Showing papers in "Biological Reviews in 1964"

The interstitial fauna of marine sand

Abstract: Summary 1. The study of the microfauna living in the interstitial water in marine or freshwater sand, the so-called interstitial or mesopsammic fauna, has made important contributions to systematic zoology during the past four decades. Most invertebrate groups are represented, and many of the morphologically aberrant forms of animals discovered in this environment belong to quite new structural types. Among the discoveries are animal groups of high systematic rank, such as the orders Actinulida (Coelenterata), Gnathostomulida (Turbellaria), Mystacocarida (Crustacea) and Acochlidiacea (Mollusca). 2. The coastal subsoil water is the environment of a special interstitial brackish-water fauna, which has been studied intensively along the beaches of Europe. This zone may be regarded as a transitional area between the submerged marine sand and the continental subterranean waters with their phreatic freshwater fauna. 3. One ecological factor of prime significance is that of space, which is dependent on the grain size distribution in a sediment, and which determines the upper size limit of organisms in a given interstitial environment. The granulometric characteristics of the sand affect the composition of the microbiocoenoses and their distribution within a beach area. 4. Wind, waves and currents cause a continuous rearrangement of the particles in the surface layer of the sand. The interstitial system of the sand is therefore most usually a very dynamic environment with special biological conditions. 5. Such physical factors as temperature and salinity vary greatly in many interstitial biotopes, particularly in the tidal zone. This implies that the interstitial organisms are physiologically adapted to endure both the seasonal variation and the often rapid changes that occur in connexion with ebb and flood. The littoral interstitial fauna is therefore eurythermal and euryhaline. 6. The vertical distribution of the interstitial fauna in a sandy beach varies with the situation in relation to low- and high-water marks. The vertical and also the horizontal distribution of the microfauna in a beach show a marked variation with the season of the year, which is usually manifested as a migration towards greater depth during the colder part of the year. 7. It is in the interstitial fauna that we find the very smallest representatives of most of the invertebrate phyla. Body sizes vary from about 0.5 to a few millimetres, and only thread-shaped organisms are longer than this. Protozoa and Metozoa in this environment have about the same dimensions. Examples of morphological regression in the interstitial fauna suggest that body lengths of about 0.5–1 mm. may be the low size limit for invertebrates. 8. Certain shapes of body dominate in the interstitial fauna. Elongated forms are favoured; vermiformity is common and may occur in groups of animals in which such a body shape is unusual (the coelenterate Halammohydra, the opisthobranch Pseudovermis and others). Another type is represented by the broad and flat forms. 9. Morphological adaptations to the biological demands of the dynamic environment are found. These consist of (a) different kinds of reinforcement of the body wall, such as cuticular scales or spines (gastrotrichs, solenogastrids) or epidermal spicules (turbellarians, opisthobranchs), which are of importance as mechanical protection; (b) an often marked ability of contraction serves a similar purpose in organisms with thin body walls (ciliates, turbellarians, gastrotrichs and others); (c) adhesive organs are found in most species, and attachment is by adhesive glands or various kinds of gripping organs; (d) static sense organs are common in different groups of animals and the importance of such organs in a dynamic environment is obvious. 10. As regards modes of nutrition, the following categories dominate: (a) predators, e.g. coelenterates, turbellarians, nematodes; (b) diatom- and epi-growth feeders, which may be divided into browsers (archiannelids, crustaceans, molluscs), pump-suckers (some turbellarians, gastrotrichs, nematodes, Psammodrilus), puncture-suckers (tardigrades) and sand-lickers (certain amphipods, cumaceans); (c) detritus-feeders (some gastrotrichs, nematodes and archiannelids); (d) suspension-feeders (sedentary forms: Monobryoxoon, a brachiopod Gwynia and the interstitial ascidians). 11. The production of gametes is usually low; 1–10 ova per female at a time is normal. Adaptations for the maintenance of the populations of low-producing species are: (a) spermatophores to ensure fertilization, e.g. Protodrilus, Microhedyle; (b) embryonic and larval development in cocoons, fixed to the substratum; (c) larval development with the suppression of a pelagic phase; (d) brood protection, e.g. Otohydra, Neril-lidae; (e) considerable extension of the period of reproduction. 12. The Ciliata are important in the sand microfauna, where they are represented by almost 90 genera. The ciliates of fine-sand habitats have been found to be the best adapted to interstitial conditions (microporal ciliates). 13. Coelenterates are represented by a rather small number of strongly aberrant forms. Among the Hydrozoa the genus Halammohydra is the best known. The genus forms a morphological series with transitions from ovoid to vermiform species, each adapted to definite interstitial environments, The peculiar bipolar genus Sphenotrochus represents the Madreporaria. 14. Of the two orders of gastrotrichs, the Macrodasyoidea, with its ca. 70 species, occurs exclusively in the interstitial fauna; the Chaetonotoidea are also common here, though this particular group has its main distribution in fresh waters. The macro-dasyoid gastrotrichs are one of the groups characteristic of the sand microfauna, and provide possibilities for us to study different kinds of adaptation to the conditions of the environment. 15. The turbellarians comprise a large and varied group found in practically all types of sand biotopes. Those best adapted to the interstitial conditions are the Kaly-ptorhynchia, and the Otoplanidae family. The order Gnathostomulida is one of the newly discovered aberrant groups. Members of this group are reminiscent of the familiar turbellarians, but differ in important structural features (cuticular pharyngeal jaws, polygonal epidermal epithelium). 16. The Nematoda in the sand fauna are rich in species and occur not infrequently in very large numbers. The distribution of the species in different sand biotopes has proved to be dependent on such ecological factors as grain size and supply of food. 17. The undoubtedly polyphyletic Archiannelida form one of the more characteristic groups of the interstitial fauna. Sixty or so interstitial species are known, but only few from other biotopes. 18. Ostracoda, Mystacocarida, Copepoda and Isopoda are the most important groups of crustaceans in marine sand. Elongated body forms or elongated shell types (Ostracoda) are common in the interstitial species. The order Mystacocarida, discovered in 1943, is known exclusively from the interstitial fauna, mainly in coastal subsoil water. These very small crustaceans, related to the copepods, have played an important role in phylogenetic discussions. 19. The best represented of the mollusc groups are the Opisthobranchia, with the order Acochlidiacea, containing ten species in the size range of 0.8–3 mm., and more or less vermiform. Other typical sand microforms are the genera Rhodope, Pseudovermis and Philinoglossa. The groups of molluscs in the sand microfauna to which least attention has been paid are the solenogastrids, which are represented in the so-called Amphioxus-sand by species about a millimetre long. 20. The remarkable Monobryozoon ambulans is the only bryozoan in this environment. It has a restricted locomotive ability and may be regarded as semi-sessile. 21. The Echinodermata are represented by a few synaptids a couple of millimetres long, e.g. Leptosynapta minuta, which by shape of body, method of locomotion, adhesive ability, static organs, etc., is very well adapted to life in the interstitial environment. 22. Recently discovered interstitial Ascidiacea are related to benthic forms in the macrofauna, where they belong to various families. Some of the interstitial species have a certain locomotive ability, due to muscle activity.

Phosphates as crystal poisons of calcification

Abstract: Summary 1. A theory has been proposed by Neuman that some metabolites which contain phosphate groups can act in the body as crystal poisons and so influence the deposition of calcium salts in skeletal structures. This theory is explained and the evidence for it reviewed. 2. A crystal poison is a compound which settles on the surface of a crystal and interferes with the continued formation of the crystal lattice. Thus crystal growth stops and the mother liquor may become supersaturated. 3. The evidence in favour of the theory is considered, both for phosphatic skeletons such as bone and calcareous skeletons such as those found in many invertebrates. 4. Many of the phosphate groups in metabolites can produce the inhibitory effect and it has been suggested that a phosphatase enzyme acts in destroying these crystal poisons by hydrolysing them at the site of mineralization. 5. Pyrophosphates are effective crystal poisons at very great dilutions, and yet they have been shown to be present in ossifying bones and in the plasma and urine of mammals. 6. Alkaline phosphatase is present during the formation of calcareous skeletons, but the explanation of the removal of a crystal poison by hydrolysis is complicated by the fact that orthophosphates also inhibit calcification. 7. These data are discussed in relation to the physiology of calcification in animals with phosphatic and with calcareous skeletons and some of the implications of the theory are evaluated.

Light relations of terrestrial plant communities and their measurement

Abstract: Summary 1. ‘Light’ covers a variety of related measures of radiant energy: the particular usage must be defined for each investigation. 2. Light in the open varies in intensity and spectral composition, both with time and over space. These variations can usually be formulated mathematically and used to predict conditions in plant communities. 3. Light may be measured directly with radiometric instruments, responding equally to all wavelengths within a certain waveband, or with photometric instruments, whose response approximates to that of the human eye. The use of the former is desirable whenever possible, as it simplifies subsequent interpretation of the results. 4. Photographs covering an entire hemisphere can be used to estimate the contribution of diffuse and direct light separately under many circumstances. They are a great help with the interpretation of many forms of measurement. 5. If the percentage of light transmitted by a plant community is to be treated as constant, diffuse and direct light must be treated separately. Even so, it is only the average transmission over considerable periods that is reasonably constant. The pattern of diffuse light distribution in the community is very different on clear and on cloudy days. 6. In general, most diffuse light penetrates the plant community near the zenith. However, on clear days the aureole of light near the sun shining through a low-altitude canopy gap may entirely alter this relationship. 7. The distribution of direct light can be analysed from tracing the path of the sun across the canopy. The sun shines unobstructed through gaps of an angular width greater than 1/2. 8. In some herbaceous communities the logarithm of relative intensity of diffuse light inside and outside the community is approximately proportional to the cumulative leaf area per unit area of ground above the level investigated. The relation varies with the angle of incidence of direct sunlight. The relation is not valid in all communities, and the errors involved in the assumption of its validity require further investigation. 9. The leafy plant community reflects and transmits light selectively. It is important to allow for the interaction of changed spectral composition on the spectral sensitivity of the instrument when making estimates of albedo or percentage light transmission. 10. Although the spectral characteristics of reflexion and transmission of individual leaves are nearly identical, this is not so for plant communities with a highly inhomo-geneous structure. 11. The percentage of total light transmitted usually increases with increasing cloud cover of the sky. The absolute intensity of diffuse light in the stand is usually higher when the sky is partly overcast than when the sky is entirely covered or clear. This is due to the increase of total light in the open with decrease of cloud cover, while the proportion of diffuse light in the total decreases with decrease in cloud cover. Provided the stand transmits more diffuse than direct light, the percentage transmission of the total will therefore fall as the total increases. 12. Daily variation of diffuse light generally follows that in the open. 13. In deciduous woods a light phase before leaf expansion and a shade phase after it can be distinguished. Each phase is characterized by a fairly constant percentage of diffuse light: that of direct light depends on daily and seasonal variation of solar altitude, increasing with increasing altitude. 14. Light measurements given as percentages of that in the open may disguise important features of the variation of absolute amounts of light. Wherever possible these absolute quantities should be calculated. Where no direct meteorological data exist, it is often possible to make reasonable assumption from other data. The precise time, place and cloud conditions should be given for each measurement, 15. Because of the great variety of instruments and techniques used, often inadequately described, comparison of results is nearly impossible. A thorough examination of the magnitude of the errors of each technique is badly needed.

The biochemistry of sodium transport.

Abstract: Summary 1. The biochemistry of ion transport has been considered in its relationship to the metabolism of phosphate compounds. 2. The supply of energy for active sodium transport has been discussed and it is concluded that the immediate source of this energy is adenosine triphosphate. 3. The stoichiometry of sodium transport in its relation to the energy source has been considered under two headings: the ratio between oxygen consumption and sodium carriage and that between use of ATP and sodium carriage. It appears that the figures for the former are uncertain enough to preclude any conclusions based upon them. Conclusions from the sodium/ATP ratio are also unlikely to be firmly based. It is thus difficult to decide whether the sodium transport system depends upon a direct conversion of ATP energy or whether it depends upon an indirect mechanism. 4. The possible mechanisms for utilization of ATP are considered from various points of view. The demonstration that enzyme systems are capable of ‘hydrolysing’ ATP in the presence of sodium and potassium is discussed. It is pointed out that such systems must conceal several steps which occur between an initial reaction and the We are indebted to Dr Alex Leaf, Massachusetts General Hospital, Dr A. E. M. McLean, Medical Research Council, London, and Dr D. Reichenberg, National Chemical Laboratory, for detailed help with the manuscript and for giving us their views on substantial parts of the work. Dr E. J. Harris, University College London, and Dr K. R. Rees, University College Hospital, Medical School, London, discussed many details with us. We are indebted to Professor E. Baldwin and Dr S. P. Datta, University College London, for making these lectures possible, and to the CIBA Foundation for assistance in making a visit to London for this purpose. The work was undertaken during the tenure of grants from the National Cancer Institute, the Burroughs-Wellcome Fund, the Damon Runyon Fund and Charles Pfizer and Co. The possibility that phosphoproteins may act as sodium carriers is discussed. The evidence is fairly strong that there is a relationship between sodium transport and these molecules, but the nature of the relationship and many important details are obscure. 5. The actions of certain drugs on sodium transport are described. Some of these, which are not usually thought of as inhibitors of active transport but rather as stabilizers, are shown to inhibit potassium uptake and sodium extrusion in nonexcitable tissues such as liver, erythrocytes and ascites tumour cells. Their effect indistinguishable from that of strophanthin-G in that it is reversed by excess potassium, both with regard to whole cells and to the sodium- and potassium-activated ATP-ases. Like strophanthin-G, these drugs inhibit phosphoprotein turnover in appropriate systems. 6. The relationship between sodium and calcium in cells is discussed. I t is pointed out that there is a reciprocal relationship between these, but that calcium transport depends upon sodium transport. Many observations which suggest that a given transport or other function depends upon the concentration of external sodium may in fact result from the influx of calcium. Similarly, the effect of strophanthin-G and of low external potassium may also be mediated by calcium influx or intracellular calcium shifts. A speculation on the nature of the permeability and other changes during the generation of the action potential is included.

The radiosensitivity of germ cells

Abstract: Summary The radiosensitivity of germ cells depends on (a) the criterion by which it is assessed, and (b) the developmental stage at the time of irradiation. For any given parameter and cell-type, the final effect exerted by ionizing radiations depends on the genetic make-up and age of the organism; type of irradiation; method of irradiation (acute, fractionated, chronic at different dose rates); oxygen tension; and temperature. Variations between different developmental stages may be due to inherent changes in oxygenation, metabolic activity, chromosomal configuration; and other factors, as yet to be determined, are probably also involved. The yield of mutations observed after irradiation of different developmental stages may be at least partly determined by the selective elimination, during subsequent development, of cells sensitive to immediate or delayed cell-death. In general, mitotically active gonia, particularly in mammals, are highly sensitive to cell-killing. In some species, inhibition of mitosis may play a considerable part in the final expression of radiation damage. Paradoxically, permanent sterilization in male rodents is most readily achieved by irradiating mitotically inactive primordial germ cells before or shortly after birth. In adult males of all species, permanent sterilization only occurs if all the primary gonia are destroyed. The last pre-meiotic generation of spermatogonia appears to be more sensitive to cell-death than are earlier generations; the difference is correlated with the relative durations of the G1, S and G2 periods, at least in adult mice. It is possible that mammalian pre-meiotic oogonia are also more sensitive than preceding generations. Interpretation of observations on insects is complicated by radiation-damage to nurse cells which may secondarily hamper the development of the germ cells. The incidence of chromosomal aberrations and mutations following gonial irradiation is relatively low, possibly due to selective elimination. A proportion of gonia which survive to give rise to differentiated gametes may carry a variety of mutations, including dominant lethals (of a special type). The claim that a reduction in dose rate lowers the yield of mutations following gonial irradiation in the male mouse has so far not been confirmed by studies on Drosophila. Primary meiocytes are relatively insensitive to cell-killing. Cells irradiated as spermatocytes may fail, or be slow to complete normal maturation division(s), or they may give rise to morphologically abnormal spermatids. The effect depends upon the phase of meiosis at irradiation. In both sexes, sensitivity to cell-death appears to decrease more or less progressively as meiotic prophase advances; in most female mammals, the trend is sharply reversed at early diplotene, when the oocytes become enveloped within primordial follicles. As the oocyte enters upon its rapid phase of growth which, in many species, is associated with vitellogenesis, sensitivity decreases again. Growing oocytes at the diplotene stage are relatively resistant to cell-killing in almost all species investigated. Due to the brief duration of subsequent stages of meiosis (diakinesis, metaphase I), sensitivity to cell-death is difficult to establish. As judged by the induction of dominant lethals, sensitivity of oocytes increases sharply between diplotene and metaphase I; in rodents, the rise becomes manifest a few hours before the onset of diakinesis. Increases of the same magnitude in the incidence of chromosomal aberrations at anaphase I and II have been scored for microsporocytes. Corresponding data for spermatocytes are less reliable, but there is some evidence indicating the same trend. In general, sensitivity to the induction of mutations is greater in meiocytes than in gonia. The yields of some mutations in the female have been shown to rise as meiotic prophase proceeds; but the relative increase as metaphase I approaches is not always as striking as that recorded for dominant lethals. Differential sensitivity to mutagenesis in spermatocytes at various stages of meiotic prophase has not been fully documented. There is some reason to believe that spermatocytes at early stages of meiotic prophase are less susceptible to mutation induction than those nearing the end of prophase. The sensitivity of secondary meiocytes has not been quantitatively assessed except by the incidence of chromosomal aberrations and dominant lethality. In both plants and animals, cells at metaphase II appear to be somewhat less sensitive than those at metaphase I. Spermatids, whose homologous stage is absent in the female, are apparently highly resistant to the induction of morphological abnormalities or cell-death, In contrast, they are highly sensitive to the induction of dominant lethals and a variety of mutations; those at early stages of spermiogenesis appear to be more susceptible than those approaching full differentiation. Corresponding changes are less readily induced in fully differentiated spermatozoa. Anoxia during irradiation diminishes the difference between spermatids and spermatozoa, without however abolishing it. Spermatozoa irradiated after insemination are more sensitive to mutagenesis than are those retained within the testes or the male genital ducts. Irradiation of differentiated gametes of either sex shortly before fertilization induces a delay in subsequent cleavage. While eggs undergo some spontaneous recovery if the period between irradiation and fertilization is prolonged, spermatozoa do not. There is at present no single working hypothesis to account for all the stage differences recorded.

The biological significance of chemical differences in bile salts

Abstract: Summary 1. The chemical nature of the bile salts is a character that must be under the control of several genes and is also affected by intestinal micro-organisms and perhaps again by the liver in the course of enterohepatic circulation. Gall-bladder bile contains the bile salts which are in use; bile from a fistula has only the primary bile salts actually produced by the liver. 2. In the only invertebrate examined, the crab Cancer pugurus, the bile-salt-like substances in the digestive juices were compounds made up of sarcosine, taurine and decanoic or 5-dodecenoic acids. 3. It has been shown for at least 13 vertebrate species (7 eutherian mammals; a bird, a boid snake, an alligator, a toad, a frog and a teleost) that the characteristic bile salts are made in viuo from cholesterol; it is assumed that this is so in all vertebrates. 4. In rats and man, 3α, 7α, 12α-trihydroxycoprostanic acid, which contains all 27 atoms of cholesterol and is made from this compound, acts as an efficient precursor of the principal bile acid, cholic acid (3α, 7α12α-trihydroxycholanic acid, C24H40O5). 3α, 7α, 12α-trihydroxycoprostanic acid conjugated with taurine is a principal bile acid in all three crocodilians examined, is also present in the bile salts of two species of Rana and has been isolated from human fistula bile. This acid is an example of substances that are intermediates in bile salt synthesis in highly evolved vertebrates and also act as bile salts in less evolved ones. 5. There is clear evidence of evolution of bile salts through the stages C27 (or C26) alcohols C27 acids C24 acids. Bile alcohols act as bile salts after conjugation with sulphate, C27 acids are conjugated with taurine and C24 acids exist in the bile as taurine and (in eutherians) also as glycine conjugates. 6. Two species of hagfish (Myxinidae) have an alcohol, myxinol, as a disulphate of unknown chemical constitution. 7. The coelacanth Latimeria chalumnae has a principal bile alcohol which is the 3β epimer of cyprinol; a little cyprinol is also present. Cyprinol, 3α, 7α, 12α,26,27-pentahydroxycholestane, is a chief bile alcohol in the dipnoan Protopterus aethiopicus and also in the five species of Cyprinidae examined. The Latimeria alcohol is (if not an artifact of the enterohepatic circulation) more ‘primitive’ chemically (i.e. nearer to cholesterol) than is cyprinol: it could give rise to cyprinol by evolution of a method for inversion at C-3. Thus, all these fishes are related by the possession of a bile alcohol type not yet found in other vertebrates. 8. About 34 teleostean fish species, excluding Ostariophysii, have cholic and in some cases also chenodeoxycholic (3α,7α-dihydroxycholanic) acids, conjugated with taurine, as their chief bile salts. In some species allocholic (3α,7α,12α-trihydroxyallo(5α)-cholanic) acid is also present: its significance is not clear. Probably most teleosts are highly evolved in their bile salt chemistry. 9. Three species of sturgeons (Acipenseridae) contain cholic and allocholic acids and small amounts of bile alcohol sulphates are also present. Identification of these may be of value in elucidating sturgeon evolutionary history. 10. Chimaera monstrosa has as its chief bile salt the sulphate of chimaerol, probably 3α,7α,12α,24ξ,26-pentahydroxycoprostane. Sharks and rays may contain a little chimaerol but the principal bile salt is the sulphate of scymnol, 3α,7α,12α,24ξ,26,27-hexahydroxycoprostane, which could arise from chimaerol by oxidation at C-27. The cholic acid found in selachians could be a dietary artifact; the bile salts of these fishes have either not evolved so far or have reached a different evolutionary result from those of teleosts. Scymnol is not an efficient precursor of cholic acid in the rat. 11. In amphibia, Rana catesbiana contains the sulphates of 5α- and 5β-ranol, i.e. 3α,7α,12α,24ξ,26-pentahydroxy-27-norcholestane-27-sulphate and its 5β epimer; in this species 3α,7α,12α-trihydroxycoprostanic acid was also found. In R. temporaria 5α-ranol sulphate is almost the only bile salt. R. nigromaculata has the trihydroxy-coprostanic acid; bile alcohols were not found. These findings put the three species in the evolutionary order R. temporaria, R. catesbiana, R. nigromaculata. Bufo vulgaris japonicus has C27 or C28 bile acids with the cholic acid nucleus and also the sulphate of 3α,7α,12α,25ξ,26-pentahydroxycoprostane. This alcohol is quite different from those found in Ranidae. Its 5α epimer has been reported in the newt Diemyctylus phyrrho-gaster and, if this is the case, it suggests a possible link between ancestors of this animal and of Bufonidae. 12. Bile alcohols have not been found in reptiles or higher vertebrates. Chelonians and platynotan lizards have (probably) 3α,7α,12α,x-tetrahydroxycoprostanic acids that may be unique to each group; 3α,7α,12α-trihydroxycoprostanic acid is a chief bile acid of crocodilians. C24 bile acids may be general in the higher lizards and in snakes. Boid snakes have pythocholic (3α, 12α, 16α-trihydroxycholanic) acid, formed by rehydr-oxylation in the liver of the deoxycholic (3α,12α-dihydroxycholanic) acid made by intestinal micro-organisms from the primary cholic acid. 3α,7α,12α,23-tetrahydr-oxycholanic acid is found in some snakes as well as allocholic acid; the latter also occurs in some lizards. 13. The few birds examined contained cholic, allocholic and chenodeoxycholic acids. In penguins the amount of cholic-allocholic acid is almost the same as that of chenodeoxycholic acid, but in a few other birds examined the latter is the principal bile acid. The germ-free domestic fowl also has allocholic acid. 14. Monotremes contain cholic, chenodeoxycholic and perhaps deoxycholic acids, as do some marsupials. Glycine conjugates have not been found in these mammals or in any lower group. Koala bile salts are almost entirely taurine-conjugated 3α-hydroxy-7-oxocholanic acid. 15. Eutherian mammals usually have cholic and chenodeoxycholic as primary bile acids. Herbivores (except bovids) often have a preponderance of dihydroxy acids, frequently as glycine conjugates; omnivores have a mixture of tri- and dihydroxy acids as glycine and taurine conjugates and carnivores have taurine-conjugated trihydroxy acids. Glycine conjugation in some species is apparently less well established than taurine conjugation; but dietary deficiencies can increase glycine conjugates. Unique bile acids, certainly or probably primary, have been found in Murinae (3α,6β,7α- and 3α,6β,7β-trihydroxycholanic acids), Sus (3α,6α,7α-trihydroxycholanic acid) and all Pinnipedia (3α,7α,23-trihydroxycholanic acid). Other substances, such as ursode-oxycholic (3α,7β-dihydroxycholanic) acid, may be wholly or partly artifacts of the enterohepatic circulation; they may nevertheless be physiologically important. Deoxycholic acid (as its glycine conjugate) is normally the chief bile acid in rabbits, although it is an artifact, but Murinae re-hydroxylate it to cholic acid. The biochemical status of 3α-hydroxy-7-oxocholanic acid is disputed. 16. Animals with primitive bile salts often also contain small amounts of more evolved types; the beginnings of bile salt evolution can be detected long before it appears likely to affect the physiological behaviour of the bile salts as a whole. 17. The physiological functions of the bile are not sufficiently understood to permit of speculation about the advantages of any particular type of bile salt. 18. Biochemical studies show that there are even more interspecific differences between bile salts than the chemistry alone suggests. Such essentially enzymic studies approach an understanding of the genes controlling the chemical characters reviewed here and may eventually throw light on fundamental questions such as the biochemical nature of vigour and senescence in evolutionary processes and the reasons why almost all classes of highly evolved vertebrates have the same C24 bile acids.

The control of plant growth and development by light

Abstract: Summary This article is devoted to photochemical reaction systems other than photosynthesis present in plants which enable normal growth and development to take place. In many higher plants (e.g. dicotyledonous seedlings) at least four different photochemical reaction systems are effective: (1) the photochemical system related to photosynthesis, (2) the photochemical system related to phototropism, (3) the phytochrome system, (4) the so-called ‘high energy reaction of photomorphogenesis’. (1) is beyond the scope of this article which is limited to those photoreactive systems in plants which directly control growth and development. The term ‘phytochrome’ is used today to signify the pigment system of photo-morphogenesis which has been most thoroughly investigated and which is apparently common to all potentially green plants. From the algae, mosses and ferns to the monocotyledons this pigment system is of fundamental importance. It is composed of a complex chromoprotein present in the cytoplasm, which can be isolated from the cell and brought into watery solution. Phytochrome has two interconvertible forms, phytochrome 660 (P 660) with an absorption maximum in the red at 660 mμ and phytochrome 730 (P 730) with an absorption maximum in the far-red at 730 mμ. The non-irradiated, dark-grown plant contains almost entirely P 660 which is stable in the dark. P 660 is converted by exposure to red light into P 730. Conversely P 730 can be reconverted into P 660 by exposure to far-red light. Even in the dark P 730 slowly changes back into P 660 Temperatures above zero and in the presence of oxygen are necessary. P 730 is the physiologically active form of the phytochrome system. Apparently it is an enzyme. As soon as P 730 is available, reactions occur which cannot proceed without it and which finally lead to the observable photo-morphogenic responses. In 1957 it was demonstrated that phytochrome cannot be the only photoreactive system in photomorphogenesis and anthocyanin synthesis, and experimental data made it necessary to suppose that a further photoreactive system plays a part. By contrast with phytochrome this other reaction system can be physiologically demonstrated only by irradiating relatively strongly for a long period of time (therefore called high energy reaction). This reaction system is not reversible. Under natural conditions of radiation it seems to be very important; it is apparently as widely distributed as phytochrome. To study the high energy reaction more closely it has been necessary to separate responses due to it from those due to phytochrome. This has been done by the use of rather complicated irradiation programmes, in situations involving either synergism between phytochrome and the high energy reaction (e.g. with mustard seedling) or antagonism (e.g. movements of the plumular hook in lettuce seedlings). The situation becomes more simple when we investigate photoresponses which are not markedly influenced by phytochrome and are largely under the control of the high energy reaction (e.g. hypocotyl lengthening in lettuce seedlings). The known action spectra of this reaction show peaks of the same order of magnitude in the blue and in the far-red range of the visible spectrum. The mode of action of the high energy reaction is far from firmly established. One hypothesis is, that the activation of an enzyme (e.g. a metal-flavoprotein) by visible radiation is the basis of the reaction. This enzyme must be of fundamental importance in metabolism because many different photoresponses are controlled through the high energy reaction. In a typical dicotyledonous seedling elongation of the hypocotyl is controlled by the phytochrome and by the high energy reaction. That is, the control of axis growth can be effectively exerted by long-wavelength visible light (above 600 mμ). A phototropic curvature, however, can be induced only by the shorter wavelengths of visible radiation, i.e. wavelengths below 500 mμ. There is thus no immediate relation between phototropism and control of stem growth by phytochrome and the high energy reaction. The germination of fern spores and the growth of the gametophytes are strongly influenced by light. In recent years it has been possible to demonstrate that several physiologically distinct photoreactive systems control development and morphogenesis during these stages: (1) the photochemical system concerned with photosynthesis, (2) the phytochrome system (germination, partly morphogenesis, partly phototropism), (3) a photoreactive system dependent on blue light mainly controlling morphogenesis and partly phototropism and germination. In the case of Dryopteris filix-mas normal morphogenesis, i.e. the rapid formation of two- or three-dimensional prothallia, can only occur under short-wave visible light (blue light). In darkness and under long-wave visible light (red light) the gametophytes grow as filaments. The control of morphogenesis by a blue-light-dependent photoreactive system is connected with the increase of protein synthesis under the influence of the light and with changes in nuclear volume and chloroplast size. These gametophytes are a clear example of the control of nuclear and cellular properties by an external factor, light. Phototropism and polarotropism of the protonernatal filaments can be induced by blue and by red light. The polarotropic response, i.e. control of the direction of growth by the plane of vibration of the electrical vector of linearly polarized light, must be regarded as a variant of phototropism mediated by an orientation of dichroic photoreceptor molecules with respect to the nearby surface. An action spectrum of polarotropism indicates that both phytochrome and the blue-light-dependent photoreactive system are involved in these movements.

Photoreceptor organelles in animals.

Abstract: Summary 1. The relatively high refractive index of rod and cone outer segments causes them to show wave-guide properties. 2. Rod outer segments have a positive intrinsic birefringence and a negative form birefringence. The former results from oriented lipid molecules, the latter from the disk structure of the outer segment. 3. Electron microscopy of outer segments shows that the disks are formed from infoldings of the surface membrane, each disk consisting of two folds adhering together on their outer surfaces. Studies of other cell membranes have suggested that their lipid molecules form a continuous or discontinuous bimolecular leaflet which is sandwiched between protein layers, and this structure probably applies to each of the disk membranes. 4. From the lipid content of rod outer segments a rough estimate of the thickness of a continuous lipid layer in each disk membrane can be made. This is only a little smaller than the requirements of a bimolecular leaflet. 5. Rhodopsin is a lipoprotein whose lipid content forms a considerable fraction of the total outer-segment lipid. This and other data suggest that rhodopsin may be a structural component of the disk membrane. 6. The initial effect of light on rhodopsin is probably to isomerize II-cis to all-trans retinene, and various thermal rearrangements follow which eventually cause the detachment of retinene from opsin. The absorption spectrum of rhodopsin is similar in situ and in solution, but the absorption spectra of the photoproducts are somewhat different. 7. Rhodopsin is strongly dichroic in the rod, indicating that the retinene molecule lies mainly in the plane of the disks. 8. Rhabdomeres, the photoreceptor organelles of many higher invertebrates, are formed from close-packed microvilli. They show a negative birefringence which probably results from the lipid molecules within the microvillar membrane. 9. All well-authenticated rhabdomere visual pigments have a retinene chromophore, and in many features the photochemical processes resemble those of vertebrate rhodopsin. The extraction processes for vertebrate and invertebrate rhodopsins are also similar. 10. The question of whether insect rhabdomeres show dichroism is still open, but there is good evidence for dichroism in some cephalopod rhabdomeres. This is probably the physiological basis for the polarized light discrimination shown by octopus. 11. Some possible mechanisms for the transmission of the light stimulus within photoreceptor organelles are discussed.

Arteriosclerosis in man, other mammals and birds.

Abstract: Summary In reviewing a problem such as atherogenesis in man and animals, it is easy to overemphasize one particular aspect of the pathogenesis and to ignore or discredit other equally well-substantiated factors. A multitude of atherogenic mechanisms have been advanced in the literature—some reasonably well proven and some quite tentative—but, rather than ignore or arbitrarily reject a number of these concepts, it will be assumed that each is a lesser or greater particle in the complex jigsaw of atherogenesis. A speculative diagram of the interrelationship of various atherogenic and anti-atherogenic mechanisms is presented in Text-fig. 4. In human atherosclerosis the initiating factor appears to be intimal thickening of the artery induced by encrustations of mural thrombus and fine films of fibrin. This mechanism has, however, only been observed on one occasion in spontaneous atherosclerosis of animals. Whether the failure to observe it in mammals and birds is due to insufficient search or whether the pathogenesis of the animal disease is different in this respect from human atherosclerosis is uncertain. It is postulated that hyperlipaemia and hypertension increase respectively the amount and rate of lipid transport across the arterial wall. From studies on the effects of feeding a cholesterol-enriched diet to the experimental animal and on the fate of subcutaneously injected cholesterol, it is concluded that accumulation of cholesterol in the tunica intima promotes proliferation of connective tissues, sclerosis and intimal thickening in the arteries in man, other mammals and birds. In man, haemorrhage into the vascularized and thickened tunica intima appears to provoke further organization and thickening. Mechanical strains on the human arterial wall are exaggerated by hypertension and, by inducing reparative changes, contribute to intimal thickening. Such strains are held to be responsible for the severity of atherosclerosis at certain sites of greatest mechanical stress, such as bends, bifurcations and orifices in arteries. Likewise, focal accentuation of experimental atheroma occurs after local application of a variety of physical and chemical insults to the arterial wall. It is suggested that intimal thickening of the human artery, caused by the three mechanisms of encrustation, lipid accumulation and mechanical stress, precipitates ischaemia of the middle zone of the tunica media. Such ischaemia would interfere with the local synthesis of lipotrophic factors required to transport lipid across the human arterial wall and would lead to further accumulation of lipid in its inner layers. A self-perpetuating circle would be set up, whereby intimal thickening encourages further mural thrombosis and lipid accumulation which, in turn, lead to further intimal thickening. In this explanation for the lipid accumulation seen in human atherosclerosis, as much emphasis has been placed on metabolic impairment of the normal outward flow of lipid through the arterial wall as on increased entry of lipid through the endo-thelium from the blood. Conversely, in experimental atheroma produced by feeding cholesterol, the accumulation of lipid in the artery appears to be a result of gross overloading of an otherwise intact system for lipid transport in the arterial wall. Hyperlipaemia has the other important atherogenic role of accelerating fibrin deposition over the arterial wall and, at the same time, inhibiting serum fibrinolytic activity. Experimental evidence suggests that hyperlipaemia with high levels of triglyceride promotes thrombosis, presumably by increasing platelet adhesiveness and the coagulability of the blood. Some hormones act against hyperlipaemia either by increasing the catabolic breakdown and excretion of lipid or by diverting metabolites away from lipid synthesis towards protein and carbohydrate metabolism. Excess lipid can also be eliminated from plasma and tissue by the action of clearing factor or lipo-lytic systems. Acid mucopolysaccharide—a component of these clearing systems—is synthesized in the atherosclerotic plaque and may, thus, contribute towards the local degradation of atheroma lipids. It can be argued, however, that it is not hyperlipaemia that is directly responsible for the deposition of lipid in human and animal arteries but, rather, an associated instability of the suspension of lipid in plasma and tissue fluid. Such instability may result from a deficiency of phospholipid and an excess of hydrophobic triglycerides, cholesterol and cholesterol esters in the β-lipoprotein molecule and other vehicles for lipid transport. Hydrophilic surface-active agents, such as phospholipid and the detergents Tritons and Tweens, appear to stabilize lipoprotein and shift the partition of lipids away from the arterial wall towards plasma. Furthermore, the arterial wall in both man and the experimental animal reacts to lipid infiltration by synthesis of phospholipid, in an apparent endeavour to stabilize infiltrated lipoprotein and to disperse precipitated lipid.

A quantitative balance between substrates and metabolic products of the mammary gland

Abstract: Summary 1. An attempt has been made to assess from published experiments, and largely for the goat, the principal compounds that are absorbed from the blood by the lactating mammary gland, the quantities of each that are absorbed during the formation of 100 ml. of milk, and the proportion of each of the major components of milk, and of the carbon dioxide expired by the gland, which is derived from each of the components of blood. 2. An assessment has first been made of which compounds of blood could, and which could not, be quantitatively significant metabolites of the gland. This has been done by calculating the maximum amount of each compound which would be available to the gland during the formation of 100 ml. of milk, from its concentration in blood together with the rate of blood flow through the gland. 3. For components of blood which could be quantitatively significant metabolites of the gland, it should be possible to discover whether or not they are absorbed in significant amounts by making arterio-venous measurements. Those measurements which have been made are considered, and rough calculations have been made of the quantity of each compound which is absorbed from the blood of the goat during the formation of 100 ml. of milk. 4. From this information, and from the results of experiments with isotopic tracers, an attempt has then been made to assess the proportion of each of the major components of milk, and of the carbon dioxide expired by the lactating gland, which is derived from each of the components of blood. 5. It is realized that the calculations made in this article are approximate. In conclusion, possible improvements in technique are briefly considered which would enable a balance of this kind to be made accurately.

Photomorphogenesis in plant stems

Abstract: Summary The large morphological differences between plants grown in the dark and those exposed to light appear to result from an effect of light on accelerating the developmental process and causing it to proceed further. Light accelerates the early phase of expansion of stems but inhibits their final growth in length. At least two photochemical processes are involved in morphogenetic responses, the red/far-red reversible reaction of the pigment phytochrome and a second process which only becomes important when irradiation is prolonged. This second process is particularly sensitive to blue light and frequently also to far-red. In many cases prolonging the exposure to red light increases the magnitude of the response, even though the phytochrome equilibrium is established within minutes of the beginning of the irradiation. Nothing is known with certainty about the pigments involved in these responses to prolonged irradiation nor what kind of relationship exists between them and the reactions mediated by phytochrome. Some evidence is presented to show that the red/far-red reaction acts earlier in the growth process than the prolonged light reaction and that, in stems, the latter acts only to inhibit elongation. There is also some indication that blue and far-red radiation do not always act identically in a prolonged light reaction. Effective auxin levels, as measured by bioassays, are lowered after transfer to red light; the depression may be only temporary, the levels rising again later. Both co-factors and inhibitors of IAA oxidase have been shown to be affected by light. Red light causes the production of an inhibitor of IAA oxidase. The effect of a natural inhibitor of IAA oxidase is prevented by blue light together with riboflavine. The co-factors and inhibitors are phenolic compounds. Anthocyanin synthesis is also dependent on light and may be related to the morpho-genetic responses. In some species both the low-energy phytochrome reaction and a prolonged light reaction, sensitive to blue and far-red, affect anthocyanin and growth. A number of flavonoid compounds and their precursors, especially the substituted cinnamic acids, affect the elongation of stems and roots, so that a change in the type and quantity of these compounds may be the cause of some of the light effects on growth; this may be particularly so in the case of the prolonged light inhibition of stem elongation. The compounds act as inhibitors and co-factors of the IAA oxidase system but they may affect growth in other ways than as regulators of in vivo auxin levels. Gibberellic acid acts by promoting stem elongation more in the light than in the dark, and it has been suggested that the light inhibition of stem elongation is caused by a lowering of the level of endogenous gibberellins. However, gibberellic acid promotes elongation whether light is promoting or inhibiting, and both the red/far-red reversible reaction and the blue light inhibition continue to be shown in the presence of saturating doses of gibberellins. Neither the prolonged light reaction nor the phytochrome reaction, therefore, appear to lower the levels of endogenous gibberellins and the light effects are probably related only distantly to gibberellin levels. In dwarf peas, however, there is some evidence that a third photoreaction acts in reducing the effectiveness of gibberellins, perhaps by causing the synthesis of a compound interfering with gibberellin activity. The low-energy red response probably concerns the activation of an enzyme by the formation of an isomer when a photon is absorbed; this activity is maintained in the dark for a while but the enzyme slowly reverts to an inactive form. The reactions catalysed by this enzyme are unknown, but it is probably a pacemaker enzyme acting at some key point in metabolism. The involvement of CoA metabolism has been suggested but there is as yet little evidence to support this. Phosphorylative capacity is enhanced by red light but there is no clear indication how directly this effect is related to the photochemical step. In the prolonged light reaction, enzyme activation or synthesis is probably involved. Protein synthesis and the formation of certain enzymes have been shown to require light. Nucleic acid metabolism has been shown to be concerned in some morphogenetic responses and in anthocyanin synthesis.

The evolution of the ovule

Abstract: Summary 1. After reviewing current theories on the origin of the pteridosperm ovule it is concluded that only one, the telomic concept, can account for all the structural variations found within the group. 2. It is therefore suggested that in at least most cases the pteridosperm ovule evolved by the enclosure of a terminal sporangium within an integument derived from a number of adjacent branches or telomes. 3. A cupule or second integument, often enclosing more than one ovule, later evolved by a similar process. 4. The available evidence suggests that both integument and cupule evolved independently a number of times and that consequently the ovule itself must have arisen several times in the pteridosperms. 5. Since the possession of an ovule is the one important feature common to the whole group, this implies that the pteridosperms must have had a polyphyletic origin. 6. It is suggested that Cordaitalean ovules are primarily radially symmetrical, having a first integument derived from several telomes, and that they became bilaterally symmetrical with the evolution of a second integument derived from only two telomes. 7. Evidence provided by the ovule supports the view that the Cordaitales are monophyletic. 8. There is no foundation for the view that the ovulate organs of the Cordaitales are stachyosporous. The same is probably true of the pteridosperms. 9. Evidence of a direct relationship between the pteridosperms and the Cordaitales is inconclusive.

Respiratory evaporation in birds.

Abstract: Summary 1. Many birds are capable of varying the rate of evaporative heat loss during respiration as a means of temperature regulation. 2. Respiratory heat loss becomes increasingly important as air temperatures rise. Above the body temperature of the bird it is the only means of heat loss. 3. The rate of respiratory heat loss varies from one species of bird to another. The rate is also dependent on environmental atmospheric humidity. 4. The rate of heat loss by respiratory evaporation is dependent on the difference in vapour pressure between that of the respiratory surface and of the inspired air, on the degree of saturation of the expired air, and on the volume of air expired per breath and per unit time. 5. There is a constant relation between breathing rate and heat production in the House Sparrow above the upper critical temperature. 6. Other things being equal, there is a constant relation between evaporative rate and the vapour pressure difference between the air and the evaporative surface, if one assumes that the vapour pressure of the respiratory surface is equal to that of water at the rectal temperature of the bird. 7. When variations due to differences in respiration rate, metabolic rate, atmospheric humidity and body size are excluded, in some species of birds the rate of evaporative heat loss is essentially constant at air temperatures above the upper critical temperature (the upper limit of the thermo-neutral zone, see p. 114, footnote). In other species the rate of respiratory evaporation increases as air temperatures rise above the upper critical temperature. 8. From this evidence and other data in the literature, there appear to be four classes of species: one in which respiratory evaporation as a temperature-regulating mechanism is unimportant or non-existent; a second in which respiratory evaporation takes place in the lungs and air sacs and in which, at air temperatures above the upper critical temperature, increased evaporation is achieved only by an increased respiratory rate; a third in which respiratory evaporation takes place in the lungs and air sacs but the evaporative rate can be enhanced without an increase in respiratory rate; and a fourth in which evaporation takes place in the more anterior regions of the respiratory tract such as the trachea or buccal cavity. 9. These four groups are interpreted as representing various stages between two extremes of specialization. One extreme is represented by species of cold arid regions in which all or most of the tidal air passes through the lung parenchyma. Respiratory evaporation and hence heat loss is thus minimized. The other extreme is represented by species of hot humid regions in which the major function of ventilation is to provide evaporative heat loss. Respiratory gas exchange is a minor purpose and only a small fraction of the tidal air traverses the lung passages.

Cephalopod phylogeny and classification

Abstract: Summary 1. A mode of origin of cephalopod buoyancy, by withdrawal of the animal from the apex of the shell followed by withdrawal of liquid from the resulting space, is suggested. 2. Buoyancy, once evolved, gave cephalopods an immediate advantage over contemporary animals and evolutionary radiation in the early Ordovician was a consequence of this. 3. The earliest cephalopods probably had curved (cyrtocone) shells. Tightly coiled shells evolved from cyrtocones in at least two separate lineages and were in the first place adapted to a benthonic existence. Straight shells (orthocones) were adapted for efficient swimming. They usually had apical counterweights to maintain a horizontal position, but in forms without counterweights, liquid-filled chambers could have served the same purpose. 4. Six evolutionary branches are described, which were distinct by the end of the Canadian (Lower Ordovician). Each branch is believed to be monophyletic, and up to a point each is characterized by certain structures or trends. 5. Increased efficiency in jet propulsion became possible in one orthocone group, consequent on loss of the ventral wall of the body-chamber, so that the mantle cavity wall could become muscular and contractile. This group gave rise to the living di-branchiates, or Coleoidea. 6. The primitive septum, which was concave forwards, remained standard in most orthocones and in some coiled shells. Folded septal edges, giving rise to more or less complex septal sutures, evolved independently in a number of coiled lineages. Their significance is unknown. 7. The siphuncle is simple and small in all coiled shells and in some orthocones. In some cyrtocones and other orthocones large siphuncles of complex structure were evolved. They usually contain deposits which are interpreted as counterweights. 8. Existing classifications of cephalopoda stem from subdivisions recognized in the nineteenth century when knowledge of fossils was inadequate. They are ill-balanced and should be abandoned. 9. A classification based on phylogeny is now possible. The six branches already described may be regarded as major subdivisions. In addition, it may be desirable to subdivide branches on the basis of important evolutionary changes. The strongest case is for the separation of Coleoidea on the grounds of the loss of the shell.

The phylum archaeocyatha

Abstract: Summary 1. The Archaeocyatha are, geologically speaking, a short-lived group, characteristic of the carbonate-shelf and reef environments of the Lower Cambrian and early Middle Cambrian. They are found in all continents, excepting South America but including Antarctica. They are the only animal phylum that has become extinct. 2. They were marine, benthonic organisms, probably with planktonic larval stages. Suggestions that larvae had skeletons and that certain small calcareous fossils were planktonic young stages of archaeocyatha are discounted. 3. They existed in depths down to 100 m., could construct bioherms at depths between 20 and 50 m. and flourished best between 20 and 30 m. Surface temperature of the water is assumed to have been that of hot regions. They are not found in sediments with a primary magnesium oxide content of more than 5–8%, and are commonest in sediments with less than 0–2–0.5 % of magnesium oxide. 4. The skeleton or cup is basically a two-walled cone with the central cavity normally empty. The overwhelming majority of cups attain a diameter of 10–20 or 25 mm. All plates are perforate except the dissepiments. The pores of the walls, but not those of the septa, taeniae and tabulae, may be complex canals or tubes bounded by variously shaped and arranged skeletal structures, and the different types of wall so distinguished are consistent within genera and species. 5. Pectinate tabulae are characteristic of the suborder Nochoroicyathina, but within a single species individuals may occur in which they are scarcely perceptible. 6. Cap-like structures at the growing end of the cone in some atabulate species raise unsolved problems on the manner of growth of the cup. 7. Archaeocyathan skeletal encrustations on normal cups are interpreted by Zhuravleva as protuberances from the intervallum of the encrusted or some other normal cup. Vologdin, however, interprets them as encrusting species and genera of archaeocyatha in which the inner wall and central cavity are not developed, and Maslov regards them as symbiotic. 8. The skeleton consists of subequigranular, microcrystalline grains of calcium carbonate about 2 μ in diameter, which Russian authors consider to have an appreciable organic content. It is considered to be external in origin by Zhuravleva and internal by Vologdin. Neither spicules nor acicular crystals have been conclusively demonstrated. 9. Ontogeny is consistent within genera and species and is of value in classification. 10. Trends of development, both in reduction and in complication, have been distinguished. 11. Skeletal carbonate sheathing walls, septa and taeniae are regarded by some, including myself, as secondary skeletal thickening, and by others as calcifications in situ of the soft parts that deposited the element sheathed. 12. Canaliculate or tubulose skeletal material found in the central cavity of some individuals is considered by Zhuravleva to be formed by protuberances from the intervallum but by Vologdin to represent calcification in situ of soft assimilative organs. 13. Vologdin, on the basis of his above-mentioned view that calcified soft parts occur, regards the soft body as cellular, with differentiated assimilative organs located in the central cavity, drawing food currents through these organs and out through the wall pores of the intervallum and depositing the skeletal elements internally. 14. Zhuravleva on the other hand, in an interpretation which I prefer, considers that assimilation and some production of sexual cells took place in the intervallum and that the central cavity was not the site of any vital activity. She thinks of the food currents as drawn into the intervallum through the outer wall pores and expelled into the central cavity through the inner wall pores. The skeleton was external, formed as in foraminifera. Digestion was analogous to that in Protozoa and took place intra-cellularly in uniform, undifferentiated cells, and not in a distinct layer of epithelial cells as in coelenterates. Thus the phylum was primarily of single-layered animals, with the possibility that some single-layered forms with undifferentiated and polar cells, and some two-layered forms might have been present in the more specialized members. She suggested that the archaeocyatha fulfil the requirements of the hypothetical blastea. 15. Following Zhuravleva's analysis, it seems probable that the Archaeocyatha are a phylum of single, multicellular organisms, with a degree of organization higher than that of the Protozoa but with less differentiation than the Porifera.

Sur la biochimie comparée des phosphagènes et leur répartition chez les animaux

Abstract: Resume 1. La repartition des phosphagenes, derives phosphoriques labiles qui servent a la reconstitution de l'acide adenosinetriphosphorique depense au cours de la contraction musculaire, a ete pendant longtemps reliee a la phylogenie. Les phosphagenes actuelle-ment connus: phosphocreatine, phosphoarginine, phosphoglycocyamine, phospho-taurocyamine, phosphohypotaurocyamine, phospholombricine, phosphoopheline, presentent, en fait, une repartition tres inegale. Les deux premiers sont les plus repandus, la phosphocreatine chez les Vertebres et plusieurs groupes d'Invertebres, la phosphoarginine chez la majorite des Invertebres. Les cinq autres phosphagenes ne se rencontrent que chez les Annelides et les Sipunculiens. 2. Si les sept phosphagenes offrent entre eux une grande parente chimique, soit parce qu'ils derivent les uns des autres, soit parce qu'ils presentent une grande similitude de structure, leur formation ne semble etre liee ni avec l'habitat ni avec la phylogenie. L'etude de leur biogenese et surtout des relations entre les differentes phosphoryltransferases constituent les nouvelles methodes d'approche des problemes poses par la diversite des phosphagenes. 3. Les Oursins camarodontes et plusieurs Annelides sont caracterises par la presence de doubles phosphagenes. L'association la plus communement rencontree est constituee par les deux phosphagenes principaux: phosphocreatine et phosphoarginine, soit entre eux, soit entre l'un de ceux-ci avec l'un ou l'autre des phosphagenes secondaires, phosphoglycocyamine, phosphotaurocyamine. La signification bio-logique des doubles phosphagenes est discuee. Summary 1. The distribution of phosphagens—labile phosphorus compounds which function in the regeneration of adenosine triphosphoric acid broken down in the course of muscular contraction—has for a long time been brought into relation with phylogeny. The seven phosphagens at present known show in point of fact an unequal distribution. Two of them are the most abundant: phosphocreatin in the vertebrates and several groups of invertebrates, phosphoarginine in the majority of the invertebrates. The five other phosphagens occur only in annelids and sipunculids. 2. While the various phosphagens are closely related chemically, either by being derived the one from the other or by having a closely similar structure, their occurrence does not seem to be related either to habitat or to phylogeny. The study of their biogenesis and especially of the relation between the different phosphoryltransferases constitute the new modes of approach to the problems presented by the diversity of the phosphagens. 3. The camarodont echinoids and several annelids are characterized by the presence of double phosphagens. The most usual association is that of the two principal phosphagens, phosphocreatin and phosphoarginin, either with one another, or one of them with one of the secondary phosphagens, phosphoglycocyamine and phospho-taurocyamine. The biological significance of the double phosphagens is discussed.