic sensory cortices were very similar as were the proportions of each type of neuron, 72% in cach area being pyramidal with 21% being small stellate and 7% large stellate in the motor cortex, and 23% small stellate and 5% large stellate in area 3b The quantitative study also provided evidence that large and small stellate cells form two distinct populations rather than being a continuum

Terrestrial Faunas and Habitats of Aldabra During the Late Pleistocene

Abstract: Far from being fixed and unchanging, the islands and land areas of the western Indian Ocean are in a dynamic state; the most important variable, apart from tectonic activity, has been the rise and fall of sea level as a consequence of late Pleistocene glacial advances and retreats. Geological studies at Aldabra show that there have been great variations in the land area of the atoll, the topography, and the height above sea level. Moreover, the land has been completely submerged on at least two occasions. Fossil tortoises, crocodiles, lizards, birds and snails illustrate, if fragmentarily, the pattern of colonization and extinction on the Atoll. Although the earliest terrestrial deposits represent vegetated sandy cay habitats colonized by crocodiles, iguanas, petrels, tortoises and snails, the later deposits indicate dissected rocky substrates with meagre soil formation and scrub vegetation more similar to present day Aldabra. However, both the lizard and snail faunas indicate that considerable faunal change has occurred.

The significance of low-density populations of the African armyworm Spodoptera exempta (Walk.)

Abstract: Mass emergences of moths from conspicuous gregarious-phase caterpillars in high densities are important sources of migrant moths, which are borne downwind to cause a progression of armyworm outbreaks northwards from Tanzania to Ethiopia, and southwards from Rhodesia to South Africa. This progression might possibly be checked by destroying outbreak caterpillars. The sources of moths which cause the first outbreaks before the progression starts are not known, and the possibility is examined that these come from scattered populations of solitary-phase caterpillars hidden at the bases of green grasses, where they are sometimes found at considerable density. Recent analyses of weather patterns on the estimated dates of arrival of the moths responsible for fourteen groups of outbreaks in Rhodesia suggest that outbreaks could often be caused by convergent windflow concentrating low-density moth populations from sources between Rhodesia and the Mozambique coast, and that these sources may persist for several months. A model is presented which attempts to relate the phase forms found in the field with the life system of the armyworm.

Tide pools of Carrigathorna and Barloge Creek

Abstract: An ecological account is given of tide pools on the remote promontory of Carrigathorna, formed of Devonian slates on edge, on the open Atlantic coast, and on a sheltered but otherwise similar slate reef nearby. Both sites are at the entrance to Lough Ine, County Cork, Republic of Ireland. In addition to its immediate ecological concern, this study is intended to provide a basis for comparison in the future, in case of climatic or other environmental change. The pools have been charted, and their levels and dimensions are specified. They range from 0.3 to 5 m in depth, and the largest holds over 100 m $^3$ . The highest studied are only replenished by wave-wash, and the lowest are never completely disconnected from the sea. As is generally recognized, various environmental conditions are subject to wider fluctuations in tide pools than in the sea. Examples are shown of diurnal and tidal changes in temperature and pH, and some readings of oxygen content and salinity are given. The deeper pools remain cool below even when their upper waters are warmed, and this is probably important in permitting the survival of Laminaria forest within them. Temperatures of over 25 $^\circ$ C were attained in high-level pools, and pools with much of the green alga Enteromorpha reached pH 10. Salinity ranged up to 40% in the highest pools, and oxygen tensions to nearly twice the saturation level. Five ecological facies characterized the tide pools of the open coast, from high level downwards: Enteromorpha scrub, smooth encrusting coralline alga scoured by limpets, Corallina scrub (extending into Laminaria forest as undergrowth), Laminaria forest, and Dictyota scrub (with other non-calcareous algae). Enteromorpha covered the bottoms of tide pools just above the highest tides, where the number of species present was small but in some cases the number of individuals very large. The extension of Enteromorpha to lower pools is largely prevented by limpets, themselves probably limited upwards by extreme conditions of temperature, pH, salinity etc. The extension of limpets in any numbers to lower pools is probably limited by the tough calcareous alga Corallina officinalis. Laminaria forest takes over in mid-tidal pools where the water is deep enough, and Corallina gives way at depth to Dictyota and other algae, possibly in relation to reduced illumination. The small Laminaria-eating limpet Patina pellucida reaches higher numbers in the shelter of tide pools than in the sublittoral Laminaria forest of the nearby open coast. The fauna associated with Corallina has been studied by means of 0.20 m x 0.15 m quadrats taken from many of the pools. Quantities of epiphytic coralline algae, spirorbid tube-worms, and epizoic Bryozoa have been assessed from 10 g aliquots of Corallina, and numbers of other species have been determined from the complete quadrat collections. Many progressive changes from high-tidal to low-tidal pools are described. One aberrant pool at Carrigathorna drains by slow leakage over the period of neap tides, and is occupied by a blanket of a blue-green alga (Lyngbya confervoides) populated by larvae of Halocladius fucicola (Diptera, Chironomidae). It is to be expected that L. confervoides (like other blue-green algae) can survive considerable desiccation. A pool on the more sheltered reef ('Urchin Reef') in the mouth of Barloge Creek contains much of the brown alga Cystoseira nodicaulis, which together with Corallina accommodates extremely large numbers of individuals of many invertebrate species. This sheltered pool, replenished on every tide, acts as a rich marine aquarium. Crevices in the bottom hold over 100 of the sea urchin Paracentrotus lividus, of which only a few specimens are found on the open coast. The hard slate probably does not allow this urchin to burrow, so that it probably cannot resist storms on the open coast. A large population exists in Lough Ine in shallow places where the water warms up in summer, and this population possibly provides larvae for settlement. The occurrence is recorded of 111 species of algae and of 198 species of animals in the tide pools.

The biomass, production and carrying capacity of giant tortoises on Aldabra

Abstract: The giant tortoise ( Geochelone gigantea (Schweigger)) population of Aldabra has varied greatly in numbers since the beginning of the present century. Recent estimates have shown that the population is composed of 150 466 ±s.e. 16 441 animals. Of this total, 60% are located in an area of 33.6 km 2 at the eastern end of Grande Terre. Animals composing the small population of 2000 tortoises on Malabar grow continuously, while those on Grande Terre only grow seasonally and are much smaller than their less numerous counterparts on Malabar. It is suggested that shade factors limit the time available for feeding in Grande Terre. Records of movement show that while some animals do move large distances 53% of the population are not relocated more than 500 m from their initial marking point. A mean annual rainfall of 941 mm would be expected to yield 1887 g m -2 a -1 (dry mass) of primary production, with a range of from 2337 to 4037 g m -2 a -1 . Tortoises of average mass (20-30 kg) consume 79 kg a -1 . Estimates of total consumption for areas with differing tortoise densities suggest that they would consume 11.3% at the eastern end of Grande Terre and 0.7% in the Pemphis scrub. Defecation records suggest that the gross assimilation efficiency of giant tortoises is about 50 %. The mean mass of tortoises on Aldabra are 21.7 kg on Grande Terre, 49.9 kg on Malabar and 51.3 kg on Picard. Standing crop biomasses derived from these weights are 35 387 kg km -2 on Grande Terre, 35 084 kg km -2 on Malabar and 25 342 kg km -2 on Picard. These biomass data are significantly higher than those achieved by large herbivores on mainland African wildlife ecosystems. By using data available on biomass mortality, P/B ratios (turnover times) of 0.042 for Grande Terre and 0.034 for Malabar are obtained. Annual production calculated from these ratios are 1486 kg km -2 a -1 for Grande Terre and 1193 kg km -2 a -1 for Malabar. The production efficiency of the giant tortoise population is about 2.1% which is in close agreement with figures obtained for other long-lived poikilotherms. Potential production for Grande Terre predicted from the mean rainfall only differs by 2.6% from that estimated. The eastern end of Grande Terre, however, exceeds this predicted figure by 61% and it is suggested that this is due to increased primary production induced by water available from the freshwater lens raised by spring tides. This phenomenon is similar to mainland African wildlife ecosystems fed by abundant ground water.

Geochemistry and health in the United Kingdom.

Abstract: Before the 1960s, comparisons between the distribution of trace elements in the environment and health in the United Kingdom were primarily confined to ad hoc studies in areas associated with particular agricultural disorders or with unusual human mortality or morbidity records More recently, increasing interest in the importance of trace elements in crop and animal production and in the hazards of environmental pollution have created a need for more systematic geochemical data Geochemical reconnaissance maps for England, Wales, Northern Ireland and parts of Scotland have demonstrated the extent of many known clinical trace element problems in agriculture and have also been valuable in delineating areas within which subclinical disorders may occur Their application to studies on the composition of soils, food crops and surface waters in relation to public health has proved encouraging Current knowledge and present investigations into environmental geochemistry and human health in the UK are reviewed, together with future research requirements

The Crag at Bramerton, Near Norwich, Norfolk

Abstract: Mollusc, foraminifer and pollen assemblages from sections at Bramerton, near Norwich, the type locality of the Norwich Crag, are described. It is shown that the marine sediments were deposited first under temperate conditions and later under colder conditions. The faunas and floras are compared with those elsewhere in the East Anglian crag and it is concluded that the temperate stage represented at Bramerton must be regarded as a new stage in the East Anglian Pleistocene succession, here named the Bramertonian, while the subsequent cold stage is equivalent to the Pre-Pastonian a substage of the Norfolk coast. It is likely that the Bramertonian stage also includes the Norwich Crag faunas of Suffolk at Chillesford, Aldeburgh, Thorpe Aldringham and Sizewell, together with the Westleton Beds. The first influx of quartz-quartzite-flint gravels in the Norwich area is shown to have occurred later than the deposition of the Bramertonian crag.

Palaeoecological Investigations at Ballynagilly, A Neolithic and Bronze Age Settlement in County Tyrone, Northern Ireland

Abstract: The Neolithic-Bronze Age occupation site at Ballynagilly was covered by blanket peat and surrounded by a deep mire. Stratigraphic investigations, pollen analysis and $^{14}$ C dating were used to investigate the history of the area and to relate this to the prehistoric occupations. A series of $^{14}$ C measurements from the mire were used to establish a deposition rate curve from which a time scale for the vegetational history was derived. This was also used to correlate the vegetation history with $^{14}$ C dated prehistoric occupations. Organic accumulation began in the deep mire about 8000 B.C. (the notation A.D./B.C. is used to denote a conventional $^{14}$ C age less 1950 years) and the earliest blanket peats began forming around 1000 B.C. In the early Littletonian Stage (Postglacial) a juniper phase gave way to birch and willow at *7450 B.C. (* is used to denote a date derived from the deposition rate curve). Until *6050 B.C. there was a period of low water level with a rich mire vegetation. Elm, oak, hazel and pine entered simultaneously at *6050 B.C. creating a dense forest cover. Alder first appeared at *4970 B.C. but did not expand until *3500 B.C. The mid-Postglacial was examined in detail and showed evidence of Neolithic forest clearance involving burning. Charcoal of pine, oak and hazel, $^{14}$ C dated to ca. 3200 B.C. was discovered. This date coincides with those for a Neolithic house and other associated features. The Neolithic clearance phase lasted some hundreds of years with periods of minor forest regeneration. During this phase different types of agriculture may have been used. A total recovery of the forest, albeit with a different composition, was deduced to have taken place before new clearance in Beaker times at ca. 2000 B.C. Somewhat before this, at *2200 B.C., the final decline of pine pollen occurred but was apparently unconnected with human activity. Heath began to develop at *1800 B.C. and increased in extent following Early Bronze Age clearance of scrub woodland at *1650 B.C. Various clearance episodes from this time through to *200 B.C. caused a further progressive deforestation. Brief regeneration after *200 B.C. was followed by indications of locally wetter conditions and renewed deforestation at A.D. *450. Despite some scrub regeneration around A.D. *800 continuing pressures on the woodland culminated in a open landscape by A.D. *1500.

Review of the problems

Abstract: Sublethal effects of pollution may be significant to survival of a stock of marine fish or even a species. Such effects sometimes lead to reproductive failure and have been identified so far only in freshwater systems. Atlantic salmon have disappeared from many streams in Europe and eastern North America, partly as a result of pollution in their freshwater spawning areas and in their estuarine nursing grounds. Reductions in populations of marine fishes due to pollution solely have not yet been demonstrated. However, Baltic Sea seals, where reproductive failure is apparently associated with high concentrations of DDT and polychlorinated biphenyl in the blubber, may have suffered a decline owing to the presence of these organochlorines. Sublethal effects of pollutants have been studied in the laboratory, essentially under four categories: (1) physiology (growth, swimming performance, respiration, circulation); (2) biochemistry/cell structure (blood chemistry, enzyme activity, endocrinology, histochemistry); (3) behaviour/neurophysiology; and (4) reproduction. Not all pollutants elicit meaningful responses in all categories, and a response is not always linear with pollutant concentration. For application to survival of populations the response has to be ultimately related to a healthy progression through a full life cycle, including successful reproduction. In recent time, physiological studies have moved into polluted marine environments with mobile laboratories having continuous sampling capability, to observe effects of pollutants in situ on marine organisms. The Controlled Ecosystem Pollution Experiment (Cepex) in Saanich Inlet, British Columbia, endeavours to investigate the effects of low concentrations of pollutants on marine organisms in large plastic silos having a slow replacement of water.

Experiments with Large Enclosed Ecosystems

Abstract: Three of the major advantages of enclosure experiments are that they ensure (1) that the same populations are sampled over a long period; (2) that populations of at least three trophic levels are initially enclosed in naturally occurring proportions and that they are self sustaining over a long experimental period; and (3) that replicate enclosed populations can be experimentally manipulated. There are two disadvantages which must be mentioned. These are (1) that vertical mixing, which may be reduced by as much as an order of magnitude compared to the open sea, will undoubtedly affect the sinking rates of phytoplankton and may influence the structure of the population; and (2) that as a general rule the larger and therefore more expensive the enclosures become, the more difficult it is to run sufficient replicates. An experiment is described in which 1 microgram Hg/l was added to two 95 m3 bags (3 mdiameter by 17 m deep) and the response of the pelagic population monitored over the following 20 days. A further 10 micrograms Hg/l was then added to each enclosure and the response measured for a further 20 days. The results indicated that: (i) inorganic mercury added to the water column is very rapidly transformed into 'bound' or 'non-reactive' mercury and that about 25% of the mercury added was recovered associated with the organic material settling to the bottom of the bags; (ii) the response of the biological population to 1 microgram Hg/l was very limited and in fact a transient reduction in photosynthetic carbon uptake per unit chlorophyll was the only noticeable effect and there were no changes in population size or structure that could be attributed to mercury; (iii) at 10 micrograms Hg/l the zooplankton population was reduced markedly and this did produce changes in the structure of both the zooplankton and phytoplankton populations. These results are similar to the results of a comparable experiment carried out in Vancouver Island (Cepex) and point to the conclusion that the levels of mercury found in surface waters around the coast of the U.K. (0.001--0.022 microgram Hg/l) are one or two orders of magnitude below the levels at which a response of the biological population can be demonstrated. The usefulness of large scale enclosed ecosystems for further pollution research is discussed and it is concluded that those facilities that provided a link between the water column and the sediments would be most useful since they would (1) enable estimates to be made of the flux rates of pollutants from the water column to the sediments; and (2) allow experiments to be carried out with the pollutant in contact with sediment in its natural form.