bluuebunny/crossref_metadata_2025 huggingface dataset:
THE GENETICAL CONCEPTION OF THE SPECIES
Authors: HARLAND SYDNEY CROSS
Published: January 2008

1. Previous work on the behaviour of genes in interspecific crosses is discussed, and it is concluded that allelomorphic relationships exist between the genes of crossable species whether these are in the same genus or in reputedly different genera

2. Genetical experiments on interspecific hybrids in six species of the genus Gossypium enable the following main conclusions to be drawn:

(a) Although allelomorphic relationships exist throughout the six species in respect of all genes examined, cases of identity (apparent or real) are practically confined to recessive genes only. Geographical isolation over a long period of time has resulted in the production of new alleles at most loci. These may be termed “species alleles”. Species endemic in the Galapagos and Hawaiian Islands are characterised by species alleles not found in mainland species.

(b) The introduction of genes from one species into another indicates that species differ not only in the mode of distribution of alleles functioning as main genes, but also in the modifier complexes accompanying such alleles. The degree to which modifier complexes differ in species is of primary importance from a taxonomic point of view.

(c) The bearing of experiments with the “Crinkled” mutant on the Fisher theory of dominance is discussed. It is shown that a number of normal alleles of crinkled exist, which are distinguishable only by their dominance potency, that the dominance relation is due to the interaction of a normal allele of specific potency with a modifier complex to which it is precisely adjusted, and that the genes constituting the dominance modifier complex have been preserved not because of their function as modifiers of initially disadvantageous heterozygotes, but because of their selective value on their own account. It is believed, however, that on the appearance of the crinkled mutant, selection probably ensued in favour of alleles with greater dominance potency, i.e. that the “Haldane effect” has been operative.

(d) Examples are given of three different ways in which homologous characters can be genetically constructed in the genus Gossypium. It is pointed out that the conception of continuous change with time in the genetical architecture of an organ is probably of profound evolutionary significance.

3. The Darwinian process of evolution by natural selection, involving mere gene substitution, has probably been the main mechanism involved in the profound changes induced in the genus Gossypium through geographical isolation.
THE SPECIFICITY AND COLLABORATION OF DIGESTIVE ENZYMES IN METAZOA
Authors: VONK H. J.
Published: January 2008

The identity of the digestive enzymes found in vertebrates and invertebrates has been discussed.

For the proteases the conclusion is reached that in the vertebrates as well as in the invertebrates (as far as investigated) the protein molecule is attacked by at least four different enzymes, a proteinase, carboxypolypeptidase, aminopolypeptidase and dipeptidase, which can be separated by adsorption. (Recent researches have, moreover, demonstrated the presence of a separate protaminase in the former trypsin of vertebrates.) The proteinase of Maia squinado has the same specificity and properties as the vertebrate trypsin. In the midgut gland of Helix a cathepsin is present. Further investigations must verify the distribution of these enzymes for other groups. In the vertebrates the action of these enzymes is preceded by that of pepsin (stomach), working in a strongly acid medium. This pepsin is nowhere found in invertebrates.

The nature and distribution of the proteases seems to be the same for all the classes of vertebrates. It is doubtful whether the enterokinases of the vertebrates are entirely identical.

The amylases of vertebrates are, as far as is known, α‐amylases. They need activation by salts (chiefly sodium chloride). The amylases of invertebrates resemble those of vertebrates. An inulase is not found in vertebrates, but is present in some invertebrates. Cellulase and hemicellulase (it is doubtful whether they are identical or not) are also lacking in the vertebrates, but are present in some invertebrates. The properties of these enzymes have been fully treated.

The disaccharases of vertebrates are saccharase, maltase and lactase. Of these, maltase is the most common in the invertebrates, occurring together with amylase (though its separation has not yet been carried out). Some invertebrates, especially Helix pomatia, are able to hydrolyse many more sugars (also tri‐ and tetrasaccharides) than the vertebrates can do. These disaccharases are still awaiting further investigation.

The fat‐ and ester‐splitting digestive enzymes of invertebrates have more the character of esterases than of lipases (or an intermediate character), whereas in the vertebrates the reverse is the case.

The differences in localization of the vertebrate and invertebrate digestive enzymes have been discussed.

It has been pointed out that in the vertebrates the digestive enzymes occur in chains and attack the food successively, whereas in invertebrates almost all the enzymes meet in the place where the digestion is performed and attack the food simultaneously. Through this localization the action of the pepsin of the vertebrates becomes possible, for which a medium with strongly acid reaction is required, and moreover the organism is protected against inundation with cleavage products.

Only in fishes (and probably amphibia) among the vertebrates is no pronounced chain of carbohydrases present, but amylase and maltase are chiefly found together in the pancreas.
SOIL CONDITIONS AND THE ROOT‐INFECTING FUNGI
Authors: GARRETT S. D.
Published: January 2008

An examination has been made of papers published during the last 15 years on soil‐borne fungus diseases of plants, with especial reference to the influence of soil conditions on infection.

In reviewing the ecology of the root‐infecting fungi, a distinction has been made, following Reinking, betweensoil inhabitantsandsoil invaders.

Thesoil inhabitantsare considered to be primitive or unspecialized parasites with a wide host range; these fungi are distributed throughout the soil, and their parasitism appears to be incidental to their saprophytic existence as members of the general soil microflora.

Thesoil invaders, to which class the majority of the root‐infecting fungi seem to belong, are more highly specialized parasites; the presence of such fungi in the soil is generally closely associated with that of their host plants. In the continued absence of a host plant, such fungi die out in the soil, owing to their inability to compete with the soil saprophytes for an existence on non‐living organic matter. This close association between thesoil invadersand their host plants thus seems to be enforced by the competition of the general soil microflora.

The influence of soil conditions upon a number of soil‐borne fungus diseases has been tabulated and discussed under the headings of soil moisture content, texture, organic matter, reaction and chemical composition. The relation of soil temperature to soil‐borne diseases has already been reviewed at length by L. R. Joneset al.(1926) and has therefore not been further considered here.
THE EXPANSION OF TAXONOMY WITH SPECIAL REFERENCE TO SPERMATOPHYTA
Authors: TURRILL W. B.
Published: January 2008

An attempt is made, within a limited space, to indicate the importance of taxonomy, especially of the Spermatophyta, to the more recently developed branches of biology, and to show that these in turn are reacting on taxonomy. Certain basic logical problems are discussed and a via media between extreme lines of development is suggested. The interactions between taxonomy and cytology, genetics, ecology, palaeontology, phylogeny, biometrics, and physiology are discussed briefly with a few selected examples. Practical suggestions for improving taxonomic methods and for increasing co‐operation between different branches of biology are made in various places throughout the text. Lastly, proposals are made that in practice should lead gradually and some way towards an “omega” or perfected taxonomy, which, idealistically, should be a completed classification of all biological knowledge.
PALAEONTOLOGICAL EVIDENCE BEARING ON HUMAN EVOLUTION
Authors: CLARK W. E. LE GROS
Published: January 2008

Palaeontological evidence bearing on the evolutionary origin of the Hominidae is provided by dryopithecine fossils of Miocene and Pliocene date. These fossils consist almost entirely of jaws and teeth. They indicate that, while the dentition of Dyropithecus was essentially simian in its general characters, in certain features, notably the cusp‐pattern and proportions of the molars, it showed some significant approach to a human type of dentition. In certain allied genera, this approach is still further emphasized by the conformation of the dental arcade. The fact that in some species of these fossil apes the characteristic specializations of modem anthropoid apes were already evident in incipient form suggests that the divergence of the evolutionary line leading to the Hominidae from that which culminated in the modem genera of anthropoid apes must probably be referred to the beginning of Miocene times.

More recent fossil apes from South Africa, even though they themselves may not bear any ancestral relation to man, emphasize the evolutionary potentialities of the Dryopithecinae for development in the direction of the Hominidae. However, a considerable gap still exists between the dryopithecine apes and the earliest known representatives of the Hominidae, a gap which can only be filled by further palaeon‐tological discoveries, with particular reference to the skull and limb characters of the former.

The accession of new palaeontological material of the Pithecanthropus group (including those fossils which have been referred to the genus Sinanthropus) has served to emphasize its hominid status. It is important to note that, despite many primitive features of the skull, brain and dentition, the limb bones of the Pithecanthropus group are closely comparable with those of modem man. It becomes clear that if the modem characters of the human limbs had already been acquired so early as the beginning of Pleistocene times, the point of divergence of the Hominidae from the Simiidae must have been correspondingly more remote.

The Pithecanthropus group almost certainly provided the basis for the develop‐nent of later types of man. Of these, one is represented by the rather specialized Neanderthal type of later Mousterian date. That this is to be regarded as an aberrant line is indicated by the fact that fossil human remains of early Mousterian and pre‐Mousterian date were less distinctively “Neanderthaloid”, and more akin in their anatomical features to Homo sapiens. There seems little doubt that these fossils represent, as a group, the direct ancestors of modem man.
THE ANTIHORMONES
Authors: COLLIP J. B. , SELYE H. , THOMSON D. L.
Published: January 2008

After a short review of the history of antihormones, the antigonadotrophic and antithyrotrophic hormones have been discussed in detail because these are the best known members of this group. The possible existence of other antihormones, especially of antigrowth hormone, antiprolactin, antiketogenic, anticortin, anti‐thyroid hormone, etc. has also been considered.

In view of the fact that many of the relevant publications have appeared in foreign languages and in journals not readily accessible to the general public, we tried to make this review as complete as possible. We felt that in the present state of our knowledge, an unbiased presentation of all the available data which may throw light on the theoretical interpretation and practical evaluation of the antihormones would prove of more value to the reader than an elaborate discussion of theories and personal views, most of which would after all have to be based on impressions rather than on knowledge.

The most important facts which, as our survey shows, are now definitely established are the following:

1. The blood of animals chronically treated with gonadotrophic or thyrotrophic preparations acquires the ability to neutralize the action of such preparations in other animals.

2. The antihormones are specific in so far as, for instance, antigonadotrophic hormone does not antagonize the action of the thyrotrophic hormone and vice versa.

3. The blood of an animal rendered immune to a certain type of a gonadotrophic preparation, though very active in neutralizing the action of this preparation, may be relatively inactive with regard to other gonadotrophic extracts. Similar examples of extract specificity have been observed concerning the antithyrotrophic hormone.

4. Neither the presence of the effector organ (the gonads in the case of the gonadotrophic and the thyroid in the case of the thyrotrophic hormone) nor that of the hypophysis is essential for antihormone formation.

5. There is little or no evidence that chemically pure hormone preparations such as the oestrogens, adrenaline, etc., may form antihormones in the true sense of the word, although the sensitivity of the organism to such preparations may decrease after prolonged treatment, In summarizing the essence of this survey, the authors emphasize, however, that the fact that pretreatment with certain hormones will cause the appearance in the blood of principles antagonistic to these hormones may be regarded as established beyond doubt. It is felt that the much‐debated question, whether these principles are hormones or antibodies, cannot be answered with certainty as yet; and even if we knew more about them the answer would largely depend on our definition of these two types of active principles.
HEARING IN INSECTS
Authors: PUMPHREY R. J.
Published: January 2008

1. The difficulties attending precise definition of auditory organs are discussed and a sketch of the early work on insect hearing is given.

2. A brief account is given of the nature of sound and of the physical conditions which different types of auditory receptor must fulfil.

3. The tympanic organs of insects, though undoubtedly of independent origin in the different groups of insects in which they occur, are shown to have a common structural plan; and the implications of this fact are discussed.

4. An account is given of the important experimental work of Regen which first conclusively established the auditory function of tympanic organs in Orthoptera, and of subsequent work upon these organs in fulfil., Lepidoptera and Hemiptera.

5. Experimental work indicating that tympanic organs may mediate a qualitative discrimination between different sounds is reviewed, and a tentative explanation of these observations is submitted.
LACTATION
Authors: FOLLEY S. J.
Published: January 2008

1. In most species oestrogens mainly stimulate mammary duct growth. In the guinea‐pig and goat they promote complete alveolar development. The mouse is the only animal in which treatment with progesterone has been found to promote mammary duct growth. In other species simultaneous treatment with oestrogens and progesterone is necessary for complete alveolar development. It is difficult to say whether or not oestrogens per se can promote alveolar development, because the adrenal cortex produces progesterone.

2. Androgens cause duct and alveolar growth in some species.

3. Some now believe that, under the influence of oestrogen, the anterior pituitary produces a “mammogenic” hormone which promotes mammary duct growth.

4. The presence of the anterior pituitary is essential for the initiation and maintenance of lactation. The anterior lobe is believed to secrete a specific lactogenic hormone (prolactin), but other anterior lobe hormones probably participate in the control of normal lactation.

5. Oestrogens may inhibit lactation during pregnancy, but it is probable that the pregnant uterus is also concerned in the inhibition.

6. The adrenal‐cortical hormone is necessary for lactation, since adrenal‐ectomized animals do not lactate, and, further, prolactin will not initiate or maintain lactation in hypophysectomized animals unless corticosterone or adrenotrophic hormone is also given.

7. The thyroid gland is essential for normal lactation: thyroxine stimulates nilk secretion in the cow.

8. Posterior pituitary extracts cause emptying of the bovine udder but do not affect the formation of milk.

9. Oestrogen treatment enriches milk in fatty and non‐fatty solids, and so does thyroxine treatment. Repeated injections of certain prolactin extracts increase the fat content of Cow's milk; certain other prolactin preparations increase the lactose content.

10. No true secretory nerves innervate the mammary gland. Lactation is disturbed in the cat if the sympathetic chains are extirpated.

11. The extraction of milk from the bovine udder depends on the reflex erection of udder tissues caused by stimulation of the teat, which also appears to cause the release of a lactogenic hormone or hormones from the hypophysis.

12. The mammary gland synthesizes lactose from blood glucose and also, probably, lactic acid. It is also possible that blood amino acids are de‐aminated by the mammary gland and used for lactose synthesis.

13. The precursor of milk fat is the neutral fat of the blood. The mammary gland probably oxidizes long‐chained fatty acids to the short‐chained acids of milk fat.

14. It is improbable that milk protein arises from blood amino acids. Plasma proteins are probably utilized for the synthesis of caseinogen, the phosphorus coming from the blood inorganic phosphate.

15. Various enzymes have been detected in active mammary tissue, which is a particularly rich source of the alkaline phosphomonoesterase. Changes in the secretory function of the mammary gland are usually accompanied by striking changes in the phosphomonoesterase content of milk.
THE DEVELOPMENT OF THE AUTONOMIC NERVOUS SYSTEM
Authors: YNTEMA CHESTER L. , HAMMOND WARNER S.
Published: January 2008

Early workers have found that the peripheral sympathetic neurons arise from mesoderm, neural crest, or neural tube. In recent years various studies on normal embryos have supported each of these contradictory views. Experimental studies have yielded results which indicate an origin from the neural crest or neural tube. We feel that a neural crest origin is most probable in the light of present information.

Experimental observations on the chromaffin cells of the suprarenal gland and the abdominal aortic bodies show that these cells have an origin in common with the sympathetic rudiments.

The ciliary ganglion, one of the parasympathetic group, can arise independently of the semilunar ganglion. Some evidence indicates an origin for the ciliary ganglion from the neural tube, although most studies on normal embryos indicate at least a partial origin from the semilunar ganglion. Understanding of the sources of the other cranial autonomic ganglia has not been advanced in recent years.

Enteric and other visceral ganglia may arise from one or more rudiments. Recent reports indicate as sources: (1) neural crest of the trunk, (2) neural crest or tube from levels of the parasympathetic nuclei in the brain stem and sacral level of the spinal cord. In addition, local differentiation from mesoderm and endoderm has been reported.

Observations upon dependent differentiation of the autonomic nerves and ganglia have been made. A formative action of preganglionic fibres upon differentiation of autonomic ganglia has been suggested. Sympathetic ganglia, however, form in the absence of these fibres. The late differentiation of the ciliary ganglion depends upon the condition of its field of distribution.

The following stages in the development of the sympathetic ganglia are suggested: (1) formation of the neural crest, (2) migration of crest cells, (3) differentiation of neuroblasts, (4) their incorporation into ganglia. It is presumed for this analysis that the neuroblasts arise from cells of the neural crest. At present methods of analysis are available which could serve to solve some of the problems indicate
AERIAL PLANKTON AND ITS CONDITIONS OF LIFE
Authors: GISLÉN TORSTEN
Published: January 2008

1. Among animals which can be transported by air currents three main types have been distinguished: (a) large forms, from a length of roughly one decimetre down to a few millimetres; (b) small forms varying between some millimetres and about 1/10 mm.; (c) animals of a microsize, smaller than 1/10; mm.

2. Large organisms are usually distributed by wind in typhoon and hurricane areas alone. During the Glacial Period, however, cyclonic disturbances proceeded along other routes, in this way creating distributional paths which are now no longer in use.

3. Small organisms have considerable possibilities of distribution by convection air currents and winds at moderate altitudes. Examples are given of such distribution over great distances. But as the animals are often strictly specialized ecologically (herbivores, parasites, etc.) they have particular difficulties to overcome in their new surroundings.

4. Numbers of micro‐organisms are constantly being driven up into the air to return again to earth in rain showers or downward air currents.

5. Micro‐organisms are very resistant to unfavourable factors met with in the air‐sea. Some may be distributed through the air in an anabiotic stage. Being often hermaphrodite or parthenogenetic, many of them can give rise to progeny from a single individual which happens to arrive in suitable surroundings. Their resistance to low temperature, low barometric pressure and drought is superior to that of all other organisms. Nevertheless, in comparison to larger forms, they are very sensitive to radiations, especially ultra‐violet, which seem to check their distribution more than that of larger forms.

6. The explanation of the fact that the microforms do not flourish everywhere is found in their very strict biotopical specialization. But wherever a biotope suitable for a certain micro‐organism exists, that organism will appear there as soon as sufficient time has elapsed to allow it to be transported through the air and to settle in the locality. The numbers which arrive are a factor in the survival and establishment of the invading species.

7. No geographical borders or barriers exist for microforms. They are often cosmopolitan, or else regionally distributed around the whole globe in certain climatic belts.

8. Under favourable conditions, especially in humid air, the harmful influence of radiation is diminished, and microforms may be transported alive by winds over greater distances than in clear and dry weather.
THE OSTEOCLAST
Authors: HANCOX N. M.
Published: January 2008

Osteoclasts, Kölliker's universal agent of bone destruction, must still be regarded as enigmatical structures. It is likely that their life span is limited to a few days. Regarded by some as resulting from fusion of relatively immobile individuals of connective tissue type, and by others of mobile cells such as macrophages, it seems a possibility that they may form from any cell, indifferently, which has assumed the ‘histiocytic state’. Osteoclasts resemble histiocytes in their reaction to supravital neutral red, in their brisk motility and in the differentiation of a superficial ecto‐plasmic layer into an ‘undulating membrane’ in tissue culture. There is no direct evidence that osteoclasts erode bone, but their constant occurrence in zones where absorption is taking place, together with the associated histological picture and especially their striated border, suggest that their presence is more than incidental. A linear orientation of cytoplasmic ultramicrons may be reflected in the striated border, which may thus constitute a cytoplasmic zone adapted for the transfer of material into or out from the cell. There is practically no evidence upon which to base an explanation of how osteoclasts could erode bone. The cells form in response to such a wide variety of normal and experimental stimuli that at least in part a local action on the bone seems likely. Local humoral factors, emanating from the bone, may be responsible for the determination of osteoclasts, and the formation of giant cells under the influence of injected phthioic acid seems to provide a valid analogy. It may be that the factors reside in the ground substance. The process of osteoclastic absorption does not appear to be regulated by the nervous system. Further experiments should be undertaken to test the ability of osteoclasts to erode bone and to ascertain whether bone about to be absorbed differs constitutionally from normal bone.
MUSCLE ACTIVITY and MUSCLE PROTEINS
Authors: DUBUISSON M.
Published: January 2008

1. If it were experimentally possible to examine muscle extracts made during defined phases of the contraction cycle, the relation of muscular work to changes in the composition of such extracts might then be elucidated. The changes of normal muscle proteins in relation to muscular function, could then be considered from a truly physiological point of view.

2. Such a study is possible: the technique for making extracts (a) from resting and relaxed muscle, (6) from fatigued muscle, and (c) from contracted muscle, are described. Reasons are given for preferring certain extracting agents. Advantages of the electrophoretic method of analysis are discussed.

3. Proteins extractable at μ≪ 0–15 can be assumed to be in solution in the muscle cell. Fatigue and contraction do not modify their qualitative or quantitative distribution in the extracts.

4. Proteins appearing in an extract of an ionic strength > 0–15 ≪ 0.5 must be assumed to be fixed in the cell as insoluble complexes; they can be released by strong salt solutions, which break down certain linkages. To this group belong actomyosin, β1 bT2 and γ myosins obtained from normal resting muscle.

5. The qualitative and quantitative composition of extracts at μ 0–35‐0‐50 depends on the functional state of the muscle, which influences the protein linkages. Thus, during all kinds of contraction (maximal contraction) or contracture (contracture by monoiodoacetate, strychnine or rigor mortis), β1 and β2 myosins become inextractible, while a new protein, contractin, appears.

6. These results are discussed. It appears that the contractile mechanism is characterized by the formation and dissociation of protein complexes whose constituents are numerous and mostly unidentified, practically nothing is known as to the nature of their linkage forces.

7. This review deals with an early stage in the physiological study of muscle proteins: the problem is to determine which of the proteins really belong to the structures which take part in muscular contraction and relaxation–by the use of methods which test the strength of the bonds holding these proteins in position. The use of extracting agents of various ionic composition, which may act selectively on these bonds, may be expected in the future to yield important additional information.
THE SPIRAL STRUCTURE OF CHROMOSOMES
Authors: MANTON I.
Published: January 2008

. i. Sufficient examples of spiral structure of chromosomes are now known from dicotyledons, monocotyledons, pteridophytes and perhaps gymnosperms, together with some animals, to show that the phenomenon is a fundamental one in the plant and animal kingdoms, at least in the higher groups.

2. Various methods found to be effective for revealing the spiral are listed, though the spiral itself cannot be an artifact.

3. Since 1939, new observations have been made on the following principal topics: (a) chromonema length; (b) direction of coiling, especially in a somatic chromosome; (c) prophase development leading to generalizations about ‘gyre elimination’ as a normal part of the spiralization cycle; (d) geometrical form of the spiral.

4. Unification of terminology is recommended by general adoption of the terms plectonemic and par anemic to describe the geometrical form of the spiral. The term ‘standard coil’ is recommended to replace ‘minor spiral’ for contrasting the major spiral with those of other types of division.

5. The need is stressed for further evidence on the minor spiral in the strict sense.

6. The importance of the interpretation of the ‘telophase split’ and of the origin of relational coiling for an understanding of the functional importance of the whole phenomenon of spiral structure is stressed. The suggestion made in earlier publications is repeated that the functional significance of the spiral might be that of co‐ordinating the component strands of a chromosome so that these may act in a unified manner when outside the resting nucleus.
MALFORMATIONS EMBRYONNAIRES D'ORIGINE CARENTIELLE
Authors: GIROUD Par ANTOINE
Published: January 2008

The early development of an organism is a critical stage which many factors may influence unfavourably. Maternal nutritional deficiencies, especially vitamin deficiencies, can disturb the development and bring about the most diverse malformations, affecting the nervous system, eye, vascular system, kidneys, limbs, etc. The teratological effects of deficiencies in vitamin A, vitamin B2, pantothenic acid and folic acid are firmly established.

Deficiencies not only produce malformations in the embryo. They may merely retard development, but they can also cause various lesions, and among others lesions which are analogous to those brought about in the adult by nutritional deficiencies.

The gravity of the result of deficiencies varies greatly. It may be negligible or it may end in the death of the embryo or sterility of the mother. The effect is a function of the intensity of the deficiency, as shown by chemical estimations of the vitamin in question.

A slight deficiency may produce a malformation. It may therefore occur readily, the more so as it may result from various causes, such as an insufficient exogenous or endogenous supply, a disequilibrium of the ration, imperfect utilization, etc.

Deficiencies act on the embryo as on the adult, by a disturbance of metabolism, for it is known that many vitamins are essential constituents of enzymatic systems. The results of the deficiencies depend upon the tissues or cells with which these systems are specially concerned. At an early stage such metabolic disturbances may affect organizers and so cause anomalies in development, that is, deformities.

Here, as elsewhere, genetical factors may intervene in restraining or facilitating the effect of a deficiency.

It is probable that these phenomena, observed in several types of birds and mammals, are of general occurrence, to be found also in man and in domestic animals.

From the practical point of view it follows that maternal nutrition should be closely supervised.
BIOLOGICAL ASPECTS OF SENESCENCE
Authors: COMFORT ALEX
Published: January 2008

1. Senescence is treated as a generic term for the processes in certain organisms which lead to a decreasing power of homoeostasis with increasing age.

2. The presence of these processes in a species can be inferred from life‐tables prepared and interpreted with suitable precautions. It cannot be inferred from the desultory examination of anatomical changes in species of unknown life cycle. Secondary criteria of senescence, e.g. decline of reproductive capacity are of value in judging the degree of age change in individuals of well‐studied species.

3. Decreasing homoeostasis with increasing age is known to arise from different causes in different phyla. No single general or ‘inherent’ process can be invoked to explain all types of senescence.

4. Senescence occurs only rarely in the wild state, and except in large or social animals regularly occurring senescence is a feature of domestication.

5. Susceptibility to senescence is apparently not universal in Metazoa, and may not be so in vertebrates. Probable exceptions to its occurrence are among forms where somatic cells are continually replaced, where there is no limiting size, or where virtual attainment of a limiting size is accompanied by a persisting capacity for growth.

6. The ‘senescence’ of asexually reproducing protozoan stocks is not a phenomenon directly analogous to metazoan senescence.

7. The specific age of invertebrates and of mammals can be modified by factors modifying the rate of development. The evidence in mammals indicates that senescence results from the attainment of a developmental stage, or from the exhaustion of developmental ‘programme’ not from the cessation of growth per se.

8. The specific age varies widely between inbred stocks. Longevity is most readily produced by heterosis, and is probably a correlate of heterozygosity.

9. The role of postponed lethal genetic effects, and of the reduction of the selection value of the individual with increasing age, in the evolution of senescence is discussed.

The materials for this article were collected during the tenure of a personal grant from the Nuffield Foundation for study and research on the biology of senescence. I am also very grateful to many colleagues who have furnished me with facts and criticisms, without bearing any responsibility for the uses to which I have put them, and to Miss Rosemary Birbeck, for her work in preparing the manuscript.
THE TRANSPORT OF CALCIUM and OTHER CATIONS IN SUBMERGED AQUATIC PLANTS
Authors: LOWENHAUPT BENJAMIN
Published: January 2008

Photosynthetic bicarbonate assimilation and cation transport by aquatic plants are reviewed. It is suggested that these two processes stand in a causal relation to one another. A number of observations of cation transport not directly associated with photosynthesis are also reviewed, and are related to current concepts of active transport in the plant kingdom.

These characteristics of cation transport have been observed in many submerged aquatic plants:

Cations are transported through the leaves in the light but not in the dark.

Cations are accumulated at the abaxial leaf surface from the contiguous external medium and are excreted from the adaxial surface into the medium. Therefore accumulation and excretion can be studied separately.

A new theory of cation transport in bicarbonate‐assimilating aquatic plants is presented. The theory entails the following propositions:

Two active membranes pump cations through the leaf in the light. The membrane on the abaxial leaf surface pumps cations into the leaf; that on the adaxial surface pumps cations out of the leaf.

The cell plasma membranes on the abaxial and adaxial leaf surfaces form these two active membranes.

In the light–i.e. when the transport mechanism is functioning–the biochemical reactions of transport reach steady‐state levels. These levels are determined by the rates of reaction between the constituents. One can therefore alter the steady‐state levels by suitably altering the conditions of one or more of these reactions.

In the dark–i.e. when the transport mechanism is not functioning–the biochemical constituents reach equilibrium levels. The equilibria can be altered by changing the environment of the leaf.

The reactions of transport supply links of a respiratory chain.

The reactions of transport synthesize a bicarbonate‐accepting compound at the plasma membrane.

Evidence for each of these propositions is discussed.

The theory is considered applicable, with appropriate modification, to cation transport in a variety of cells.
PHOTORECEPTOR ORGANELLES IN ANIMALS
Authors: MOODY M. F.
Published: January 2008

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.
SUR LA BIOCHIMIE COMPARÉE DES PHOSPHAGÈNES ET LEUR RÉPARTITION CHEZ LES ANIMAUX
Authors: THOAI NGUYEN VAN , ROCHE JEAN
Published: January 2008

1. La répartition des phosphagènes, dérivés phosphoriques labiles qui servent à la reconstitution de l'acide adénosinetriphosphorique dépensé au cours de la contraction musculaire, a été pendant longtemps reliée á la phylogénie. Les phosphagènes actuelle‐ment connus: phosphocréatine, phosphoarginine, phosphoglycocyamine, phospho‐taurocyamine, phosphohypotaurocyamine, phospholombricine, phosphoophéline, présentent, en fait, une répartition très inégale. Les deux premiers sont les plus répandus, la phosphocréatine chez les Vertébrés et plusieurs groupes d'Invertébrés, la phosphoarginine chez la majorité des Invertébrés. Les cinq autres phosphagènes ne se rencontrent que chez les Annélides et les Sipunculiens.

2. Si les sept phosphagènes offrent entre eux une grande parenté chimique, soit parce qu'ils dérivent les uns des autres, soit parce qu'ils présentent une grande similitude de structure, leur formation ne semble être liée ni avec l'habitat ni avec la phylogénie. L'étude de leur biogenèse et surtout des relations entre les différentes phosphoryltransférases constituent les nouvelles méthodes d'approche des problèmes posés par la diversité des phosphagènes.

3. Les Oursins camarodontes et plusieurs Annélides sont caractérisés par la présence de doubles phosphagènes. L'association la plus communément rencontrée est constituée par les deux phosphagènes principaux: phosphocréatine et phosphoarginine, soit entre eux, soit entre l'un de ceux‐ci avec l'un ou l'autre des phosphagènes secondaires, phosphoglycocyamine, phosphotaurocyamine. La signification bio‐logique des doubles phosphagènes est discuée.

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.
THE ENZYMIC BASIS OF SPECIFIC ANTIBACTERIAL ACTION BY STRUCTURAL ANALOGUES
Authors: RICHMOND M. H.
Published: January 2008

1. The mechanism of action of structural analogues is examined to discover the extent to which their properties make them effective antibacterial agents in vivo.

2. Two main types of structural analogue may be recognized. First, there is the type which competes with a natural metabolite for a recognition site on the surface of a protein. Secondly, there are a few examples–notably cycloserine, and possibly penicillin–which inhibit non‐competitively by reacting covalently with an enzyme to inhibit its action. In general, inhibitors which react covalently are more effective in vivo than those which inhibit competitively.

3. Analogues which inhibit competitively act in three main ways: they may compete at the active centre of a single enzyme, or exert a ‘false feedback’ inhibition of the endogenous supply of an essential metabolite, or repress the formation of enzymes necessary for the biosynthesis of an essential metabolite.

4. Although structural analogues which inhibit competitively in one of these three ways can cause temporary inhibition in the growth of bacterial cells, their bacteriocidal effect is low, since resistant bacterial populations readily emerge.

5. Resistance to structural analogues which inhibit competitively at the active centre of a single enzyme may occur physiologically by the accumulation of the precursor to the inhibited enzyme.

6. Resistance to structural analogues which inhibit competitively may also occur by mutation. In the case of analogues acting at the active centres of enzymes, mutation may lead to resistance by lowering the affinity of the relevant enzyme for the analogue. Resistance to structural analogues acting as ‘false feedback’ inhibitors occurs when a mutation causes the synthesis of an enzyme with a lowered affinity for the structural analogue as a feedback inhibitor. Similarly, organisms resistant to the action of analogues as repressors are probably the result of a mutation which lowers the affinity of the ‘genetic repressor’ for the analogue in its role as the ‘low molecular weight repressor’.

7. Inhibitors which react covalently with an enzyme have certain advantages not found with analogues which act competitively, and these are discussed in relation to the mode of action of the cholinesterase inhibitor, di‐iso‐propylfluorophosphate. One advantage of this type of inhibitor is that reversal by the normal enzyme substrate does not readily occur. Secondly, this type of inhibitor is active at appreciably lower concentrations than simple competitive inhibitors.

8. The antibacterial action of cycloserine and penicillin are examined to see to what extent they are examples of structural analogues which react covalently with essential enzymes.

9. The fact that analogues which react covalently with enzymes are more effective inhibitors than analogues which act competitively, suggests that some form of covalent reaction may often be involved in the action of antibiotic substances.
CHEMICAL EMBRYOLOGY OF THE CRUSTACEA
Authors: GREEN J.
Published: January 2008

1. The dry weight of a neonate crustacean is sometimes lower than the initial dry weight of the egg, owing to utilization of respiratory substrates, as in Daphnia, where the dry weight decreases by 16–25 %. In Artemia any loss is compensated by an uptake of salts so that there is no change in dry weight during the course of embryonic development. The embryos of Ligia receive nutrients secreted into the maternal brood pouch, and the dry weight of the neonate is greater than the initial dry weight of the egg.

2. Early embryos of Simocephalus, Artemia and Balanus consume less oxygen per unit dry weight than older embryos. The increase in oxygen consumption from early to late embryos is approximately six to eightfold.

3. Oxygen consumption decreases when the rate of embryonic development of Artemia is reduced by increasing osmotic pressures in the external medium.

4. Glycogen is formed rather than utilized in the embryos of Simocephalus and Artemia. In the latter the main carbohydrate reserve is trehalose, which is transformed to glycogen and glycerol. The relative formation of these two substances is influenced by external osmotic pressures. At high external osmotic pressures more glycerol is formed, and this aids osmotic rupture of the tough outer shell of the egg.

5. Trehalose seems to be important in relation to the dormant state of Artemia embryos. The embryos which develop rapidly in the maternal brood pouch contain much less trehalose than those which become encysted and dormant.

6. The proportion of the initial lipid content of a crustacean egg that is utilized during development is very variable. In Homarus 60% disappears by time the neonate emerges, in Ligia 32%, and in Artemia the decrease is very slight, or there may even be a slight increase.

7. Haemoglobin in the eggs of Cladocera does not appear to act as a respiratory pigment, but does serve to accelerate development in poorly aerated water. It is suggested that the main function is to act as a supply of stable protein.

8. The haemochromogen found in the gut of late embryos of Daphnia appears to be formed in part at least from haemoglobin, which diminishes in concentration as development proceeds.

9. Breakdown of haemoglobin during embryonic development of Daphnia is not accompanied by formation of bile pigments.

10. Biliverdin is synthesized in the embryonic eyes of Polyphemus but not elsewhere in the embryo.

11. The carotenoproteins in the eggs of many different crustaceans break down towards the end of embryonic development, liberating free carotenoid. It is suggested that these proteins are stabilized and held in reserve by linkage to a carotenoid until a particular stage of embryonic development has been reached.

12. Metabolic pathways in the formation of astaxanthin from β‐carotene may involve monoketo and diketo carotenes, or by an alternative route monohydroxy and dihydroxy carotenes.