Showing papers in "Philosophical Transactions of the Royal Society B in 1971"

Simple memory: a theory for archicortex.

Abstract: It is proposed that the most important characteristic of archicortex is its ability to perform a simple kind of memorizing task. It is shown that rather general numerical constraints roughly determine the dimensions of memorizing models for the mammalian brain, and from these is derived a general model for archicortex.

The structure of the caudate nucleus of the cat: light and electron microscopy.

Abstract: The caudate nucleus of the cat appears to be homogeneous when examined with the light or electron microscope, except for a layer beneath the ependyma where there is a high concentration of glial cells and few neurons. In sections of brains stained with thionin the nerve cells in the caudate nucleus fall into three size groups: less than 8 $\mu m$ , 9 to 18 $\mu m$ , greater than 20 $\mu m$ . Examination of material impregnated with the Golgi technique shows that there are six cell types (one small, four medium and one large), and these are distinguishable on the basis of the size of the cell somata and the appearance and arrangement of their dendrites. One type of medium cell with many dendritic spines forms over 95% of the cell population. The large and one medium cell type are tentatively identified as the source of the efferent fibres of the nucleus. These efferent fibres and the axons of the remaining medium cell types have collateral branches. Three groups of possible afferent fibres have been identified, and these and the collateral branches of the intrinsic neurons form a dense plexus whose individual fibres cross dendrites rather than lie parallel to them. Six cell types may also be distinguished with the electron microscope, and four of these can be correlated directly with those seen in Golgi impregnated material. Several kinds of dendrites are present, the commonest having numerous spines. Fewer spines are present on other varieties of dendrite, and those dendrites which are varicose have no spines. Numerous fine, nonmyelinated axons are present.

Procedures for three-dimensional reconstruction of spherical viruses by Fourier synthesis from electron micrographs

Abstract: An account is given of a method which has been developed for computing three-dimensional density maps from transmission electron micrographs using Fourier transforms. The reconstructions objectively combine data from several different views of one or more particles. The application to negatively stained tomato bushy stunt virus is described in detail and the resulting reconstruction presented. Projections of the reconstruction in the appropriate directions agree well with images of the virus taken from micrographs.

The connexions of the striatum and globus pallidus: synthesis and speculation.

Abstract: Recent findings on the afferent and efferent connexions of the striatum (the caudate nucleus and putamen) and globus pallidus have been summarized in an orderly sequence. The striatum receives afferent fibres from three main sources, the cerebral cortex, the intralaminar nuclei of the thalamus and the midbrain; the major features of each of these pathways are outlined. The striatum sends efferent fibres to the globus pallidus and the substantia nigra, and the two segments of the globus pallidus in turn project upon the subthalamic nucleus and upon the thalamus and midbrain tegmentum. Through the thalamus the major influence of the striopallidum is upon the motor area of the cerebral cortex, and it is suggested that through the midbrain tegmentum there may also be a descending influence upon the spinal cord. These findings from light microscopical investigations are synthesized with observations made in electron microscopic studies of the striatum and globus pallidus. On the basis of present knowledge of their structure and connexions attention is drawn to several marked similarities between these parts of the basal ganglia and the cerebellum.

Fish gills: mechanisms of salt transfer in fresh water and sea water

Abstract: The teleostean gill is a multi-purpose organ, specialized for respiratory gas exchanges, clearance of waste products of nitrogenous metabolism and maintenance of acid-base and mineral balances. Structural studies reveal a complex epithelium. The 'chloride-cells are almost certainly the site of ion exchange in relation to salt balance. Functional studies show that the gill is responsible for the net absorption of Na $^+$ and Cl $^-$ occurring in fresh water and extrusion of these ions in sea water. In fresh water, a coupling between endogenous NH $^+\_4$ or H $^+$ and HCO $^-\_3$ excretion and Na $^+$ and Cl $^-$ absorption is observed. In sea water active Na $^+$ excretion is linked with K $^+$ absorption from the external medium. In parallel, active Cl $^-$ excretion occurs. The gill is also the site of Na $^+$ /Na $^+$ and Cl $^-$ /Cl $^-$ exchanges which involve 25 to 75% of the internal NaCl per hour. The relative importance of simple diffusion and exchange-diffusion in these exchanges is assessed. Biochemical studies reveal two enzymes playing important roles in the ionic pumps: carbonic anhydrase and Na-K activated ATPase. Studies involving transfer of euryhaline fishes from low to high salinity, show that the switch from fresh-water to seawater types of gill function is far from instantaneous. Synthesis or destruction of functional sites and renewal of specialized cells are involved. The role of external or internal NaCl concentration changes as stimuli for these 'inductive processes' and the endocrine control of these functional changes are briefly discussed.

Measurement and compensation of defocusing and aberrations by Fourier processing of electron micrographs

Abstract: The effects of defocusing and spherical aberration in the electron microscope image are most simply and directly displayed in the Fourier transform of the image. We have investigated the process of image formation by determining the changes in the transform of the image of a thin crystal of catalase, which has discrete diffraction maxima in the resolution range of 10 to 2.5 nm, as a function of defocusing. The changes in amplitude and phase of these diffraction maxima have been measured and compared with the predictions of a first-order theory of image formation. The theory is generally confirmed, and the transfer function of the microscope is completely determined by finding the relative contributions from phase and amplitude contrast. A 'true' maximum contrast image of the catalase crystal, compensated for the effects of defocusing, is reconstructed from the set of micrographs in the focal series. The relation of this compensated image to individual underfocused micrographs, and the use of underfocus contrast enhancement in conventional electron microscopy, are discussed. This approach and the experimental methods can be extended to high resolution in order to compensate for spherical aberration as well as defocusing. In as much as spherical aberration is the factor presently limiting the resolution of electron lenses, this could provide a considerable extension of the resolution of the electron microscope.

The site of termination of afferent fibres in the caudate nucleus

Abstract: An electron microscopic study has been made of the axon terminal degeneration in the caudate nucleus in the cat after lesions in either the cerebral cortex, the thalamus, the cerebral cortex and the thalamus, the midbrain or within the caudate nucleus. Degenerating axon terminals can be recognized after a survival period of 4 days as dark, shrunken profiles with indistinct vesicles. After shorter survival periods the degenerating terminals contain swollen vesicles and have pale cytoplasm. After lesions in all the above sites there is degeneration of fine myelinated and nonmyelinated fibres. The degenerating terminals of all the afferent fibres to the caudate nucleus have asymmetrical membrane thickenings and end mainly on dendritic spines with a small proportion in contact with peripheral dendrites; after damage of the cerebral cortex or thalamus a few of the degenerating terminals also end upon main stem dendrites and cell bodies. The projection from the ipsilateral cerebral cortex is greater than that from the thalamus, which in turn is heavier than that from the contralateral cortex or midbrain. After lesions within the caudate nucleus degenerating terminals with symmetrical membrane thickenings are found in a region extending approximately 450 $\mu m$ from the damaged part of the nucleus. These terminals make contact with nerve cell somata, main stein and peripheral dendrites and the initial segments of axons. After such a lesion of the caudate nucleus degenerating axon terminals with symmetrical membrane thickenings are also seen in the globus pallidus and the substantia nigra.

The termination of fibres from the cerebral cortex and thalamus upon dendritic spines in the caudate nucleus: a study with the Golgi method.

Abstract: The termination of fibres from the cerebral cortex and thalamus upon the dendritic spines of the medium spiny cell of the caudate nucleus has been studied with the Golgi method. Lesions were placed in the cerebral cortex, thalamus or cerebral cortex and thalamus of adult cats and kittens. After survival periods of between 6 and 52 weeks the animals were perfused with a mixture of formaldehyde and glutaraldehyde and the caudate nuclei impregnated by a Golgi technique. The distribution of spines along the dendrites of the medium spiny cell was determined in normal material by counting them over 20 $\mu m$ lengths of the dendrites, and was compared with their number and distribution after the various lesions. The density of spines on the dendrites varies with the distance from the cell body. The first 20 $\mu m$ length of dendrite is spine free, but thereafter the number increases to a peak between 60 and 80 $\mu m$ from the cell body after which the number per 20 $\mu m$ length decreases. The distribution pattern does not alter after any of the lesions, although the overall number of spines decreases. The decrease after lesions in the cerebral cortex or thalamus is the same, and after a combined lesion of thalamus and cortex is twice as great indicating that the fibres from both these regions end upon spines of the same cells. Statistical analysis shows that these results are significant.

Axoplasmic Transport (with Particular Respect to Adrenergic Neurons)

Abstract: The article presents a review and summary on the development of studies in the field of axoplasmic transport in non-adrenergic and adrenergic neurons. Results obtained by, for example, histochemical, biochemical, electronmicroscopical, autoradiographical and radiological studies are discussed. Two main types of axoplasmic transport appear to operate in neurons; the slow axonal flow of 1 to 2 mm/day, and the fast transport exceeding 100 mm/day. However, also intermediary rates have been observed. The influence of nerve activity and drugs on axoplasmic transport is discussed, in relation to the possible mechanisms for axoplasmic transport which may operate in the neuron.

Freeze-etching studies of membrane structure.

Abstract: Thin sections of biological membranes examined by electron microscopy appear as two dark lines separated by a lighter space. This observation, first made in the 1950s, has been interpreted as confirmation of the Danielli-Davson model of the biological membrane (Robertson 1959) . Proponents of this interpretation have equated the dark lines to proteins and other polar groups in the membrane and the intervening light space to the lipid fatty acids (Stoeckenius 1960) . However, it has become clear that other interpretations are possible (Korn 1966; Branton & Park 1968) and that the electron microscope observations do not in fact prove the validity of any one molecular model of the biological membrane (Stoeckenius & Engelman 1969). During the last few years a number of biochemical and physical probes have given us more direct information regarding the composition and molecular configurations within biological membranes.

The Synaptic Organization of the Caudate Nucleus

Abstract: The synaptic organization of the caudate nucleus appears to be homogeneous with no specialized groupings of axon terminals and postsynaptic profiles. The nerve terminals in the caudate nucleus fall into two size groups, one about 1 fim in diameter and the other about 5 /itn diameter. The smaller size group, which comprises the majority of terminals, may be subdivided into three varieties on the basis of vesicle morphology and the type of membrane thickening. Most contain round, 45 nm diameter vesicles and are associated with asymmetrical membrane thickenings. Others contain 48 nm diameter, polymorphic vesicles, which become flat in material washed in cacodylate buffer, and are associated with symmetrical membrane thickenings. A few other terminals with symmetrical membrane thickenings contain flat 42 nm vesicles. The large terminals contain round 45 nm diameter vesicles and have asymmetrical membrane thickenings. Axon terminals with asymmetrical membrane thickenings are found most frequently in contact with dendritic spines, but also with dendritic shafts and cell somata. Terminals with symmetrical membrane thickenings contact dendritic shafts and cell somata, and occasionally dendritic spines with which a terminal with asymmetrical thickenings is also making contact. The two types of terminal with symmetrical contact regions also form synapses onto the initial segments of axons. It is probable that such contact regions are invariably associated with cisternal organs in the initial segments. Serial synapses are found occasionally.

Recent Progress in the Freeze-Etching Technique

Abstract: The freeze-etching technique must be improved if structures at the molecular size level are to be seen. The limitations of the technique are discussed here together with the progress made in alleviating them. The vitrification of living specimens is limited by the fact that very high freezing rates are needed. The critical freezing rate can be lowered on the one hand by the introduction of antifreeze agents, on the other hand by the application of high hydrostatic pressure. The fracture process may cause structural distortions in the fracture face of the frozen specimen. The 'double-replica' method allows one to evaluate such artefacts and provides an insight into the way that membranes split. During etching there exists the danger of contaminating the fracture faces with condensable gases. Because of specimen temperatures below -110 $^\circ$ C, special care has to be taken in eliminating water vapour from the high vacuum. An improvement in coating freeze-etched specimens has resulted from the application of electron guns for evaporation of the highest melting-point metals. If heat transfer from gun to specimen is reduced to a minimum, Pt, Ir, Ta, W and C can be used for shadow casting. Best results are obtained with Pt-C and Ta-W. With the help of decoration effects Pt-C shadow castings give the most information about the fine structural details of the specimen.

Synaptic Organization of Cone Cells in the Turtle Retina

Abstract: The intercellular junctions of cone pedicles in the turtle retina were studied electronmicroscopically in tissue prepared by conventional techniques or impregnated by the method of Golgi. Dendritic branchlets of bipolar cells make specialized contacts with the basal surface of the pedicles. Processes ending laterally to wedge-shaped projections (synaptic ridges) of the pedicles probably belong always to horizontal cells, and make proximal and distal (to the synaptic ridges) junctions with the pedicles. Processes ending opposite the apex of the synaptic ridges are engaged also in two kinds of specialized contacts, termed apical and distal junctions. Basal processes of the cone pedicles make specialized contacts with adjacent pedicles, and with unidentified processes at the outer plexiform layer; their endings abut upon horizontal cell processes lodged within the pedicles of other cone cells.

On the Significance of Cross-Bridges Between Microtubules and Synaptic Vesicles

Abstract: Observations on the fine structure of synaptic and non-synaptic axoplasm in the spinal cord of the lamprey ammocoete (Petromyzon marinus) are described. Previous studies on this material revealed a close association between spherical vesicles and axoplasmic microtubules near central synapses, and observations were consistent with the suggestion that synaptic vesicles become detached from oriented microtubules in the focal clusters adjoining the presynaptic membrane across which transmitter release takes place. These observations have been extended to include axons containing non-spherical or ellipsoidal vesicles-possibly containing a transmitter chemically and functionally distinct from that in spherical synaptic vesicles. Structural cross-bridges between both microtubules and vesicle populations are now described; these are found not only in the vesicle concentrations bordering synaptic foci, but also in non-synaptic axoplasmic regions where sparsely distributed vesicles are found in association with microtubules. It is suggested that the bridging between vesicles and microtubules may reflect a mechanism for transport of the former-a possibility in accord with cumulative evidence of involvement of microtubules in rapid intracellular translocation in a variety of cells. It is proposed that arrival of excitation at a synaptic site is not only coupled with transmitter release across the axon plasma membrane, but that events at the cell membrane may in turn be coupled with a means of supplying vesicles to the synaptic locus. This hypothesis suggests that the synapse may rely on distant parts of the neuron, perhaps including the cell body, for materials involved in synaptic transmission.

The Holonematidae (Placoderm Fishes), A Review Based on New Specimens of Holonema from the Upper Devonian of Western Australia

Abstract: A new species of the placoderm fish Holonema is described from the Frasnian of Western Australia as H. westolli. A detailed account of the head and trunk shields is given; the palatoquadrate, opercular cartilage and gnathals are also described and receive special attention in view of the interest that attaches to these structures. Restorations of the armour are given in connexion with a discussion of the possible mode of life, and its convergent resemblance to antiarchs is noted. In a section on comparative morphology, some specimens of Arctolepis decipiens from Spitsbergen are partly redescribed; the variation in the dermal bones of the snout in Holonema westolli is analysed with respect to their possible ontogeny; and the structure of the nasal capsules and nasal openings in arthrodires is discussed, with the result that the usual elasmobranch model used in their interpretation is discarded; three possible interpretations of the snout in Holonema are proposed and one is tentatively accepted after a discussion of the available evidence, although it implies that some of the normal morphological relationships in the arthrodire snout have been seriously modified. The comparative morphology of the laterallines of the cheek and flank is considered, as well as of the jaw apparatus and gill cover. This last discussion is summarized in a general account of jaw suspension in placoderms. In a review of the family Holonematidae, the type and all referred genera (Holonema, Deirosteus, Rhenonema, Gyroplacosteus, Megaloplax, Deveonema) are tentatively defined, although the available information is not fully adequate for this purpose, and all named species and recent records are considered. The poorly known genera Aspidichthys, Glyptaspis, Groenlandaspis, Grazosteus, Tropidosteus and Arctonema, are excluded from the family. New material is described from Germany, Belgium and Scotland as Holonema spp. Throughout this review Holonema westolli is used as a standard of comparison rather than the poorly known type species H. rugosum. Finally the relationships and classification of the holonematids are considered. It is concluded that they are arthrodires at the advanced coccosteomorph level of organization, phylogenetically equally distinct from all other brachythoracids, and it is recommended that the Brachythoraci should be divided into the collateral taxa Holonematei and Eubrachythoracei, the former with the single family Holonematidae.

Summing up: some implications of the neuron as a secreting cell.

Abstract: ‘Believing that the nervous system is something more than a mere system of conducting paths, I formed the hypothesis that nerve cells are true secreting cells, and act upon one another and upon the cells of other organs by the passage of a chemical substance of the nature of a ferment or proferment’ (Scott 1905). ‘The most striking morphological feature of the neuron is the tremendous accumulation within its cytoplasm of small granules associated with a well developed endoplasmic reticulum. The same type of association is found in the ergastoplasm of glandular cells... cells which sustain an intense protein production. In the nerve this activity is implicit in chromatolysis and to certain types of generalized stress. The rapid regeneration of axons and the peculiar damming up of axoplasm proximal to a ligature are also reflexions of a continuous and rapid protein synthesis in the perikaryon.... The fact that the structure of the Nissl substance is the same as that of the ergastoplasm in glandular cells means that future analysis... in such readily available cells as those of the pancreas and liver can be profitably applied to the nerve cell’ (Palay & Palade 1955). ‘Neurosecretion should not perhaps be used as a term to describe only the histochemically demonstrable secretory processes of nerves such as those of the hypothalamo-pituitary system. The analogies are sufficient to indicate that similar processes are involved in the production, transport and secretion of acetylcholine from other nerve endings. So these, too, may also be called neurosecretory nerves’ (Hebb 1959). ‘All neurons have a secretory function by which active substances are synthesized and released. Secretion may act over a short distance on specific chemical receptors or on distant receptors by way of the blood stream. Intermediary examples are the adrenergic neuro-effectors ending on smooth muscle. Neurosecretion may be produced all along the neuron or at the nerve endings. In all cases, it is stored within a membrane in vesicles which represent multimolecular quantal units of neurosecretion’ (De Robertis 1964).

Optical Diffraction Studies of Myofibrillar Structure

Abstract: We have used the techniques of optical diffraction and optical filtering to study electron micrographs of myofibrils and of paracrystals of myofibrillar proteins. The optical diffraction patterns provide information about periodic structure in the micrographs, and sometimes may reveal periodicities not apparent to the eye. We compare the optical diffraction patterns with the X-ray diffraction patterns obtained from living muscle, and this comparison can assist our interpretation of both the X-ray diffraction patterns and the electron micrographs. The optical diffractometer we have used is essentially similar to those described by Taylor & Lipson (1964), and by Klug & DeRosier (1966). The apparatus incorporates several refinements to facilitate operation. The recombining lens has a focal length, f , of about 1 m, and is placed so that the recombined image is formed at 2 f and has the same size as the subject. The diffraction subjects are not usually the electron micrographs themselves but copies on film. The film is of more uniform optical thickness than the glass electron micrograph, and is less fragile. Moreover, a set of films of varying contrast can be made from one micrograph.

The Growth, Ecology and Population Structure of Giant Tortoises on Aldabra

Abstract: The giant tortoise of Aldabra, Geochelone gigantea, shows quite marked changes in proportions with age, although during growth the relations between the length of the carapace and various measurements of the plastron and scutes involve not only strong but also weak allometry. Certain scutes show a predisposition to split during growth. Accidental damage to the carapace is frequent. Males reach over 100 cm in carapace length but females are smaller, up to 80 cm. There is no segregation between the sexes in any single measurement investigated, except among the very largest animals. A general appraisal of carapace and tail shape is sufficient to sex only animals above 60 cm in carapace length. The number of annuli on each scute corresponds to the number of years of age at least up to the formation of the tenth to fifteenth annulus. A general assessment of the pattern of growth is made by plotting body measurements against number of annuli. Growth curves of individual tortoises are reconstructed by relating measurements of successively formed annuli to age. Growth rate is recorded by plotting the difference between successive pairs of annulus measurements against age. The growth rate of ageable tortoises varies between local populations on South Island and between populations of South and Middle Island. Growth rate declines with age, reaching asymptotes at mean values of between 20 and 30 years. Some individuals exhibit sudden increases in growth rate after several years of very slow growth. There is a well-marked daily cycle of activity, feeding being limited to the early morning and late evening. Agonistic behaviour is virtually absent. Breeding is seasonal and the males select partners from within a limited size range of tortoises. Most mating attempts are unsuccessful. On Aldabra, tortoises occur in a wide variety of habitats, in each of which they depend on a different plant species or vegetational association for food. On coastal plains the chief source of food is Sporobolus virginicus. A variety of small herbs is consumed on the barren stretches of coastal champignon. Distribution in these areas is profoundly affected by the availability of shade. Further inland, the tortoises browse heavily on Guettarda speciosa in woods dominated by this tree. They take advantage of seasonal successions in the vegetation associated with freshwater pools, feeding on each community as it develops. Most of the woody plants near the pools are ignored. On the platin, browsing is selective and the regeneration of some trees is held in check. A very important food source here is the 'tortoise turf' (a sward in which Panicum sp. is often dominant) developed under conditions of heavy grazing and susceptible to erosion by wind and the tortoises themselves. On Middle Island, where the population is small, the tortoises exert very little effect on the vegetation. Associations with other animals are mostly casual, but along the south coast dunes Coenobita rugosus is dependent on tortoise faeces for food. Fossilized tortoise bones have been discovered at many points on Aldabra, deposited in brown limestone. They probably date from before the interstadial of about 30 000 years ago. Some adult tortoises range over 7 km or more, across a variety of habitats, but many individuals appear to be sedentary. The population of South Island is enormous-of the order of 100 000 animals-with a density of about 30 hm $^{-2}$ on the platin. Higher densities are reached in Guettarda woodland. Local variation in numbers, size range and age structure depend on habitat preferences, differential movement of age classes and regional differences in growth rate. Attempts at assessing age class distribution are affected particularly by undersampling of the younger age classes, and the difficulty of counting the worn growth rings in animals with more than about 14. In the census sample, which may itself be an imperfect sample of the whole South Island population, at least 35% of the animals are below 20 years of age and only about 20% can have reached sexual maturity. More than 50 age classes may be present, but this and similar deductions are still speculative.

Morphological Aspects of Exocytosis in the Adrenal Medulla

Abstract: In the adrenal medulla of the hamster, we have clearly observed profiles which show exocytosis. Such profiles have been seen on all surfaces of the chromaffin cells, near the large extracellular spaces which are mainly occupied by the blood vessels and connective tissue and also near the narrow intercellular cleft of about 20 to 25 nm which separates neighbouring chromaffin cells. (1) Near the large extracellular spaces, the plasma membrane shows granule-containing invaginations. An electron-translucent space separates the plasma membrane and the granule which is alone in the invagination. The same diversity in size and shape may be seen among the expelled granules and the intracellular granules (see figures 1 to 7 and, plates 47 to 50). These figures look like the exocytosis aspects which have been already described in other types of cells, in particular adenohypophysis (Farquhar 1961).

The Corpora Pedunculata of Sphinx ligustri L. and Other Lepidoptera: An Anatomical Study

Abstract: The corpora pedunculata, or mushroom bodies, are paired lobes of neuropile present in the protocerebrum or dorsal brain of all insects. They are divisible into three parts: calyx, stalk and roots. The latter usually comprise two simple lobes, the a and ft lobes. The corpora pedunculata of a variety of Lepidoptera were examined. All had a double calyx-cup. Each ‘cup-cavity’ is composed of ‘globuli’ cell bodies. The broad stalk, a tract of fibres and neuropile, leads from the calyx to the complex ‘roots’—a, g and y lobes. A third group of globuli cells near the calyx gives rise to a tract leading to a second lobe-system—the tripartite Y-lobe—in the roots. As neither the Y tract nor the Y lobe has been described before in any insect, their possible homologues are unknown. The two lobe systems in the roots are closely intertwined, yet have no interaction except in the y lobe. A number of different neuron types with branches in the mushroom bodies has been described from Golgi preparations. Some (intrinsic cells) divide in the calyx and again in the roots, but do not pass out of the mushroom bodies. Others (extrinsic cells) branch in the mushroom bodies and in other areas of the brain, thus connecting two regions. Intrinsic cells arise from cell bodies in the calyx-cups or posterior to them. There are two types: one has extensive spine-covered branches in the calyx, while the second has claw-like terminals covering a narrow cylindrical field. Processes from these cells run to the a, j>and y lobes via the stalk. A wide-field accessory cell, which arises from the third group of globuli cell bodies, also has claw-like endings in the calyx. A process of this cell runs in the Y-tract to the Y-lobe. Extrinsic terminals in the calyx arise from cells branching in the antennal lobe, in an accessory optic area in the protocerebrum, in the ‘undifferentiated’ protocerebral neuropile, or in the suboesophageal lobes. The antennal terminals in the calyx are knob-like. It is proposed that they form the centre of the ‘glomeruli’ typically present in calycal neuropile. The claws of the bunched intrinsic and accessory cells probably fit around these knobs. Within the stalk, different subvarieties of intrinsic cells have been distinguished on the basis of the distribution of the side-branches and spines which they bear. The stalk is thought to be the site of extensive postsynaptic interaction between intrinsic cells. Fibres in the stalk run in bundles or groups. All the fibres in one bundle are of the same subvariety. In the roots, the subvarieties of intrinsic cells have different branching patterns. The a and B lobes are not homogeneous, but are divided into sublobes. Extrinsic fibres ramify only within one sublobe generally, though some have very large fields. The connexions of the roots are obscure. Some extrinsic fibres branch again in the ‘undifferentiated’ protocerebral neuropile; others, from the B lobe, may run to the suboesophageal lobes. There are profound differences between the internal organization of the mushroom bodies in Hymenoptera (Kenyon 1896; Goll 1967) and Lepidoptera. The functional implications of the Lepidopteran form are discussed.

Cytochemical studies of protein transport in the nervous system.

Abstract: The transport of materials within the nervous system has received much attention in recent years. Considerable information has accumulated concerning such subjects as the exchange of substances between the circulation and nervous tissue, the passage down axons of molecules and organelles originating in perikarya and the release and fate of neurotransmitters and neurosecretory agents at synapses and other neuron endings (see, for example, Wolstenholme & Porter 1968; Barondes 1969). Many investigations are underway on modulations of transport during nerve growth and regeneration and in tissue responding to injury or to other experimental alterations. However, numerous gaps remain. Of central importance to future analysis of intraneuronal transport will be the determination of details of the routes and mechanisms by which various components synthesized in the perikaryon become distributed throughout the cell. It is becoming increasingly clear that different components move along axons at quite different rates (see, for example, McEwen & Grafstein 1968). This heterogeneity may reflect the existence of a variety of intraaxonal transport pathways. Important clues derive from such work as the studies on microtubules reported by D. S. Smith in the present proceedings but much remains to be learned about possible compartmentalization of movement within axons. Similarly, the organization of perikarya must be further investigated. Neurons possess abundant rough endoplasmic reticulum, many free ribosomes, a well-developed Golgi apparatus and other features consonant with their intensive metabolic activity. Remarkably little is known, however, about most of the molecules synthesized within perikarya and about the division of labour among the organelles of the perikaryal cytoplasm.

On the Upper Triassic Mammals

Abstract: 1. The various accounts of the Triassic mammals which have been published since 1941 are summarized. 2. It is claimed that the identification of a tooth of Kuehneotherium as evidence that a similar tooth of Eozostrodon cannot be identified is fallacious. It is held that for the most part differences in the appearances of the roots of these teeth illustrate growth stages and do not provide useful taxonomic data. Eozostrodon problematicus and Morganucodon watsoni are held to be synonyms of Eozostrodon parvus . 3. The dentition of E. parvus is described and the formula is given as I f C {-PM f M f. 4. The loss of premolars, followed by the plugging of their sockets by bone, is described, and it is shown that in the lower jaw the process usually starts with the first and then the second premolars. Examples of irregular loss and plugging are given and evidence of the same happening taking place in the upper jaw is described. 5. A series of abnormal postcanine teeth are described. Some are of interest in the light they throw on possible relationships. 6. On the evidence of four cases of tooth replacement, and other relevant considerations, it is claimed that the mammalian diphyodont condition had been achieved in Eozostrodon . It is suggested that, in view of the great amount of tooth wear found in many teeth, such a reduction could only have been tolerated if the life cycle was short. This is in accordance with the very small size of the animal. 7. Some evidence on the nature of the hind limb is given. 8. Trituberculate teeth of the form Kuehneotherium praecursoris are described. It is shown that some are very similar to those of the symmetrodont Spalacotherium and support the interpretation that the form is a symmetrodont as first recognized by Kuhne and later demonstrated by Crompton & Jenkins. 9. It is claimed that the view that the eozostrodonts are triconodonts and represent the basic mammalian stock from which later triconodonts, the trituberculates, the docodonts and possibly the multituberculates evolved, is well founded.

Fine structure of noradrenaline storage vesicles in nerve terminals of the rat vas deferens.

Abstract: Most of our knowledge of storage and release mechanisms for catecholamines comes from work on the adrenal medulla (see N. & A. G. Kirshner, p. 279). There are important functional differences between the adrenal medullary cells and sympathetic neurons: in the latter the synthetic apparatus of the cell and the site of release are widely separated and re-uptake of released transmitter plays an important role in the maintenance of transmitter stores. At the ultrastructural level there is evidence for only a single population of catecholamine storage particles in each type of chromaffin cell in the adrenal medulla, whereas sympathetic neurons contain two kinds of catecholamine storage particles, whose distribution throughout the neuron is very different. It is not yet possible to explain the structural differences in terms of the functional differences. The finding that large dense-cored vesicles travel down the axon (see P. Banks & K. B. Helle, p. 305; B. G. Livett et al. , p. 359; A. Dahlstrom, p .325) suggests that they may be at least partly made in the cell body and play a role in supplying the terminal with some constituents synthesized in the cell body; whereas the finding that the small dense-cored vesicles are located almost exclusively in nerve terminals (Geffen & Ostberg 1969; Fillenz 1970) suggests that they are concerned with release, which presumably occurs mainly, if not exclusively, in this part of the neuron. In the present study Woods’s (1969) fixative has been used to re-examine the vesicles in the terminal axons of the smooth muscle coat of the normal rat vas deferens. The possible functional implications of the ultrastructural appearances are discussed.

Further Studies on the Genetics of the Mimetic Butterfly Papilio memnon L.

Abstract: Papilio memnon is a Swallowtail butterfly widely distributed in South-East Asia. The females are highly polymorphic and many of them are Batesian mimics. A previous paper gives an account of the mode of inheritance of seventeen of these female forms and here we describe the inheritance of nine from Java and Sumatra, an area we had not investigated before. We have also obtained further information on some of the forms whose modes of inheritance are not clear in the earlier paper. The nine new forms and one of those previously investigated (f. thunbergi) have been shown to be determined by the same complex locus or super-gene which controls the polymorphism already studied. The results from the present genetic investigation confirm the previous findings in P. memnon and P. dardanus that the resemblance of a form to its model is greater in the gene complex of the race in which the form is found than it is in intra-specific hybrid gene complexes. This suggests that the detailed resemblance of the mimic to its model has been built up gradually by the accumulation of modifiers. Of particular interest in this connexion is the mimic f. achates in Java and South Sumatra in which the heterozygote is a better mimic than the homozygote in the gene complex of its own race. Evidence has also been accumulated on the nature of dominance. Previously, complete dominance was present between most sympatric forms and absent between allopatric ones, both in P. dardanus and P. memnon. In contrast, the forms found in Java and Sumatra show only partial dominance between sympatric forms in most instances. However, in a hybrid gene complex the heterozygotes are even more intermediate. Thus, on these two islands the evolution of dominance has proceeded less far than elsewhere. There is ample evidence for the presence of dominance modifiers, but we are uncertain whether the absence of full dominance results from the modifiers having other, more powerful, selective forces acting upon them, or whether insufficient time has elapsed for full dominance to have evolved. In a complex Batesian mimetic polymorphism the forms must either be controlled by multiple allelomorphs at a single locus, by a group of closely linked loci (a super-gene), or by independent genes having complex epistatic interactions. In both P. dardanus and P. memnon it has been established that super-genes have been evolved. The present study throws further light on the super-gene in P. memnon. We have reason to believe that a number of very rare forms (some of which we have bred) result from crossing over rather than from point mutations, since if mutations were responsible we should have expected some of the patterns to be controlled by loci unassociated with the super-gene. This is not the case. Furthermore, in one instance, a double mutation would be required to explain the pattern. On the assumption that crossing over is the explanation of these rare forms we have postulated five loci. These control the presence or absence of tails (T), hindwing pattern (W), forewing pattern (F), colour of the basal triangle or epaulette on the forewing (E), and abdomen colour (B). Previously we had deduced that W must lie between T and B. The present study has given independent support to this order and also suggested that neither W nor B lies between E and F, and that T does not lie between W and E, the probable order being TWFEB. If the hypothesis is correct the initial mimic of P. sycorax could have been produced by a single crossover, and f. anceus, the modern mimic, evolved by subsequent minor modifications. In our investigations into the genetics of Batesian mimicry we have found that the polymorphism is controlled by a multiple allelic series at one locus or by a super-gene in P. dardanus, P. memnon and P. polytes (unpublished). This contrasts with the situation in Mullerian mimicry. In order to see whether the evolution of such super-genes is a general phenomenon or whether in other genera of Lepidoptera, and perhaps in other orders, complex epistatic interactions have been developed rather than super-genes, it will be necessary to extend this investigation outside the genus Papilio. We have already started to study Pseudacraea eurytus from Africa, which seems a particularly suitable species to use since the Batesian relationships of its forms are well documented.

Geomorphology of Aldabra Atoll

Abstract: 1. Regional setting Aldabra Atoll (latitude 9° 24' S, longitude 46° 20' E) is situated 420 km northwest of Madagascar and 640 km from the East African mainland, in the southwest Indian Ocean (figure 1). It forms one of a group of slightly elevated coral reefs to the north of Madagascar, and is thus distinguished from the sea-level coral reefs of the Farquhar group, the Amirantes, and the central Indian Ocean. The raised reefs of Aldabra, Assumption, Cosmoledo and Astove are situated on the summits of mountains approximately 4000 m high, rising from a fairly flat sea floor between 4000 and 4300 m deep. Aldabra and Assumption cap two neighbouring peaks, which are distinct at depths shallower than 2500 m, and Cosmoledo and Astove another pair, distinct above the 2000 m level (figure 2). The general bottom topography round these islands is based on surveys by H.M.S. Owen in 1962. More detailed surveys have been made of Aldabra itself, by H.M.S. Owen in 1962 and H.M.S. Vidal in 1967, and these soundings are contoured in figure 3.

Observations on Sea Turtles at Aldabra Atoll

Abstract: This paper is a preliminary report based on observations made from January to July 1968 and on expedition notes from August 1967 to November 1968. The majority of the work was carried out on adult green turtles which had been harpooned and captured by the Seychellois turtlemen at Aldabra. A small number of observations were made on nesting females and hatchlings of the same species. Males are, on average, smaller than females; this is the reverse of the expected situation and may be due to the fact that more males than females are captured. The relevance of various body proportions is discussed, as are the results of regression analysis of the measurements. Coloration of the adult carapace is extremely variable, but certain colour characteristics are strongly correlated with sex; a predictive index for sex determination is presented. Green turtles at Aldabra have similar breeding biology to other populations. Hatchling and egg measurements reflect the same trends shown by the adult females. A number of different organisms were found on adult green turtles: barnacles, leeches, isopods, green algae, and red algae. In addition, tabanids and mosquitoes were found on turtles above water. Sharks and ghost crabs are probably important predators of adults and young respectively. Only one internal parasite was found. Incidental observations were made on hawksbills. The first recorded specimen of a loggerhead from Aldabra was obtained. Information from Seychellois turtlemen relating to sea turtles at Aldabra is presented; economic importance and problems of conservation are raised.

Three-Dimensional Reconstruction of the Stacked-Disk Aggregate of Tobacco Mosaic Virus Protein from Electron Micrographs

Abstract: The three-dimensional structure of the stacked-disk rod of tobacco mosaic virus protein has been reconstructed to a resolution of about 2 nm from electron microscope images. Closed rings of seventeen protein subunits (compared with 16 $\frac{1}{3}$ in one turn of the virus helix) are stacked in polar fashion, the stacking being accompanied by an axial perturbation of periodicity 5.3 nm connecting successive pairs of rings into disks. The axial perturbation consists of a movement towards each other of the outer parts of the subunits in the two rings comprising a disk, together with a movement of the inner parts in the opposite direction. This could be explained either by a bending of parts of the subunits in the appropriate directions or by a bodily tilting of the subunits in the two rings in opposite directions.

Electrolyte transport in kidney tubule cells.

Abstract: Transtubular movement of Na and K takes place across an electrically negative cell compartment rich in K and poor in Na. Some properties of the luminal and peritubular cell boundaries with respect to ionic pump and leak characteristics are analysed. Sodium enters the tubule cell from the lumen down an electrochemical potential gradient. Peritubular Na-extrusion takes place both by an ouabain-sensitive Na-K exchange pump and by an electrogenic ouabain-insensitive Na pump. Net Na transport can be uncoupled from peritubular K uptake. It is highly likely that peritubular K uptake is pH sensitive. Once sodium has been extruded into the peritubular infoldings net Na transepithelial-transport is further critically affected by physical factors regulating capillary uptake of interstitial fluid. Several lines of evidence indicate that a large, variable intercellular transport pathway is present at the proximal tubular level. Tubular K secretion is controlled at the distal tubular level by: (1) the interplay of luminal and peritubular active K uptake into the tubule cell and (2) by a variable passive leak of K from cell into lumen across the partly depolarized luminal cell membrane. Changes in active peritubular K uptake regulate the size of a relatively small intracellular K transport pool and are critically involved in setting the rate of net tubular potassium secretion.

Chromogranin A dopamine -hydroxylase and secretion from the adrenal medulla.

Abstract: Studies of the biosynthesis, storage and secretion of catecholamines by the adrenal medulla have served as models for similar studies of the adrenergic neuron. For example, the synthesis of noradrenaline and the intracellular distribution of the biosynthetic enzymes was first described in the adrenal medulla and subsequently shown to be the same in sympathetic nerves (Blaschko 1939; Kirshner 1957, 1959; Levin, Levenberg & Kaufman i960; Potter & Axelrod 1963; Nagatsu, Levitt & Udenfriend 1964; Stjarne & Lishajko 1966; Oka et al. 1967; Musacchio 1968; Laduron & Belpaire 1968). The storage vesicles of the adrenal medulla have counterparts in the synaptic vesicles (Blaschko & Welch 1953; Hillarp, Lagerstedt & Nilson 1953; von Euler & Hillarp 1956; Schumann 1958) and the incorporation of catecholamines into the storage vesicles, and the storage complex itself, seems to be similar in both tissues, (Kirshner 1962; Carlsson, Hillarp & Waldeck 1963; von Euler & Lishajko 1963; von Euler, Lishajko & Stjarne 1963; Stjarne 1964). Recently it has been demonstrated that proteins specifically localized in the storage vesicles of the adrenal medulla are also present in the storage vesicles of sympathetic nerve endings (Hopwood 1967, 1968; Geffen, Livett & Rush 1969; Banks, Helle & Major 1969; de Potter, de Schaepdryver, Moerman & Smith 1969). There are obvious differences between the two types of vesicles (Stjarne 1964; Potter 1967), but the similarities are such as to suggest that the vesicles from both tissues serve the same physiological functions—to synthesize and store adrenaline or noradrenaline and to release these compounds in response to neural stimulation. Secretion from the adrenal medulla appears to be a good model for release of neurotransmitters at synapses in the sense that it provides and suggests experimental approaches to the problem (Geffen et al. 1969; de Potter et al. 1969). In general, the secretion of substances which are synthesized in cells and stored in subcellular organelles have many features in common (Douglas 1968; Stormorken 1969) and release of neurotransmitters at synapses may be another example of this generalized biological process. During the past few years, evidence has been presented from several laboratories that secretion from the adrenal medulla occurs by exocytosis. The simultaneous release of catecholamines, adenine nucleotides, chromogranins and soluble dopamine β-hydroxylase contained within the storage vesicles and the retention of dopamine-β- hydroxylase firmly bound to the vesicle membrane have provided critical information on this secretory process.

Some ‘partial reactions’ of the sodium pump

Abstract: The lecture describes recent work on a number of different partial reactions involving chemical transformation, and discusses the relations between these reactions and the movements of sodium and potassium ions. An account is given of recent experiments from the physiological laboratories at Yale and at Cambridge suggesting that ADP as well as ATP is required for sodium-sodium exchange, and that nucleotide is also required for potassium-potassium exchange.