Showing papers in "Philosophical Transactions of the Royal Society B in 1952"

The Chemical Basis of Morphogenesis

Abstract: It is suggested that a system of chemical substances, called morphogens, reacting together and diffusing through a tissue, is adequate to account for the main phenomena of morphogenesis. Such a system, although it may originally be quite homogeneous, may later develop a pattern or structure due to an instability of the homogeneous equilibrium, which is triggered off by random disturbances. Such reaction-diffusion systems are considered in some detail in the case of an isolated ring of cells, a mathematically convenient, though biologically unusual system. The investigation is chiefly concerned with the onset of instability. It is found that there are six essentially different forms which this may take. In the most interesting form stationary waves appear on the ring. It is suggested that this might account, for instance, for the tentacle patterns on Hydra and for whorled leaves. A system of reactions and diffusion on a sphere is also considered. Such a system appears to account for gastrulation. Another reaction system in two dimensions gives rise to patterns reminiscent of dappling. It is also suggested that stationary waves in two dimensions could account for the phenomena of phyllotaxis. The purpose of this paper is to discuss a possible mechanism by which the genes of a zygote may determine the anatomical structure of the resulting organism. The theory does not make any new hypotheses; it merely suggests that certain well-known physical laws are sufficient to account for many of the facts. The full understanding of the paper requires a good knowledge of mathematics, some biology, and some elementary chemistry. Since readers cannot be expected to be experts in all of these subjects, a number of elementary facts are explained, which can be found in text-books, but whose omission would make the paper difficult reading.

Fat combustion and metabolic rate of flying locusts (Schistocerca gregaria Forskål)

Abstract: The nature and the amount of fuel used by flying Schistocerca gregaria Forskal have been estimated from direct analyses of the total content of fat and glycogen in control groups and in the corresponding flying groups, i.e. groups which had flown continuously for several hours. The locusts were cage-bred and resembled phase gregaria or phase transiens. Each batch was so homogeneous that it was possible to select two groups, consisting of six to fifteen individuals, which did not differ by more than 2% from one another. Because of this uniformity and because of the high rate of metabolism during flight, this rate could be estimated within about $\pm $ 15% (in one case $\pm $ 30%). For flight, the locusts were suspended at the periphery of a special roundabout (Krogh & Weis-Fogh 1952). The groups could choose the flying speed that they would naturally adopt. The speeds and durations of flight were of the same order of magnitude as observed in swarms in nature, so that some of the results could be applied to natural swarms. Analyses of the geometric similarity and of the distribution and nature of dry matter made possible an estimation of average size and gross composition of fully developed but sexually immature S. gregaria. Such standard individuals were found to contain large amounts of lipids (an average of 10% of the fresh weight), and about 85% of the stored energy was in the depot fat. The cuticle and the wing muscles of newly emerged adults (fledglings) contained only one-third of the dry matter that was found in fully developed individuals, and the accumulation of dry matter lasted 2 or 3 weeks. Fledglings were unable to fly or disinclined to fly for long. In spite of differences in age, sex, training and food, in all flight experiments fat constituted the principal source of energy, the remainder being glycogen. An average of 80 to 85% of the total energy expenditure was derived from fats or fatty acids during the first 5 h of flight. All the available glycogen was utilized during the first few hours, most of it probably within the first hour. Flight was nevertheless maintained for several hours without reduction of speed. The metabolic rate on the roundabout increased approximately with the second power of the flying speed. The speed was almost independent of temperature and varied between 2 $\cdot $ 3 and 3 $\cdot $ 7 m/s, but the speeds recorded from a large number of experiments were equally distributed around 3 m/s; the average metabolic rate of flying Schistocerca was about 75 kcal/kg/h. This corresponded to an oxygen uptake of 161. O $_{2}$ /kg/h. The values deduced for the first few minutes after the start were three times higher, and cruising rates twice as high were sometimes maintained for several hours. An average flight performance of 5 h at 3 m/s required twice as much energy as was contained in the constituent proteins of the wing muscles. Sustained flight therefore depends on large-scale transport of fuel from the stores to the muscles. The fat body delivered 85 to 90% of the energy, and the remainder was mobilized from wing muscles, legs and wings. Since even the remote cells of the wings provided stores of fuel, the mobilization was of a general nature and the transport of fuel took place via the blood. Concerning migrating swarms the following was suggested: in the morning, milling and surging of groups of locusts before mass departure tends to empty the stores of glycogen; the proper migratory flight therefore takes place at the expense of fat and, under suitable climatic conditions, the endurance of flight is proportional to the amount of fat in storage before the start. Standard individuals with 10% of fat (by fresh weight) should be able to fly continuously for about 12 h, 20 h being the upper limit (15 to 16% of fat). The amount of vegetation daily consumed by a migrating swarm probably weighs as much, and possibly three times as much, as the weight of the swarm. Sufficient time and opportunity for feeding will therefore be essential for migrations. A large migrating swarm (say 15000 tons) was estimated to require as many calories per day as do 1 $\cdot $ 5 million men. The rate at which the wing muscles of locusts converted energy was between 400 and 800 kcal/kg muscle/h; i.e. the same rates as found in hovering humming birds and flying Drosophila. Even for very intense muscular work, fat cannot therefore be regarded as inferior fuel in well-oxygenated muscles. An increasing amount of evidence from the literature favours the view that fat can be utilized directly. A possible cause for the lowered mechanical efficiency of man when fat is oxidized is the formation of ketone bodies parallel to the direct combustion of fat. On the other hand, initial mobilization seems to be slower for fat than for glycogen. When flight starts, this gives glycogen an advantage over fat, whereas the weight economy, and thus the endurance, is decisively improved by the ability to utilize stored fat; this will be further discussed elsewhere.

Mortality among voles (Microtus agrestis) at Lake Vyrnwy, Montgomeryshire in 1936–9

Abstract: Lake Vyrnwy is a reservoir surrounded by many types of habitat including newly afforested areas suitable for field voles. Other areas form ecological barriers between these populations. The purpose of the present inquiry was to discover the causes of the periodic fluctuations in numbers which occur, often simultaneously, among such vole populations. Several separate vole populations reached peak densities in 1937 and declined in 1938, in which year numbers were at a peak in most of the younger plantations. During the peak breeding season of 1937 there was an excessive juvenile mortality before August. The survival rate of the young then improved and the old animals became scarce, as they usually do at this time of year. All age groups ceased breeding in August 1937 and the survivors did not breed next spring. By contrast, populations which were at peak densities in 1938 continued breeding from May to October and the survivors bred again in 1939, though no recovery in numbers was brought about. Both in May 1937 and May 1938 high numbers were associated with unusually high body weights. A sample population was studied by marking and recapturing the animals. Most spent their lives within an area of 10 to 15 yd. diameter. Both in September 1936 and 1937 there were about 300 young voles per acre. During 1938 survival was very poor from January onwards, particularly among the males. During the time of their almost complete disappearance in 1938 or 1939 voles were not subjected to any known environmental conditions likely to have caused excessive mortality. The hypothesis is therefore advanced that death was primarily due to adverse conditions to which the parents were subjected in the previous breeding season. It is inferred ( a ) that the high juvenile mortality at that time was a symptom of severe intraspecific strife, ( b ) that intraspecific strife had deleterious effects, probably upon the hormone balance of the females, so that ( c ) their young suffered defects which reduced the longevity of those which survived the breeding season, and also ( d ) impaired their ability to produce a normal generation. Peak numbers were reached simultaneously over wider areas than seems likely by chance alone. It is argued that this must have occurred through some interaction of the independent biological units with their common weather system. Competition for space, the process believed to control excessive increase, is shown to be a possible means through which environmental changes may cause further variations in mortality rates. A sufficiently variable physical environment should thus tend to eliminate differences in density between populations and so to effect a regional synchrony of their cycles. It seems likely that periodic mortality in the North American snowshoe hare is also a delayed result of intraspecific strife. This extension of the hypothesis has implications which are at variance with some of the existing views about cycles in birds and mammals.

Water Movements in lakes during Summer Stratification; Evidence from the Distribution of Temperature in Windermere

Abstract: The first part of this paper is taken up with an historical survey of the relatively few observations, some detailed and some less so, of internal seiches (internal standing waves) in lakes. After a description of the thermo-electric thermometer employed, there follow details and illustrations of the evidence, from temperature observations, for such internal waves in the northern basin of Windermere. Two main phases could be distinguished: (i) motion under wind stress leading to quasi-steady states with some or all of the isotherms tilted; (ii) internal seiche motion which developed after the wind had dropped. These observations confirm the findings of Wedderburn and his collaborators on the Scottish Lochs (1907-15). The results from Windermere are presented, not because any such confirmation is necessary, but in order to secure belated recognition of the fact that Wedderburn’s ‘ temperature seiche ’ is not an isolated phenomenon, but is an everyday feature of movement in stratified lakes subject to wind action. As this movement is an important and largely unrecognized factor in lake environment, this paper is addressed mainly to limnologists. In its latter part, results of theoretical analyses of a detailed series of observations are presented in non-mathematical form. The applicability of a theory of oscillations in a basin with three layers of differing density (set out in an appendix by M. S. Longuet-Higgins) is tested by comparing theoretical and observed deflexions of selected isotherms from their equilibrium levels, resulting from internal waves after a gale. This theory also enables horizontal components of velocity and displacement to be calculated for each layer. Complicating factors in natural lakes are enumerated, and the influence of internal waves on lake biology and sedimentation is discussed.

Nuclear Division in Nine Species of Small Free-Living Amoebae and Its Bearing on the Classification of the Order Amoebida

Abstract: A study of nine species of small free-living amoebae has been made under standardized and reproducible cultural conditions, by a new method that enables specimens in all stages of division to be obtained easily. In all species the resting nucleus shows a Feulgen-negative nucleolus and Feulgen-positive chromatin granules. Nuclear division in these species and in other amoebae described by other workers is of two main types on which it is proposed to create two new families— Schizopyrenidae and Hartmannellidae. In Schizopyrenidae, the type genus Schizopyrenus n.g. and two other genera, Naegleria and Didascalus n.g., are defined. Naegleria gruberi, Didascalus thorntoni n.sp., Schizopyrenus russelli n.sp., S. erythaenusa n.sp. and S. atopus n.sp. are described. In Hartmannellidae the type genus Hartmannella is defined. H. glebae, H. rhysodes n.sp., H. leptocnemus n.sp and H. agricola are described. The relation of the proposed classification to previously defined families and genera of amoebae, and its bearing on phylogeny are discussed.

Jurassic Ammonites from Jebel Tuwaiq, Central Arabia

Abstract: The Jurassic system as developed along a strike of some 500 miles in the Jebel Tuwaiq, central Saudi Arabia (Nejd), is described and divided into formations, of which the names are here published for the first time, with a synopsis of their lithology and fossil contents. Apart from small collections, including only one ammonite species, made on camel journeys by H. St J. B. Philby, nothing was hitherto known of these formations; their age (except for the Middle Callovian date given by the ammonite), and the existence of most of them, were unknown until the area began to be mapped and explored geologically about 1940 by geologists of the Arabian American Oil Company, whose results are here summarized. The total thickness of marine Jurassic rocks described exceeds 1000 m., all of it in neritic facies. This sequence is divided, in ascending order, into Marrat, Dhruma, Tuwaiq Mountain, Hanifa, Jubaila and Riyadh formations, above which follows the Cretaceous system. Below the marine Marrat is the Minjur Sandstone (315 m.), of 'continental' facies, with only obscure plant remains, which possibly corresponds to the supposedly Rhaetic-Lower Lias plant-bearing Kohlan Sandstones of the Yemen. The underlying Jilh formation of Saudi Arabia contains marine Middle Triassic fossils near the top. Collections of ammonites establish the presence of marine Jurassic stages from Lower Toarcian (Lower Marrat) to Lower Kimeridgian (Jubaila); the Riyadh has not yet yielded ammonites at outcrop. The ammonites described are of extraordinary interest from the points of view of palaeogeography, correlation, phylogeny and systematics. While most of the faunas contain just enough links with other parts of the world to establish broad correlations, many are entirely new, or confined, outside Arabia, to Sinai. In the Toarcian there was faunal continuity with Madagascar and Baluchistan, in the Bajocian only with Sinai, from the Middle Bathonian onwards with western Europe. Most of the commonest cosmopolitan genera are missing from central Arabia, where there lived a succession of highly peculiar forms characterized at several successive horizons by unstable suture-lines. It has been found necessary to make eight new genera, besides three already named but hitherto not found outside Sinai, Madagascar and Baluchistan, although employing a taxonomic scale so large that some palaeontologists will consider it old-fashioned. This is believed, however, to be more useful at this stage of our knowledge than a proliferation of generic names based on inadequate material; for the area from which the collections were made is about equal to that of all the Jurassic outcrops of England. The paper concludes with a discussion of problems of evolution, speciation, correlation, and palaeogeography raised by the material. In an appendix are described relevant Bajocian ammonites from Sinai, with a hitherto unpublished section of the strata.

On the Nervous System of Saccoglossus cambrensis (Enteropneusta)

Abstract: A layer of nerve fibres is present almost everywhere at the base of the epidermis. It consists of a very thin basal layer of irregularly arranged fibres, and generally a thicker, more superficial layer of orientated fibres, which forms the main nerve cords and subsidiary systems of smaller through-conducting bundles. In the proboscis there are numerous longitudinal bundles, an anterior nerve ring round the basal periphery and a nerve loop under the pre-oral ciliary organ. The neurocord appears to be a simple conducting tract. In the collar epidermis numerous bundles are formed posteriorly, connecting with the prebranchial nerve ring. In the trunk the size of the longitudinal cords and the distribution of the general plexus is related to the degree of development of the muscles and cilia. The gut is well equipped with nerve fibres anteriorly, where it is particularly muscular. Practically all the nerve-cell nuclei lie outside the plexus of nerve fibres. They are very numerous and widely distributed. A concentration of bipolar neurones (Hess’s cells) occurs at the proboscis tip. Cells regarded as sensory on histological grounds are abundant round the base of the proboscis and in the groove of the ciliary organ. Large unipolar neurones are concentrated in the neurocord, some possessing ‘giant’ axons, which run posteriorly or anteriorly. The cilia of the epidermis are the chief agents of locomotion, those of the trunk being capable of synchronized reversal. They are aided by peristaltic contractions of the longitudinal muscles, which are controlled by the main longitudinal nerve cords. Burrowing peristalsis is controlled by the dorsal nerve cord of the proboscis. Some reactions to light, to the presence of fine particles and to adrenaline are described. The proboscis is necessary for spontaneous and varied activity, but the considerable degree of co-ordination shown is not due to any localized centre but to a longitudinal reflex path involving the main nerve cords. Rapid contractions of the anterior end are probably due to the giant axons. The peculiarities of the neurocord are difficult to interpret, except as a result of degeneration and paedomorphosis. The greater part of the richly nervous epidermis may be compared with the vertebrate neural plate.

Development and Biology of the Larva of Saccoglossus Horsti (Enteropneusta)

Abstract: Larvae of Saccoglossus horsti were reared in the laboratory, and their developmental history from the egg to the five gill-slit stage studied. The immature eggs varied from 0.23 to 0.30 mm in length and from 0.15 to 0.22 mm in breadth. They were irregular, opaque, finely granular and creamish grey in colour. They became spherical on maturing. Fertilization resulted in the rapid erection of a fertilization membrane, making the eggs buoyant. Two similar polar bodies were extruded shortly afterwards, marking the plane of the first cleavage which, with the second, was holoblastic and meridional. Subsequent cleavages were different in the animal and vegetative tiers. There was evidence of radial cleavage during the 16- to 32-cell stage. A hollow blastula was formed at the 9th to 10th cleavage stage, and gastrulation by invagination followed. The blastocoele was completely obliterated and a typical archigastrula resulted. This rapidly became uniformly ciliated and developed a telotroch around the closing blastopore. The component cilia of the telotroch imparted a slow rotatory movement to the embryo. Axial elongation and the growth of an apical tuft were accompanied by the formation of a faint annular groove. This groove marked off the definitive proboscis and the anterior part of the collar. Hatching followed 30 to 36 h after fertilization, and the larva became planktonic. During its lecithotrophic existence the larva developed a second annular groove anterior to the first, marking off the definitive proboscis from the anterior region of the collar. No definite phototaxis was detectable. Swimming movements were spasmodic. The larva rotated in a clockwise direction when viewed from the apical tuft. The spiral mode of propulsion and the propelling action of the telotroch is discussed. Settlement occurred some 2 days after hatching. A post-telotrochal adhesive patch was developed just prior to settlement, enabling the larva to adhere tenaciously to the substratum. After settlement further elongation of the main axis occurred, a well-defined proboscis, collar and trunk were rapidly differentiated. Of particular interest is the development of a long, muscular strongly ciliated post-anal tail. A dispersal period of about 6 1 2 to 7 days occurred prior to settlement. The existence of this phase prior to the animal adopting the adult mode of life demands that the mode of development of certain members of the family Harrimanidae be regarded as indirect and comparable in many respects to that known for some of the family Ptychoderidae. The mouth, anus and gill apertures became functional at much the same period, viz., at the onset of the burrowing phase. Remarkable growth movements initiated during the late planktonic phase were accelerated after settlement. This resulted in the translation of the telotroch to a latero-ventral position on the trunk and tail. The behaviour of the tail during the process of ciliary feeding, as well as during the coursing through the burrow, was observed. Ciliary reversal occurred on collar, trunk and tail. This phenomenon is discussed. Special tactile cilia have been described. They occurred on the dorsal and latero-dorsal surfaces of the trunk and tail. There was some evidence of gregariousness. The possibility of this larval habit is briefly considered in relation to the dispersal of the adults in the field. The homologies of the Enteropneusta and the Pterobranchia are discussed in some detail, with particular reference to the tail of the larval Saccoglossus horsti , and the stalk of the genus Cephalodiscus .

Late-Glacial deposits at Nazeing in the Lea Valley, North London

Abstract: At Nazeing, Essex, in the valley of the River Lea, a series of deposits has been investigated which extends back in time from the Post-Glacial climatic optimum to Late-Glacial times in the widest sense of that term. They are of special importance as bridging the time gap between the well-known ‘Arctic Plant Bed’ of the Ponder’s End stage (which occurs also at Nazeing), and the established Post-Glacial vegetational and climatic sequence. Pollen analysis of the main organic beds has permitted a general dating to be given to the various stages of formation of the deposits and this has been supplemented by a radio-carbon assay. Through the gravel sheet of the Ponder’s End stage a wide channel was cut which persisted with vicissitudes until Boreal time. At first this channel and the surrounding gravel plain were covered with organic muds and marls of a shallow lake containing stunted Mollusca of close affinity with those of Ponder’s End, and pollen indicative of rich herbaceous vegetation and an unwooded countryside. The channel was re-cut and the mere drained, and in the bed of the new channel, above an infilling of gravel, there began deposition of organic muds and then peats, a process which continued without interruption until, after a third short phase of erosion and drying in MidBoreal time (zone VI), the whole valley of the Lea was converted to fen. The later Boreal and succeeding Atlantic peats (zone VII) are sealed in by river flood clay. The Mollusca (whose determination is largely that of the late Santer Kennard) retain the general character of the Ponder’s End aggregate through the mere deposits, and the channel deposits up to the third erosion stage. The progress of drying of the mere is shown by the increasing proportion of land- to fresh-water shells. From the base of the channel which is referred to zone III, the close of the Late-Glacial period, the calcareous muds have yielded an extensive collection of plant remains, chiefly fruits and seeds belonging to ‘arctic-alpine’, ‘marsh’ and ‘ruderal’ species. Some of the species recognized have hitherto been regarded as weeds and introductions by man to the British flora; others have now a very restricted range. The pollen analyses of both the mere and channel-bottom deposits show great abundance and range of pollen of herbaceous plants, including many familiar already as Late-Glacial species and some, such as Polemonium coeruleum , newly recognized as such. It is apparent that conditions of the Late-Glacial period greatly favoured the spread of certain categories of plants, and that knowledge of this period is of the utmost importance in establishing the history of the British Flora. In the calcareous muds of the channel (zone III) and in the earlier muds beneath the lake marl the remains have been identified of four mammals of late Pleistocene character (including two species of lemming). At the close of zone III the calcareous muds yielded abundant bones of Bufo and Rana together with Lacerta vivipara . At the Early Boreal drying surface (Mx) of the channel there are also abundant land shells, and at this stage the molluscan fauna has a new and characteristic Holocene stamp, although small mammals of Late Pleistocene type survive, notably Ochotona spelaea (pika) and Microtus anglicus . A general correlation is attempted for all the phenomena described, geological, floristic and faunistic, and they are tentatively related to corresponding phenomena in Britain and north-western Europe.

A Contribution to the Study of the Eocene in Western Pakistan and Western India C. The Description of the Scaphopoda and Gastropoda from Standard Sections in the Rakhi Nala and Zinda Pir Areas of the Western Punjab and in the Kohat District

Abstract: The Scaphopoda here described comprise three new species. The Gastropoda here recorded or described comprise 138 forms, 117 of which have received specific names. Of the 23 previously named species, two had not been recorded from Pakistan or India before. Largely owing to the nature of some of the beds from which collections were made, 96 of the species described are new. Four new genera and five new subgenera are proposed, and also one new generic name to replace a pre-employed name. The fauna recorded, together with the Lamellibranchia previously described, forms part of the material constituting the basis for the consideration of the classification and correlation of the Eocene of western Pakistan and western India, which the writer has published elsewhere.

A Study of the Plasma Cell and Lymphocyte Reaction in Rabbit Tissue Homografts

Abstract: The failure of tissue grafts from one animal to another of the same species (homografts) in mammals is known to result from an active immunization of the recipient animal. But attempts to show that circulating antibody is the agent of destruction have so far been unsuccessful. The present study was undertaken chiefly to test the widely entertained alternative hypothesis that the breakdown of these homografts is, in part at least, caused by the 'lymphocytes' whose infiltration into the graft is so characteristic a feature of the process. The method was to implant a set of grafts intradermally in each rabbit from a single donor and to excise one graft for histological study every fourth day thereafter. Sections stained with methyl-green pyronin were counted for lymphocytes and plasma cells (both mature and presumptive immature). The cell counts were then subjected to various statistical tests. The invading cells were found to include, besides small lymphocytes, a large number of cells staining strongly with pyronin. Some of the latter were characteristic mature plasma cells; the rest were, according to the evidence, probably immature ones. The immature forms were largely lymphocytic in appearance, but some had reticular cell characteristics; maturation occurred at the graft site. It appeared likely that a fate of the non-pyronin-staining lymphocytes was to become plasma cells; but others underwent destruction at the time of failure of the graft's blood vessels. On the fourth day after implantation very few invading cells were present in the grafts. On the eighth day large numbers were present, and in most grafts the blood vessels were greatly dilated and engorged and tissue destruction was just beginning. At this time there was evidence of a positive relationship between the lymphocyte content of the grafts and the speed with which the grafts were going to be destroyed. No such relationship was found for the plasma cells. On the twelfth day the destruction was well advanced in most grafts and vascular breakdown widespread. No relationships were found between the concentrations of the invading cells and the stage of graft destruction achieved. But there was evidence that the increase in the number of mature plasma cells in the grafts from the eighth to the twelfth day was positively related to the amount of graft tissue destroyed during that time; the lymphocyte increment, on the other hand, tended to be negatively related to the amount of tissue destroyed. It was seen that the percentage of immature forms among the plasma cells was high in grafts at the beginning of breakdown and that it thereafter declined, but it tended to remain relatively high as long as graft tissue persisted. There was a positive relationship between this percentage in the grafts on the eighth day and the speed of graft breakdown. No graft was destroyed unless this percentage reached over fifty. It would appear to be an index of the progress of the host reaction against the graft. The grafts in one animal contained a massive infiltration of lymphocytes and plasma cells on the eighth and twelfth day without undergoing any tissue destruction. Lymphocytes were frequently observed in such close contact with the graft cells as to give the appearance of having penetrated them. Immature plasma cells were also found in such positions, but not frequently. Grafts were transplanted to animals previously sensitized by a set of grafts from the same donor. The second set of grafts in general underwent an accelerated destruction and had a much greater infiltration of plasma cells, but not of lymphocytes. Those second-set grafts which were slowest to breakdown contained most plasma cells. There was a striking correlation between the mature plasma-cell concentrations in an animal's first and second set of grafts, at any rate after graft breakdown was moderately advanced. It appeared that this cell concentration was determined by the response of the host animal rather than by the graft. Since the ranking of animals according to the speed of breakdown of their grafts was different for the first- and second-set grafts, this suggested that these cells were unlikely to be an important cause of graft destruction. In a few animals the second set of grafts was destroyed no quicker than the first set, yet their infiltration by plasma cells was much greater. This too was taken to be evidence against an important causative role for these cells. From these and other considerations it was concluded that the results do not support the hypothesis that the plasma cells which infiltrate these homografts are a significant cause of their destruction. The same would also appear to hold, though with less evidence, for the lymphocytes. At the same time it appeared likely that the plasma-cell response is specifically connected with the immune reaction. Of the main theories of plasma-cell function that of resorption would best explain the findings in these grafts. If the infiltrating plasma cells secrete specific antibody against the graft tissue this contribution to graft destruction would not appear to be significant.

The Morphology of Stauropteris burntislandica P. Bertrand and Its Megasporangium Bensonites fusiformis R. Scott

Abstract: The Lower Carboniferous Stauropteris burntislandica is described here in detail. The frond of the plant consists of a repeatedly dichotomizing branch system which is traced up to the ultimate tips. The structure of the node and degree of branching in various orders of branches is described. A reconstruction of a part of the frond is made which suggests that the frond may have been supported on an underground stem. Bensonites has now been shown to be the megasporangium of Stauropteris burntislandica which normally carries two well-developed megaspores, a condition which is unknown elsewhere in the plant kingdom. The sporangium containing small spores which was already known now becomes the microsporangium of the plant. It is suggested that heterospory may be found in other species of Stauropteris also. A comparison is then made with the Zygopterideae and the Psilophytales. Finally, the systematic position of Stauropteris is discussed in the light of new evidence.

Water Movements in lakes during Summer Stratification; Evidence from the Distribution of Temperature in Windermere: Appendix: Oscillations in a Three-Layered Stratified Basin

Abstract: Consider a rectangular basin of length l and depth h which, in equilibrium, contains three horizontal layers of fluid of different densities p 1, p 2 and p 3 and of depths h 1, h 2 and h 3. (The suffixes 1, 2 and 3 refer to the upper, middle and lower layers respectively.) Let rectangular co-ordinates ( x , y , z ) be taken with the origin in the upper surface at one end of the basin, the x -axis horizontal and the z -axis vertically downwards. The motion will be assumed to be two-dimensional and independent of the y -co-ordinate.