bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE HETEROMORPHS AND AMMONOID EXTINCTION
Authors: WIEDMANN JOST 
Published: January 2008

SummaryThe 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

Summary1. 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

Summary1. 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

Summary1. 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

Summary1. 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.
THE STRUCTURE OF FISH GILLS IN RELATION TO THEIR RESPIRATORY FUNCTION
Authors: HUGHES G. M. , MORGAN MIRIAM 
Published: January 2008

Summary1. The general structure of the gills of different fishes is compared and it is concluded that, though essentially the same, there are certain differences by which they can be recognized. Possible ways in which they may have evolved from one another are considered.2. A detailed account is given of the structure of the secondary lamellae, where gaseous exchange takes place, and it is shown that two epithelial sheets are separated by a vascular axis mainly composed of pillar cells overlain by a basement membrane on each side. Blood pathways through the gills are discussed in relation to their respiratory function.3. The embryonic development of gills is described and evidence regarding homo‐logies of different structures, particularly the pillar cells, is reviewed.4. The gills of fish having different modes of life show variations in (a) the number of arches, (b) the number and length of the gill filaments, and (c) the size and frequency of the secondary lamellae. Ways in which measurements of gill area may be carried out and some of the complications involved are reviewed and a summary given of measurements made for a wide variety of species. Measurements of the thickness of the water‐blood barrier are also discussed; the more active fish generally have thinner water‐blood barriers and larger gill areas.5. The different mechanisms of gill ventilation are summarized and characteristics of gill resistance in elasmobranchs and teleosts are compared. Gas exchange is discussed in relation to available techniques and the current terminology and symbols, and to indicate the value of analogies between gill exchangers and systems studied by engineers.6. It is outlined how studies of the functioning of gills during coughing, parasitic infection, and in polluted waters add to knowledge of their role in respiration.
THE PRODUCTION OF PARTHENOGENETIC MAMMALIAN EMBRYOS AND THEIR USE IN BIOLOGICAL RESEARCH
Authors: GRAHAM C. F. 
Published: January 2008

Summary and Conclusions1. The eggs of many mammalian species show signs of early parthenogenetic development as they age after ovulation and oocytes may form transplantable terato‐carcinomas. These cases of apparently spontaneous parthenogenetic development suggest that the cells of the female germ line have an inherent tendency to divide and differentiate.2. The ovulated eggs of virgin female mammals may be stimulated to start parthenogenetic development by a wide variety of treatments. Most of these damage the egg so that it does not develop beyond the 4 cell stage. However if the eggs are exposed to electrical activation, hyaluronidase treatment, or temperature shock then in many cases they will develop into blastocysts.3. These blastocysts may be either haploid or diploid. Haploid blastocysts may be formed either by the egg extruding the nucleus of the second polar body or by the egg dividing in half, so that the female pronucleus is in one cell and the nucleus of the second polar body is in another cell. Diploid blastocysts are formed by the retention of the nucleus of the second polar body within the egg. The way in which the egg develops may be controlled by altering the osmolarity of the culture medium, the age of the egg at the time of activation, or the strain of animal used.4. The action of the sperm on the egg can be defined by comparing the events of normal fertilization and parthenogenetic activation. Both these stimuli cause the egg to expose binding sites for Concanavalin A to synthesize DNA and to divide. However, the release of cortical granules, which occurs after fertilization, does not appear to be induced by parthenogenetic activation, and it is significant that parthenogenones lack the sperm nucleus and mitochondria.5. The majority of parthenogenones die soon after implantation. Death at this time occurs with parthenogenones obtained from the activated eggs of both inbred and outbred stocks. Death might be caused by recessive lethal mutations or by extra‐genetic effects of the maternal chromosomes.6. Parthenogenones contain endogenous A‐type particles which shows that these bodies are inherited through the female germ line.7. Parthenogenones may in the future provide both a method for chromosome mapping and a source of haploid cells.At present the use of mammalian parthenogenones in biological research is restricted by the heavy embryonic losses which occur around the time of implantation. This means that the role of the sperm, gene activity and virus expression must be studied during a very limited period. Part of the mortality before implantation is the consequence of the damage which the egg suffers during activation and it should be possible to reduce this loss by improving the techniques for activation. It may also be possible to increase the quantity of cells derived from haploid and diploid mammalian embryos by deriving teratocarcinomas from them.
TEMPERATURE ACCLIMATION AND THE NERVOUS SYSTEM
Authors: LAGERSPETZ KARI Y. H. 
Published: January 2008

Summary1. The conduction velocity of the compound action potential of peripheral nerves shows compensatory acclimation to temperature in a fish, a snail, a crab, and probably also in the frog. The heat and cold tolerances of peripheral conduction are probably both increased by cold acclimation in the frog.2. The properties of compound action potentials are not suitable for temperature acclimation studies, since different neuronal populations in the same nerve have been found to exhibit different temperature characteristics.3. Single but septate giant nerve fibres of earthworms show compensatory temperature acclimation of the conduction properties, the form of the action potential and of the axonal cable properties, especially below 13–19 °C.4. The fatty acids and the plasmalogen aldehydes of the phospholipids of the goldfish brain are more unsaturated at lower acclimation temperatures.5. The Na+‐K+ ATPase activity of the earthworm nerve cord shows compensatory acclimation at low temperatures.6. The spontaneous activity of the central nervous system of insects is altered in a compensatory manner by temperature acclimation. In fish, the cold tolerance of simple and complex reflexes and of conditioning is adaptively altered by temperature acclimation. The role of the central nervous system, especially of the thermoregulatory centre, in the temperature acclimation of homeotherms is established.7. There are adaptive isoenzymes of acetylcholinesterase in the brain of the rainbow trout. These isoenzymes differ from each other in respect of the temperature dependence of their enzyme‐substrate affinity. The synthesis of acetylcholine receptor molecules may also be affected by temperature acclimation.8. The metabolism of putative synaptic neurotransmitters (5‐hydroxytryptamine, adrenaline, noradrenaline) is altered in the frog and mouse brains during the early phases of temperature acclimation. These changes may initiate the physiological processes connected with temperature acclimation.9. The neuromuscular transmission in the frog shows after acclimation to cold, increased resistance to it and some indications of temperature compensation.10. Changes in neurosecretion seem to be involved in temperature acclimation both in poikilotherms and homeotherms. The fast axonal transport of proteins shows compensatory acclimation to cold in the frog.
HORMONAL REGULATION: MORPHOGENETIC AND ADAPTIVE SYSTEMS
Authors: CSABA G. 
Published: January 2008

Summary1. The endocrine glands of vertebrates develop from all three germ layers; those arising from ecto‐ and endoderm produce hormones of an amino‐acid or polypeptide‐type, while those arising from the mesoderm secrete hormones of a steroid nature.2. All mesodermal glands and a single endodermal gland, the thyroid, are under hypophyseal control.3. All pituitary‐controlled endocrine glands act upon morphogenetic processes after a certain stage of phylogenesis, and the same applies to the directly‐acting hypophyseal hormone STH. It follows that the pituitary acts not so much as the ‘conductor of endocrine glands’ in general, but as the central regulator of morphogenetic processes in particular.4. Incorporation of the thyroid gland into the morphogenetic system took place at the phylogenetic level at which its morphogenetic role came to the fore in processes of metamorphosis.5. The other main hormone system, the adaptive system, includes all endocrine glands of ecto‐ or endodermal origin. These account for short‐term homeostatic regulation and depend on the pineal body for higher control.6. While hypophyseal regulation is stimulatory and is operated through a precise feed‐back mechanism, regulation by the pineal body is more primitive and inhibitory, with minimal indications of feed‐back. The influence becomes stimulatory only in those instances in which the target glands are controlling the same function in an opposite manner, e.g. the parathyroid and the C‐cell. The pineal influence also inhibits the function of the thyroid, and hypophyseal stimulation becomes superimposed on this inhibitory effect, in accordance with an actual requirement.
NUCLEAR GLYCOCONJUGATES AND THEIR RELATION TO MALIGNANCY
Authors: STODDART R. W. 
Published: January 2008

Summary1. The nucleus has a distinctive carbohydrate chemistry, the main features of which are the lack of glycosphingolipid, the high density of carbohydrate per unit area of nuclear membrane, the presence of glycosaminoglycan in the nuclear matrix and possibly the nuclear membranes, and the existence of glycosylated non‐histone proteins.2. The nucleus has considerable autonomy in its metabolism of glycosaminoglycan and has a capacity for glycosyl transfers involving glycosyl dolichyl phosphates and pyrophosphates. This latter activity probably resides in the nuclear membranes.3. The soluble fraction of the nucleoplasm contains the total cellular CMP‐sialic‐acid synthetase and, hence, all sialic acid metabolism passes through the nucleus, which may have a regulatory role. Uncertainty remains as to the sialic acid content of the glycoproteins of the nucleus and it is likely to vary between cell types.4. Malignancy is associated with several alterations in the glycosylation of nuclear membranes, including increased levels of sialic acids in the glycoproteins of the inner nuclear membrane: changes in glycosylation of the matrix and chromatin are not yet well defined. In malignancy, some nuclear glycoproteins may possibly appear in other cellular membranes.
TISSUE CULTURE IN THE PRODUCTION OF NOVEL DISEASE‐RESISTANT CROP PLANTS
Authors: BRETTELL R. I. S. , INGRAM D. S. 
Published: January 2008

Summary1. Plant tissue cultures form the basis of a number of techniques which have been developed to effect genetic changes in plants. Progress is being made in the application of these techniques in breeding new, disease‐resistant cultivars.2. It is possible to induce and select for mutants among populations of cultured plant cells. Novel disease‐resistant plants of a small number of species have been regenerated from cells selected in culture for their resistance to toxins produced by pathogens, both with and without prior exposure to mutagens. It is not known whether such procedures are widely applicable, and the nature of the genetic changes involved has not yet been determined.3. The tissues of plant species which are propagated vegetatively are normally genetic mosaics with regard to many characteristics, including resistance to disease. Thus, some of the plants regenerated from cultured cells of such species are more resistant to pathogens than the parent plants. Novel plants produced in this way are already being used in some breeding programmes.4. Many attempts have been made to modify the genomes of cultured plant cells by means of exogenous nucleic acids. The evidence for integration and replication of this genetic material is equivocal. The technique, therefore, offers no immediate prospects for the development of novel disease‐resistant plants, but may be important in the long term as methods are perfected for using plasmids and other agents as carriers of useful genes.5. Steady advances are being made in producing somatic hybrids of crop plants by fusion of isolated protoplasts. In the long term it may be possible to use protoplast fusion to transfer desirable disease‐resistance traits between related species which cannot be hybridized by conventional breeding methods.6. The culture of excised embryos may be used to grow interspecific and inter‐generic hybrid plants in cases where incompatibility occurs after normal fertilization. The technique is already being used by breeders in the production of disease‐resistant hybrids of crop species.7. It is concluded that tissue culture has a limited but useful role to play in the development of novel disease‐resistant crop plants.