bluuebunny/crossref_metadata_2025 huggingface dataset:
INTERRELATIONSHIPS AND TAXONOMY OF THE DIGENETIC TREMATODES
Authors: STUNKARD HORACE W.
Published: January 2008

The purpose and objective of classification is to portray genetic relations by taxonomic symbols. Adoption by trematodes of a parasitic mode of life has induced changes in nutrition, physiology, morphology, life cycles and development. These adaptive modifications have resulted in both convergent and divergent evolution. Criteria for determining genetic relations must be assessed with caution and no single measure can be accepted as reliable or adequate. Although certain features appear to be correlated, they may have developed independently and the evaluation and interpretation of diagnostic characters is very difficult. Types of adhesive organs and the extent of their development may be associated with the site of infection, but life histories and the type of development afford more significant information concerning genetic relations. Consideration of morphological and developmental data lead to the conviction that in the Digenea, the higher taxonomic units have little phylo‐genetic or systematic significance. It is proposed therefore, to suppress the orders Gasterostomata and Proso‐stomata, and in the latter the suborders, Amphistomata, Distomata, Monostomata, Strigeata, Bucephalata, Schisto‐somata and Clinostomata. Although superfamily groups may be recognized, their limits and interrelations are not yet clearly defined and their erection should await more complete information. Former systems for classification of adults were based on morphological features, some of which have proved unreliable, and life‐history data are yet too meagre for final evaluation and application. Classifications of larval stages, based on types of asexual generations or on larval structures such as form of tails, presence of stylets, etc., have proved more unsound than classifications of adults. Only an analysis, evaluation and correlation of all data can produce a truly natural system. Such a system must be based on and portray the evolutionary history of the trematodes. Phylogenetic considerations are reviewed and applied to taxonomic problems.
LIVER MORPHOLOGY
Authors: ELIAS HANS
Published: January 2008

The liver is constructed according to one fundamental plan in all vertebrates. It is a continuous mass of cells tunnelled by a labyrinth of lacunae, in which the network of sinusoids is suspended. This structure is termed a muralium (‘wallwork’, system of walls). The walls are predominantly two cells thick in lower vertebrates and in some primitive birds. They are only one cell thick in a few other primitive birds and in all song birds and mammals.

Where the liver parenchyma touches the portal and hepatic canals, and the external capsule, it is bounded by the limiting plate, a continuous sheet of liver cells.

The portal veins send short inlet venules through holes in the limiting plate to supply the sinusoids. Individual sinusoids empty into the central veins.

The sinusoids are lined by one kind of cells: potential phagocytes. These cells never bridge the lumen of sinusoids.

The hepatic arteries have direct inlets into the paraportal, intermediate and centrolobular sinusoids.

Meshes of bile canaliculi surround each individual liver cell in mammals. In lower vertebrates they rarely form meshes. They drain into intralobular and periportal ductules.

The liver lobules are ephemeral. They are only expressions of the temporary blood‐pressure conditions. Reduction of the portohepatic blood‐pressure gradient abolishes hepatic lobules and creates ‘portal’ lobules. This process is reversible.

In man, each portal triad (portal vein branch, hepatic artery branch, hepatic duct tributary) has its own sharply delimited territory. There are normally no anastomoses between territories.

These portal segments are united by the hepatic veins which cross the boundaries of portal segments.

The major branches and roots of these vessels and ducts have been mapped and named. Applications to surgery are suggested.

The uniform structure of adult livers arises from a great diversity of developmental processes. Twelve fundamentally different modes of development have been found among thirty species of twenty‐eight genera in sixteen orders out of eight classes of vertebrates. In ten species the mesoderm participates in the formation of the hepatic parenchyma.

The ductal system develops in some cases as an outgrowth from the gut; in more cases it develops from liver cells and joins the intestine secondarily.

Von Baer's first and second law of embryogenesis, as well as the biogenetic law of Müller and Haeckel, are contradicted by these observations. New evidence is presented for the non‐specificity of germ layers.
DETOXICATION MECHANISMS IN INSECTS
Authors: SMITH J. N.
Published: January 2008

Information relating to the metabolic alteration, in insects, of foreign organic compounds has been reviewed and is summarized in Table i. The convenient term ‘detoxication mechanisms’ has been retained to describe the reactions involved, although these do not necessarily reduce the toxicity of absorbed substances, and may in some cases produce extremely toxic metabolites. Some of these reactions, however, particularly those which involve conjugations, almost always yield nontoxic products. Although much of the evidence is still unsatisfactory from a chemical standpoint it has become clear that a number of detoxication mechanisms are common to both insects and vertebrates. Nevertheless, the extent to which they occur in different species may vary. One important conjugation mechanism is different in insects and vertebrates, as it has been found that phenols are converted to their ‐glucosides in insects. To this extent insects are more like plants than like vertebrates, in which phenols are detoxified by condensation with glucuronic acid.

Other conjugations, in which phenols are transformed into ester sulphates, aromatic amino groups are acetylated, aromatic acids condensed with glycine and heterocyclic ring nitrogens methylated, are found in both vertebrates and insects.

Very few definite data are available on oxidations of foreign organic compounds in insects, and it is not possible to say whether the mechanisms involved are always the same in insects and vertebrates. What is known of the intermediary metabolism of tryptophan and tyrosine does suggest, however, that there may be a common path for some aromatic hydroxylations.

The products of metabolic oxidation of the thiophosphate and phosphoramide insecticides in vertebrates and insects have been shown to be the same, and these products are much more toxic than the original material.

The data available on the metabolism of DDT (XXXVII) and some related compounds have been summarized. In most insects it is believed that DDT is dehydrochlorinated to an ethylenic compound, DDE (XXXVIII). No evidence has been found that insects form any DDA (XXXIX), the metabolite found in vertebrates, but evidence is accumulating that one or more, as yet unidentified, metabolites of DDT are produced. One of these is very probably some form of conjugate.

In addition to the mechanisms of conjugation, oxidation and dehydrochlorination, several minor processes have been observed in a single species. Aromatic nitro groups are reduced to amino groups, thiocyanate is formed from cyanide and heavy metals may be inactivated by conversion to their insoluble sulphides.

I am grateful to Professor R. T. Williams for discussions and criticisms of the manuscript.
THE HABITAT OF THE EARLY VERTEBRATES
Authors: ROBERTSON JAMES D.
Published: January 2008

On geochemical grounds it seems that the early Ordovician seas were very similar in salinity and ionic composition to seas at the present time. Physiological speculations based on the assumption of dilute sea water in the Ordovician oceans, especially those which relate the level of salts in vertebrate blood to that of these seas, are invalid. The first marine and freshwater vertebrates were probably subjected to the same physicochemical environmental stresses which affect present‐day fishes and the lower marine chordates.

The earliest vertebrate remains are from the Ordovician and include problematical fish‐jaws (from Missouri, U.S.A.), plates and scales of heterostracans and coelolepids (from Colorado, U.S.A.), and teeth of acanthodian fish (from the neighbourhood of St Petersburg, Russia). All these remains are from marine sediments, associated with typical marine invertebrates in the first two cases.

Ostracoderms and placoderms have been found in Silurian strata (including the Downtonian) in eight countries of Europe and in North America. The fossils comprise heterostracans, coelolepids, anaspids, osteostracans, acanthodians and arthrodires. Associated marine invertebrates are found with the vertebrate fossils in the vast majority of the records, and in no case is there any evidence that the ostracoderms and fishes lived otherwise than in the sea.

Ostracoderms and bony fishes are represented in both marine and freshwater deposits of the Devonian period.

A marine origin for the vertebrates is supported by the fact that the three protochordate groups, Hemichordata, Urochordata, and Cephalochordata, are marine.

The members of the marine order Myxinoidea of the Cyclostomata have an internal medium of high salt concentration, equivalent to that of the surrounding sea water, a feature found in the lower chordates and in marine invertebrates. This may well be a primary feature, derived directly from marine chordate ancestors.

Consideration of the glomerular kidneys of the marine myxinoids and elasmo‐branchs, forms with blood isosmotic with sea water, and of the kidneys of other fishes, leads to a rejection of the view that such kidneys are a freshwater adaptation which has arisen in some freshwater protovertebrate. Glomerular kidneys probably existed in marine protovertebrates, and subsequently became a useful preadaptation for life in fresh water.

The arguments deemed to support a freshwater origin of vertebrates have been considered and rejected on the grounds that some are erroneous and others improbable. Palaeontological and physiological evidence leads to the conclusion that the vertebrates were originally a marine group.
THE DERMAL LIGHT SENSE
Authors: STEVEN D. M.
Published: January 2008

1. Dermal light reactions are responses to illumination of the body surface of animals due to stimulation of diffusely distributed photoreceptors.

2. They are found in all major phyla, being most common in aquatic animals with non‐waterproof skins. They are rare in terrestrial arthropods, cephalopods and amniotes.

3. An animal may possess a dermal light sense in addition to eyes or other localized photoreceptors.

4. Responses to dermal stimulation may be local or general, graded or all‐or‐none. They include direct responses to light of some chromatophores, slow orientations by bending movements and many fast withdrawal reflexes.

5. Locomotion in many animals is controlled photokinetically by dermal receptors. The relation between intensity and the speed of locomotion is usually an orthokinesis but in some planarians and the ammocoete larva it is a klinokinesis.

6. There is evidence for orientated control of locomotion by dermal receptors in planarians and some lower vertebrates.

7. Reaction times of dermal responses are relatively long. Except in Metridium, the reaction time consists of a sensitization and a latent period, the relationship between which is complex.

8. Dermal and optic responses exhibit similar physiological characteristics. Dermal light reactions adapt to repeated and continuous stimuli, show considerable powers of dark adaptation and obey Weber's Law over a limited range of intensity.

9. The absolute sensitivity of dermal photoreceptor systems is several thousand times less than that of well‐developed eyes.

10. Action spectra are generally similar to those of eyes, with maximum sensitivity usually between 470 and 530 mμ. The photochemical systems responsible for all light reactions are believed therefore to be of a similar nature.

11. No single receptor system at the cellular level of organization can account for all types of dermal light reactions.

12. There is evidence that the protoplasm of a variety of cells in Metazoa is sensitive to light. The parietal muscles of Metridium, the ectodermal nerve net of Diadema and some types of chromatophores have been found to be light‐sensitive.

13. The light reactions of blind cave‐dwelling teleosts show some unusual features which may be related to a comparatively recent loss of functional eyes.

14. There is no convincing evidence of fundamental differences in the processes responsible for dermal and optic light responses, nor for the existence of more than one type of dermal photoreceptors in any species.

15. A common structural basis for all light reactions, if it exists, must be sought in the fine structure of cells.

I am most grateful to my colleagues who have read the manuscript. I wish to acknowledge my gratitude to Professor P. B. Medawar, F.R.S., for hospitality in the Zoology Department of University College, London, where much of the work on this article was done.
COLEOPTERAN ASSOCIATIONS IN THE BRITISH ISLES DURING THE LATE QUATERNARY PERIOD
Authors: PEARSON R. G.
Published: January 2008

1. The fauna of the climatic optimum of the Eemian Interglacial period contained thermophilous species and as such indicates a climate at least as warm as that today.

2. The Chelford fauna dating from ca. 57,000 years before the present is comparable to that of Finland and Soviet Karelia. An analysis of the Carabidae suggests that within Scandinavia it is comparable with that which occurs at the top of the regio quercina.

3. The Upton Warren fauna contains stenothermal arctic and boreal species and one Uralian species. The Carabidae suggest a comparison with the regio coniferina in Scandinavia.

4. The Fladbury fauna has a large number of stenothermal arctic and boreal species and the Carabidae suggest a comparison with the top of the regio betulina in Scandinavia.

5. The Colney Heath fauna contains stenothermal and stenotopic arctic and boreal species. The Carabidae suggest a comparison with the regio coniferina in Scandinavia.

6. The St Bees fauna only contains a few remains of stenothermal boreal species and there is a considerable change in the percentage representation of the dominant species within the deposit.

7. The stenothermal arctic element largely disappeared from the lowland fauna in a period of some 1600 years during pollen zone I.

8. The thermophilous species immigrated into north‐west Europe in some 3000 years between pollen zones III and VII.

9. Heliophilous species are well represented in Full‐ and Late‐glacial deposits. Their present restricted distribution is the result of Post‐glacial afforestation.

10. Halophilous species have undergone a restriction in their range comparable to that of the heliophilous species.

11. It is possible that certain observed distributional anomalies previously thought to result from glacial survival and subsequent extension of range may be the result of Post‐glacial survival in areas where there was only limited afforestation.

12. During the late Quaternary era the changes in the distribution of the beetles parallel those of the angiosperms and gymnosperms.

13. In terms of the Full‐, Late‐ and Post‐glacial periods the terminocratic grouping includes boreo‐alpine, northern oceanic, eurythermal and heliophilous species. The mediocratic grouping includes southern continental and oceanic eurythermal species.
PHOSPHATES AS CRYSTAL POISONS OF CALCIFICATION
Authors: SIMKISS K.
Published: January 2008

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.
MICRO‐ORGANISMS and SOIL STRUCTURE
Authors: GRIFFITHS ELLIS
Published: January 2008

1. Experimental analysis of the influence of micro‐organisms on soil structure has been confined to aggregation, i.e. the formation of small clusters of soil particles which are resistant to the disintegrating action of water.

2. Aggregation is influenced by the mineral constituents of the soil, notably clay, but organic matter is considered to be most important.

3. Decomposition of organic matter regularly leads to increased aggregation in non‐sterile soils. Under sterile conditions (i.e. in the absence of micro‐organisms) no increase in aggregation is observed, so that it is evident that micro‐organisms are implicated in this process.

4. Investigations of the role of micro‐organisms have been concerned with two possible effects: (1) the action of filamentous organisms (particularly fungi) in mechanically entangling soil particles to form stable aggregates, and (2) the action of products of micro‐organisms (of all groups) which may cement soil particles together.

5. In most soils the mycelium of filamentous organisms (fungi and actinomycetes) is only present for relatively short periods so that aggregation produced by them tends to be ephemeral. In sandy soils, however, mycelium appears to be more persistent and hence of greater significance. Since fungi are commonly associated with the early stages of decomposition of plant remains, it is suggested that they may also be important in situations where plant residues are regularly being added to the soil, e.g. grassland and forest.

6. Of the many compounds produced by micro‐organisms, most attention has been given to extracellular polysaccharides. These are produced by many soil organisms and can be shown to be effective aggregating agents. Compounds of similar character have been demonstrated in natural soils but satisfactory methods for their quantitative estimation have not been developed. Consequently their contribution to aggregation cannot be accurately evaluated. Evidence so far presented, does, however, indicate that in many cultivated soils they make a considerable contribution.

7. In old grassland and forest soils, extraction of polysaccharide by periodate oxidation appears to have little or no effect on aggregation and in these cases aggregation would seem to be due to other components of the soil organic matter. Although this may well be so, it is also suggested that the distribution pattern of organic materials in the soil may be an important contributory factor. Certain materials, e.g. lipids, though not effective as aggregating agents when mixed with the soil, increase stability when sprayed on the surface of unstable aggregates. The significance of such effects has not so far been critically examined.
THE RELATIONSHIP BETWEEN BLUE‐GREEN ALGAE AND BACTERIA
Authors: ECHLIN P. , MORRIS I.
Published: January 2008

Recent studies of bacteria and blue‐green algae in the electron microscope have shown striking similarities in the basic cellular architecture of the two groups. This evidence has been presented in detail above and may be summarized as follows:

(I) The cell envelope of blue‐green algae bears a superficial resemblance to the cell wall of bacteria, particularly to the Gram‐positive organisms. Like bacteria, blue‐green algae also possess a mucopeptide component as an important part of the cell wall. However, the composition of this mucopeptide component resembles more closely that of Gram‐negative bacteria, though more species of blue‐green algae need examination before the relationship can be established with any certainty.

(2) The older distinction between the chromatophores of photosynthetic bacteria and the lamellae of blue‐green algae has been shown to be superficial. In both forms the essential feature of the photosynthetic apparatus is a pair of membranes enclosing a space; this may be large in bacterial chromatophores or small in ‘true’ lamellae. This basic structure is seen in higher plants where the lamellar systems are enclosed in a membrane‐bounded structure, the chloroplast. No such membrane isolates the photosynthetic machinery of bacteria and blue‐green algae.

(3) No membrane isolates the nuclear material of blue‐green algae or bacteria. The nucleoplasm of these two groups is structurally similar and show the same morphological changes with variations of fixative treatment.

(4) Both bacteria and blue‐green algae lack mitochondria, true vacuoles and an endoplasmic reticulum. Membranous structures (mesosomes) are widespread in bacteria and recently similar structures have been seen in blue‐green algae.

(5) The nucleoplasm presumably divides by an amitotic process, as no stages of mitosis or meiosis have been observed in either group. The cell division in blue‐green algae shows a superficial resemblance to that of Gram‐positive bacteria.

Recent observations on the cytoplasmic inclusions of the two groups have been presented above, but no pattern has yet emerged. The spores of the two groups have also been discussed and the little detailed observation available supports earlier suggestions of some important differences between the two groups.

Bacteria and blue‐green algae also resemble each other and differ from other organisms in their method of ornithine biosynthesis, their apparent absence of sterols and their sensitivity to certain antibiotics.

The evidence here summarized supports the suggestion that bacteria and blue‐green algae should be isolated in a group distinct from all other organisms. Two speculative aspects of the problem have been discussed: their evolutionary relationship with other organisms and with each other. With regard to the latter, it seems probable that bacteria and blue‐green algae arose from a common ancestor, since it is unlikely that so many features common to the cells of both groups arose independently more than once.
STRUCTURE AND FUNCTION OF MAMMALIAN TENDON
Authors: ELLIOTT D. H.
Published: January 2008

1. Tendons are a specialized form of connective tissue uniting muscle and bone and as such have functions essential to normal mobility.

2. The structural unit of tendon is the fibre, up to 300 µ in diameter, consisting of fibrils of collagen, encircled by the anastomosing processes of fibroblasts. Fibres are arranged in fasciculi but may pass from one to another so that successive cross‐sections show slightly different appearances. Such interweaving ensures the equal distribution of muscular tension over the whole area of insertion, particularly where the movement of a joint alters the angle between tendon and bone.

3. There are two hypotheses concerning the nature of the muscle‐tendon junction. First, the tension developed within a muscle fibre might be transmitted to the helical perisarcolemmal fibres of connective tissue surrounding its length and thence to the tendon, and secondly, and more probably, the tension might be transmitted directly from the end of the myofibrils to the interdigitating fibrils of the tendon. The interdependence of muscle and tendon is further illustrated by their longitudinal growth since the changing length of the muscle belly relative to the distance between the bony attachments determines the rate of growth and relative length of tendon.

4. The orientation of fibrous tissue in the tendon supports the hypothesis of a mechanical influence upon tendon growth, but there is no strict relationship between muscle strength and tendon thickness and various muscles differ in the ratio of their total fascicular cross‐sectional area to tendon thickness. It would appear that this difference develops post‐natally and, since a red postural muscle has a relatively thick tendon, it has been suggested that the duration as well as the level of transmitted tension might influence the growth of collagen.

5. Tendon thickness may increase proportionately with muscle cross‐sectional area in conditions which cause the muscle to hypertrophy, but when the muscle is de‐nervated or excised in the young animal growth of tendon thickness occurs in such a manner as to suggest that the growth of collagen is determined by the history of the total tension transmitted.

6. The tendon has a tensile strength which is probably four times as great as the maximum tension that it has to transmit in vivo and an even greater margin of safety is present in penniform muscles which transmit less maximum isometric tetanic tension per unit fascicular cross‐sectional area than do fusiform muscles. Although the wave form seen on the surface of a tendon when at rest is eliminated by less than 10 % of the maximum tension which its muscle is liable to transmit, it is possible that the normal range of tensions transmitted in vivo might fall within that part of the stress‐strain curve where the tendon is still easily extensible.
ENVIRONMENTAL AND BIOCHEMICAL CONTROL OF STOMATAL MOVEMENT IN LEAVES
Authors: ZELITCH I.
Published: January 2008

The chloroplasts of guard cells are largely responsible for the response of stomata to light. The opening movement is probably associated with the synthesis of ATP by non‐cyclic photophosphorylation, and the obligatory fixation of carbon dioxide to produce glycolic acid. The oxidative metabolism of glycolic acid is related to ATP synthesis as well as to the possible formation of carbohydrate. In the absence of oxygen in the gas phase, stomata open poorly, and the synthesis of glycolic acid is also inhibited. α‐Hydroxysulphonates, which are inhibitors of glycolate oxidase, prevent stomatal opening in a competitive manner. High concentrations of carbon dioxide close stomata and inhibit the formation of glycolic acid, and the effect of high carbon dioxide on closing can be reversed by providing the tissue with glycolic acid.

When leaf hydration is not limiting, raising the temperature in the environment causes an increase in the steady state of the stomatal aperture. There is little effect of temperature on the rate of closing in darkness, hence opening is the active process.

A large number of chemical inhibitors were found to prevent opening, either by interfering with metabolic reactions in the guard cells concerned with the ‘pump’ responsible for the increased turgidity, or by acting on the membranes that serve as a ‘check valve’. Sodium azide is a substance which acts by both mechanisms, but the maximal effect occurs at different concentrations, and experiments with this inhibitor have shown that the opening and closing reactions operate independently.
STOMATAL RESPONSES TO ILLUMINATION
Authors: MEIDNER HANS , MANSFIELD T. A.
Published: January 2008

1. Stomata have been found to respond to small changes in carbon dioxide concentration within the leaf, and movements due to illumination, temperature, leaf‐water content, or metabolic inhibitors can be explained, at least in part, by their affecting the internal carbon dioxide concentration. This is confirmed by the fact that effects of such factors can be reversed experimentally by flushing the leaf with air of an appropriate carbon dioxide content. We conclude that changes in carbon dioxide concentration set in motion reactions affecting guard cell turgor relations (see 8 below).

2. The photosynthetic production of carbohydrates, or of intermediates in their synthesis such as glycollic acid, does not seem to have any major effect on guard cell turgor, which can readily change in the absence of photosynthesis in darkness in response to different carbon dioxide concentrations. Factors which affect photo‐synthetic production ordinarily affect the internal carbon dioxide concentration and it is the latter which is more directly involved in changing guard cell turgor relations.

3. In addition to the effects of environmental factors on carbon dioxide concentration, light (blue), temperature and leaf water content may also affect guard cells independently of carbon dioxide. Whether such effects are due to hydrolysis of starch or another polysaccharide, or to changes in permeability or quite another mechanism, is not known.

4. As well as being effected by the environment, stomatal movements are under the control of endogenous rhythms in light and darkness. Rhythms can produce opening in darkness and partial closure in light, and hence can modify or overrule the response to external factors. However, the phase of the rhythm does come under the control of the environment through a low‐intensity light reaction sensitive to red and far‐red wavelengths. This light reaction is quite distinct from those directly concerned in the production of stomatal opening.

5. Stomatal behaviour in cacti and other succulents is at first sight practically the opposite of that in other plants, in that they open at night and close during the day. We suggest that this type of behaviour may, however, be a relatively simple development from the normal pattern.

6. Stimuli affecting the stomata can be transmitted within a leaf, or from one part of a plant to another. The mechanism of the transmission is not known, but it could be brought about by a chemical substance which is translocated.

7. There is evidence that the processes of stomatal opening and closing are different in nature, and that one is not simply a reversal of the other. It is probable that an active (oxygen‐requiring) mechanism in involved in stomatal opening. Stomata come under the control of so many factors, both external and internal, that several processes are likely to contribute to the turgor changes which bring about their movements.

8. The mechanism of carbon dioxide control over stomata is not known.
SELECTION, PREDICTION AND RESPONSE
Authors: LEE B. T. O. , PARSONS P. A.
Published: January 2008

1. The biometric approach to selection experiments has been outlined, and found to be rather deficient because it is based on excessively restrictive models which cannot take into account the complex architectures of quantitative traits as are being revealed today.

2. The nature of polygenes is discussed in detail from the theoretical point of view. In out breeding species, some form of the balanced polygenic complex is likely, showing polymorphism for the constituent genes. Although polymorphism is implicit in the argument, definitive evidence for poiymorphisms has only just appeared.

3. There is no evidence that polygenes differ from any other gene.

4. Several artificial selection experiments are described, in particular in Drosophila. By means of appropriate breeding techniques after obtaining responses to selection, genetic activity controlling quantitative traits can be located to chromosomes, and even specific loci found. Such few studies as have been carried out reveal, in general, the types of genetic architecture predicted on theoretical grounds.

5. Selection for behavioural traits is considered briefly and it appears that no new principles are needed, except that careful environmental control and objective measurement present problems.

6. The results of selection for quantitative traits in micro‐organisms reveal similarities to results in higher organisms in the few cases where definitive work has been carried out.

7. Work on the simulation of models by computers has not greatly advanced selection experiment theory, mainly because, with few exceptions, linkage has been ignored.

8. The existing theory on which selection experiments are based is inadequate for several reasons. It cannot predict the rate of response to selection nor the ultimate limits to selection, the nature of correlated responses to selection, nor the nature of gene segregation underlying the observed variability.

9. Strains set up from single inseminated founder females from the same population of Drosophila have been shown to differ genetically for several quantitative traits. Therefore the base population is polymorphic for genes controlling these traits. This was exploited by carrying out directional selection on lines derived from those strains showing a high incidence of scutellar chaetae. This led to far more rapid responses to selection than lines derived from strains where the incidence of scutellar chaetae was lower.

10. Ultimately, one can envisage the selection experiment as it is known today being partly replaced by the manipulation of located genes controlling quantitative traits into certain combinations.
ENVIRONMENTAL AND BIOLOGICAL CONTROLS ON BIVALVE SHELL MINERALOGY
Authors: KENNEDY WILLIAM JAMES , TAYLOR JOHN DAVID , HALL ANTHONY
Published: January 2008

Bivalves lay down two forms of calcium carbonate in their shells, aragonite and calcite. Shells may be wholly aragonitic, or may contain both aragonite and calcite, in separate monomineralic layers. Shells are built up of several layers of distinct aggregations of calcium carbonate crystals. These aggregations are referred to as shell structures and their general features are described. Aragonite occurs as prismatic, nacreous, crossed‐lamellar, complex crossed‐lamellar and homogeneous structures. Calcite occurs as prismatic or foliated structures. Myostracal layers (calcium carbonate laid down below sites of muscle attachment) are always aragonitic. The ligament and byssus when calcined are also invariably aragonitic. A summary of the occurrence of calcite and aragonite and the associated shell structures is given. Calcite is found only in the outer layer of superfamilies belonging to the subclass Pterio‐morphia with the exception of two species only from the Heterodont superfamily Chamacea. Generally within a superfamily shell structure and mineralogy are very constant. In all superfamilies these combinations have existed for many millions of years.

It is therefore demonstrated that the prime control on shell mineralogy is genetic. Possible controls on mineralogy by the mantle cells, nature of the extrapallial fluid, nature of the periostracum and the organic matrix of the shell layers are discussed.

It is known that environmental factors may modify the basic mineralogy/shell structure pattern within a superfamily. Thus there is an inverse relationship between the percentage of calcite in the shell and the mean temperature of the environment inhabited by the bivalve.

A critical examination of published data shows that the evidence is convincing only in the superfamily Mytilacea. The species Mytilus californianus, which shows the greatest temperature effects, is peculiar amongst the Mytilacea in having an inner calcite layer as well as an outer one.

Conflicting evidence for an inverse relationship between salinity and aragonite content is reviewed. The differences of opinion cannot be resolved without experimental work.

We are grateful to the following for much useful discussion, and encouragement in many ways: Dr J. R. Baker, Dr G. E. Beedham, Dr B. C. M. Butler, Dr A. Hallam, Dr J. D. Hudson, Dr R. P. S. Jefferies, Mr J. Macrae, Dr W. S. McKerrow, Mr N. J. Morris, Mr C. P. Palmer, Mr N. Tebble, Dr E. R. Trueman and Professor A. Williams. Our best thanks are to Mr R. Cleevley for critically reviewing the manuscript.

The following have rendered us considerable technical assistance: the staff of the electromicroscopy unit of the British Museum (Natural History), under the direction of Mr B. Martin; the technical staff of the Department of Geology, King's College, London and of the Department of Geology and Mineralogy, Oxford; Mrs J. M. Hall, and Mr G. Burton.
THE HETEROMORPHS AND AMMONOID EXTINCTION
Authors: WIEDMANN JOST
Published: January 2008

The heteromorph ammonoids are quoted as a favourite example of degeneration and the decline of a Bauplan‘condemned’ to extinction. With astonishing tenacity this view of the heteromorphs as ‘phylogenetic end‐forms’ has embedded itself in the palaeontological literature and is still current. This is contradicted by the most recent investigations, directed especially at the Cretaceous heteromorphs, which necessitate correction of the typolysis concept as well as modification of the most uncontested of the phylogenetic ‘laws’, Dollo's ‘law of irreversibility’. Contrary to the usual textbook hypothesis, the heteromorphs return in several evolutionary lineages to normal coiling of the shell and, in general, to a phylogenetically older type of suture line. At the same time these results encourage fresh reflexion on possible exogenous causes of phylogenetic extinction of the ammonoids. A clear causal connexion exists between this extinction and the far‐reaching epirogenic changes in sea level in the late Cretaceous; cosmic explanations are unnecessary.

In conclusion it may be added that the precipitate formulation of phylogenetic ‘laws’ and ‘principles’ based on too little basic information has encumbered this branch of palaeontology with a stifling set of prejudices rather than providing it with guide lines crystallized from long experience and observation. It is vitally necessary in the interests of palaeontology that interpretation and observation be separated far more than has been the case in the past.
THE BIOCHEMICAL ROLE OF NATURALLY OCCURRING POLYAMINES IN NUCLEIC ACID SYNTHESIS
Authors: STEVENS LEWIS
Published: January 2008

1. The polyamines, putrescine, spermidine and spermine occur in free or acetylated form in a wide variety of living organisms. Putrescine is biosynthesized from ornithine or arginine; spermidine and spermine from methionine and either ornithine or arginine.

2. It is difficult to determine the intracellular distribution of polyamines since they are all very soluble in water and they are readily redistributed when cells are disrupted. Evidence suggests that a substantial proportion of the intracellular polyamines is attached to the ribosomes and that spermidine is not concentrated in the nucleus.

3. Polyamines bind strongly to both DNA and RNA. The strength of binding is:spermine > spermidine > putrescine. Polyamines stabilize the double helix of DNA, probably by forming a bridge across the narrow groove, by involving electrostatic bonding with the phosphate group. However, they do not appear to alter the overall conformation of DNA. Spermine enables single‐stranded RNA to fold into a more compact configuration which is less susceptible to attack by ribonuclease.

4. Spermine and spermidine are able to stimulate the DNA primed RNA polymerase. They facilitate the removal of RNA from the DNA‐RNA‐enzyme complex.

5. Polyamines promote the association of ribosomal subunits and also the binding of amino acyl transfer RNA to ribosomes. They cause increased coding ambiguities in the process of translation in certain bacterial systems.

6. There is a close correlation between the intracellular concentration of spermidine and the rate of RNA synthesis both in rat liver and in Escherichia coli. Conditions which affect the rate of RNA synthesis also affect the concentration of free intracellular spermidine.

7. Bacteria usually contain putrescine and spermidine, whereas animal tissues contain spermine and spermidine. Spermidine probably fulfils the same role in both bacteria and animal tissues, but the presence of spermine, which is common to eucaryotes, is possibly associated with their more complex mechanisms for regulating RNA and protein synthesis.
BIOCHEMICAL AUTONOMY OF HIGHER PLANT CHLOROPLASTS AND THEIR SYNTHESIS OF SMALL MOLECULES
Authors: GIVAN CURTIS V. , LEECH RACHEL M.
Published: January 2008

1. Mature chloroplasts are able to synthesize a wide variety of compounds of low molecular weight in addition to carbohydrates.

2. Mature chloroplasts from higher plants can synthesize fatty acids from acetate, and galactolipids from UDP‐galactose; but, thus far, there is no direct evidence that chloroplasts can produce their principal fatty acid, α‐linolenate, independently of the rest of the cell.

3. Chloroplasts possess the enzymic machinery necessary to generate most of the common amino acids from inorganic nitrogen plus appropriate a‐keto analogs of amino acids. However, the plastids do not appear able to synthesize many α‐keto carbon compounds from the initial products of photosynthetic carbon dioxide fixation.

4. Whether chloroplasts can generate their own supply of acetate remains in doubt.

5. There is little evidence for or against the existence of chloroplastic enzymes catalysing synthesis of purines and pyrimidines.

6. Recent evidence confirms that immature plastids possess the complement of enzymes required for synthesis of protochlorophyllide from 8‐aminolaevulinic acid but leaves open the possibility that extrachloroplastic cofactors may be involved in protochlorophyllide biosynthesis.

7. The weight of the available evidence suggests that, despite its great metabolic versatility and possible reproductive autonomy, the chloroplast of the higher plant is not metabolically autonomous or nutritionally independent of the remainder of the plant cell. Therefore, if there is any validity to the oft‐repeated speculation that chloroplasts have evolved from ancient free‐living procaryotes, it appears that the evolution of the chloroplast has led to a considerable loss of nutritional autonomy concomitant with the development or preservation of photosynthetic competence.
X‐CHROMOSOME INACTIVATION AND DEVELOPMENTAL PATTERNS IN MAMMALS
Authors: LYON MARY F.
Published: January 2008

1. The review considers information from mammalian embryology relevant to X‐chromosome inactivation, and from X‐inactivation relevant to mammalian embryology.

2. Properties of the inactive‐X, by which it may be recognized are: sex chromatin, heteropycnosis, late replication and the absence of gene product. Each of these has advantages and disadvantages in particular circumstances. In some species the X carries constitutive heterochromatin, which must be distinguished from the facultative region.

3. The time of X‐chromosome inactivation can be estimated from the time of appearance of sex chromatin or late replication, or inferred from the appearance of heterozygotes for X‐linked genes or of experimental chimaeras. The estimated time varies with species, and in the mouse and rabbit is near the time of increase in RNA synthesis.

4. Whereas in eutherian mammals either the maternally or the paternally derived X may be inactivated in different cell lines, in marsupials the paternal X is always the inactive one.

5. During development various factors act to distort the patterns produced by random X‐inactivation. These factors include cell selection, transfer of gene product, and migration and mingling of cells.

6. There is no clear evidence that X‐chromosome inactivation is not complete.

7. In female germ cells both X‐chromosomes appear to be active. In male ones both X and Y appear inactive during most of spermatogenesis, although probably in early stages all X chromosomes present are active.

8. The active and inactive X‐chromosomes may be differentiated by presence or absence of some non‐histone protein or other polyanionic substance.

9. If the genes concerned in synthesis or attachment of this substance are on the X‐chromosome then the differentiation will be self‐maintaining.

10. The initiation of the differentiation requires either the attachment of different X‐chromosomes to different sites, or some interaction of X‐linked and autosomal genes, concerned in inducing or repressing activity. Some possible models are discussed.
EVOLUTION OR REVOLUTION OF AMMONOIDS AT MESOZOIC SYSTEM BOUNDARIES
Authors: WIEDMANN JOST
Published: January 2008

1. Biological revolutions at major stratigraphical boundaries have been given numerous explanations involving endogenous biological, exogenous ecological, physical, and cosmic, as well as sedimentary or chemical factors. In an attempt to elucidate the true nature of these faunal revolutions and to assess the possible influence of biological and/or physical factors, the evolution of ammonites at the boundaries of Mesozoic stratigraphical Systems is reviewed. It is believed that the more detailed data now available can give a clearer impression of evolutionary events at these boundaries.

2. It can be demonstrated that there is neither an abrupt and world‐wide extinction, nor a spontaneous replacement by new elements at these caesuras as had been generally supposed to have occurred at the Triassic‐Jurassic boundary, for example. Instead, one can recognize three distinct phases in the sequence of events: (1) a continuous disappearance of the ‘antique’ faunal elements; (2) a similarly continuous, gradual, and largely synchronous appearance of, or substitution by, qualitatively distinguishable ‘modern’ elements in small populations, yet in various parallel lineages (mosaic evolution); (3) a quite revolutionary, and quantitatively very sudden, diversification of these new elements, occurring at or with some delay above the boundary.

3. Thus one can demonstrate both continuous evolution of the modern faunas (‘preadaptational phase’), as well as ‘discontinuous’ spontaneous revolution, which does not produce qualitatively new characters and must be explained by diversification or adaptive radiation. This means that no further explanation by internal factors or by higher mutation rates resulting from the impact of cosmic rays becomes necessary. It is believed that, preceded by high extinction rates, world‐wide ecological factors promoting higher niche diversity suffice to explain these adaptive radiations. The high degree of provincialism, endemism and specialization of the ‘antique’ faunas and the constant survival of smooth oxycones — regarded as inhabitants of a deep‐sea environment — demonstrate that marine regressions and transgressions were the most effective ecological factors.

4. If there is not too much time involved between the two events, the caesura (Faunenschnitt) between final extinction of the old faunas and the radiation of the new is the most appropriate point by which to define System boundaries.