bluuebunny/crossref_metadata_2025 huggingface dataset:
THE STRUCTURE OF FISH GILLS IN RELATION TO THEIR RESPIRATORY FUNCTION
Authors: HUGHES G. M. , MORGAN MIRIAM
Published: January 2008

1. 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 Conclusions

1. 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

1. 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

1. 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

1. 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

1. 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.
ISLAND POPULATIONS OF RODENTS: THEIR ORGANIZATION AND FUNCTIONING
Authors: GLIWICZ JOANNA
Published: January 2008

1. Data from 14 confined populations living under natural conditions (mainly on small islands) and from a few laboratory populations have been used.

2. Several differences between a typical, confined rodent population (i.e. living under natural conditions in a well isolated, homogeneous and relatively small area) and an open one have been determined.

3. Island populations are characterized by:

(a) Attainment and maintenance of high densities not observed at all, or recorded only periodically, in open populations of comparable species.

(b) Stability of population numbers, expressed either by very slight fluctuations or by a very regular cycle with only small differences between peaks of consecutive years.

(c) Lack of emigration resulting from any or all of the barriers surrounding the confined population, from homogeneity of the habitat enclosed by these barriers, or from a lower tendency to dispersal of individuals forming such populations.

(d) Decreased reproduction.

(e) Low losses of independent individuals.

(f) Mortality of sucklings changing with the population density.

(g) An age structure that is probably more differentiated and more regularly changing in an annual and long‐term cycle.

(h) Different spatial organization based on smaller home ranges, that are differently arranged in relation to one another from those in open populations; the arrangement of home ranges allows the population to squeeze in a greater number of individuals with possibly the lowest number of interactions between individuals.

4. In confined populations there must be different mechanisms for the regulation of numbers from those in open populations: (I) in the latter the regulation occurs by the outflow of the surplus of independent individuals, i.e. through the dispersal and high mortality of migrants; (2) in confined populations the inflow of independent individuals is regulated by controlled reproduction and early mortality of offspring. Both mechanisms are induced by social pressure but in the second case (regulation of inflow) a much stronger social organization is indispensable Only those species that are capable of the formation of such an organization can survive as confined populations.

5. Knowledge of phenomena occurring in confined populations is useful for predicting the fate of populations of different species which become isolated as a result of human activity in transforming and subdividing the natural environment.
CUTICULAR LIPIDS OF TERRESTRIAL PLANTS AND ARTHROPODS: A COMPARISON OF THEIR STRUCTURE, COMPOSITION, AND WATERPROOFING FUNCTION
Authors: HADLEY N. F.
Published: January 2008

1. Lipids deposited on the surface or embedded within the cuticle of terrestrial plants and arthropods are primarily responsible for the observed low rates of water loss through the cuticle.

2. These lipids are a mixture of long‐chain compounds which include hydrocarbons (saturated, unsaturated, branched), wax esters, free fatty acids, alcohols, ketones, aldehydes, and cyclic compounds.

3. The cuticle of both plants and arthropods is a continuous, non‐cellular multilayered membrane which overlies the epidermal cells.

4. In arthropods, horizontal division of the cuticle into layers is clearly visible. In plants, the layers comprising the cuticle are not sharply demarcated.

5. The substance responsible for the structural integrity of the plant cuticle (cutin) is composed of cross‐esterified fatty acids; structural integrity in arthropod cuticle is provided by a chitin‐protein complex.

6. Cuticular lipids are probably formed near the surface in both plants and arthropods; however, specific sites of synthesis are known for only a few species and little is known about their transport from these sites to the surface. The elaborate pore canal and wax canal system of arthropod cuticle is absent from plants.

7. The physical structure and arrangement of the lipid deposits on the cuticular surface that are so important in controlling water movement depend on both quantity and chemical composition, and are, in turn, specific to each species in relation to its environment.

8. Different lipid components are not equally efficient in reducing transpiration. Maximum waterproofing effectiveness is provided by long‐chain, saturated, non‐polar molecules containing few methyl branches.

9. Plants and arthropods can, within genetic constraints, alter the composition of their cuticular waxes to improve impermeability when conditions require increased water conservation.

10. None of the models proposed to explain the change in arthropod cuticular permeability which occurs at a species‐specific temperature (‘transition temperature’) in many species is supported by the experimental data now available.
THE MOLECULAR AND CELLULAR BASIS OF PREIMPLANTATION MOUSE DEVELOPMENT
Authors: JOHNSON MARTIN H.
Published: January 2008

The formation of a mouse blastocyst involves the use of genetic information derived from the expression both of maternal genes in the preovulatory oocyte and of embryonic genes from the mid‐2‐cell stage onwards. Evidence is reviewed suggesting that maternal RNA transcripts made up to 20 days prior to ovulation are available for use after fertilization, that no significant KNA synthesis occurs between germinal vesicle breakdown and the mid‐2‐cell stage and that during this interval of transcriptional inactivity production of protein is regulated at a post‐transcriptional level. Embryonic genes first become active at the mid‐2‐cell stage and at, or shortly after, this time most maternal mRNA is inactivated. Thereafter, the available evidence suggests that although embryonic mRNA has considerable stability, much of it is translated immediately after it is transcribed. This tight linkage of mRNA transcription and utilization appears to be crucial for certain key events in development.

The cellular interactions operating during early development are described. It is suggested that asymmetry of cell contacts in the 8‐cell embryo imparts a mosaic structure to the embryo, and that this mosaicism is conserved and elaborated with division to the 16‐ and 32‐cell stages. The mechanisms are discussed by which mosaicism is induced and through which the two cell lineages of the blastocyst are founded.

Temporal events in preimplantation development show a periodicity of about 27 h. It is proposed that within each period differentiative events are cumulative but reversible, and that the boundaries between each developmental period constitute points of commitment at which reversal of development becomes no longer possible.
INSECT HORMONES IN DEVELOPMENT
Authors: RICHARDS G.
Published: January 2008

Advances in studies of prothoracicotropic hormone (ecdysiotropin), ecdysteroids and juvenile hormones in the past decade are considered:

1. Until recently there has been little progress with prothoracicotropic hormone. The development of a sensitive bioassay for the hormone promises to produce rapid advances.

2. Current methods of hormone analysis are described, with detection limits. The application of these methods in studies of hormones at different stages and in different tissues of insects have revealed a far greater complexity in hormone titres than was predicted from classical studies.

3. Very few studies employ chemical characterization of hormones and some assays do not distinguish biologically inactive metabolites of the hormones from the active hormones. Many studies have thus failed to reveal the numerous rapid fluctuations in hormone titre necessary for insect development.

4. While ecdysteroids act, via a receptor, on specific chromosome sites, the cellular mode of action of juvenile hormone in larval development is still unknown. Recent evidence suggests that juvenile hormone acts prior to the time at which its effects are realized by ecdysteroids.

5. Insect hormones produce dramatic changes in gene activity and their co‐ordinate control of specific protein synthesis has been the basis for a number of ‘model systems’ of gene control in higher eukaryotes.
PHOTOCONTROL OF STOMATAL MOVEMENTS
Authors: PEMADASA M. A.
Published: January 2008

1. Opening in light is a feature common to the majority of functional stomata, but the current argument is against the traditional view that light is the principal environmental promoter of opening, because stomata can open in the dark in response to CO2removal and/or temperature increase. In this review, evidence is provided that light is more efficient and effective than other physical factors in both producing and maintaining wide opening. However, light acts on stomata both directly and indirectly, in conjunction with changes in, for example, CO2balance, water regime and temperature of the leaf tissue.

2. Three general categories of light effects on stomata are recognized: (a) photosynthetic effects driven by metabolic processes, induced or enhanced by light, (b) hydrophotic effects mediating through light‐induced changes in epidermal turgor, and (c) photothermal effects arising from light‐dependent changes in leaf temperature.

3. Photosynthetic effects involve both CO2depletion, and starch mobilization, malate synthesis, H+extrusion, and accumulation of K+and C1‐in guard cells; these processes are triggered by light of different qualities: (a) Both blue and red light are involved in photosynthetic CO2fixation, utilizing energy from photosynthetic light reaction(s), which provides C precursors for synthesis of stornatal starch. (b) Blue light, but not red, enhances starch mobilization, PEP carboxylase activity and respiration. Accordingly, blue light is postulated to enhance hydrolysis of stornatal starch providing C3precursors for malate synthesisviaPEP‐fixation of endogenous CO2; the active extrusion of H+, derived from malate, is coupled with K+influx to guard cells. Malate and C1‐are competitive anions, for K+, and one begins to play a progressively more important role as the other becomes limiting; in intact leaves, however, malate plays a more decisive role. These processes are driven by the energy from blue‐light‐enhanced respiration. (c) Both photosynthetic fixation and PEP carboxylation act as CO2sensors, but the exact role of CO2in the stornatal mechanism has yet to be determined.

4. Hydrophotic and photothermal effects facilitate guard cell expansion by releasing epidermal pressure through enhanced evaporative water loss, and are, therefore, indirect effects of light; photothermal effects may also contribute to metabolic processes outlined in paragraph 3.

5. Stomatal closure in the dark accompanies starch synthesis, malate reduction, efflux of K+and C1‐from guard cells, and accumulation of CO2in substomatal cavities. Malate may be converted to starchviaC2compounds. Guard cells release K+and C1‐ into apoplastic space, from which they are removed by neighbouring cells. The entry of K+into neighbouring cells is supposed to be coupled with H+extrusion. These processes are dependent on respiratory energy.

6. The differential abaxial and adaxial stomatal light responses are related to inherent metabolic differences between the two epidermes, but the biochemical basis is not known.
ARTHROPODS THAT PREY ON VERTEBRATES
Authors: McCORMICK SHARON , POLIS GARY A.
Published: January 2008

1. Many arthropods are predators of vertebrates: four orders of the class arachnida, six orders of insecta, five orders of crustacea and one order of chilopoda include species that have been reported to eat vertebrates. At the population level, some arthropods are responsible for significant mortality among some vertebrates.

2. Arthropods are well equipped for this type of predation; many are larger than vertebrates (approximately 20% of the vertebrate fauna of eastern North America is less than 10 cm in length), they may hunt in social groups and many have toxins or other adaptations that increase predatory efficiency.

3. Several arthropod predators and vertebrates may be involved in cross predation, the species eating each other. The switch in the role of predator and prey occurs during ‘ontogenetic reversal’ as the vertebrate grows from small and vulnerable to large and predaceous. Cross predation decreases the future risk for one's self or offspring.

4. The opportunity for arthropod predation on vertebrates exists in many communities, but a review of some food webs catalogued by Cohen (1978) indicates that this particular link may be easily overlooked. Some arthropods should be investigated as potential predators of vertebrates.

5. The information available from the analysis of feeding interactions in a community should be an important link between field and theoretical ecology; however, most food webs are probably underestimates of the complexity that is commonplace.
SELENIUM: TOXICITY AND TOLERANCE IN HIGHER PLANTS
Authors: Brown T. A. , Shrift A.
Published: January 2008

1. Different plant species show considerable variation in their selenium content. Primary indicators, also termed selenium accumulators, many of which are members of the genus Astragalus, are highly tolerant of selenium; they are known to contain tissue levels of several thousand µg selenium/g. Secondary indicators, tolerant to low concentrations of the element, may absorb up to 1000 µg selenium/g. Non‐accumulators are poisoned by selenium.

2. The toxicity of selenate (SeO4‐) and selenite (SeO3‐) to most plants can be attributed to a combination of three factors. Firstly, selenate and selenite are readily absorbed from the soil by roots and translocated to other parts of the plant. Secondly, metabolic reactions convert these anions into organic forms of selenium. Thirdly, the organic selenium metabolites, which act as analogues of essential sulphur compounds, interfere with cellular biochemical reactions.

3. Incorporation into proteins of the amino acid analogues selenocysteine and selenomethionine, in place of the equivalent sulphur amino acids, is considered to be the underlying cause of selenium toxicity. The physical and chemical differences between selenium and sulphur will result in small, but significant, changes in the biological properties of a selenium‐substituted protein.

4. Selenium‐tolerant accumulator plants differ in at least two respects from sensitive species. Large quantities of Se‐methylselenocysteine and selenocystathionine, two non‐protein selenoamino acids rarely detected in non‐accumulators, have been isolated from the tissues of selenium accumulators. In addition, selenium is kept from entering proteins so that the selenium levels in proteins of accumulator plants is significantly lower than the levels in selenium‐sensitive plants.

5. Exclusion of selenium from the proteins of accumulators is thought to be the basis of selenium tolerance. Discrimination against selenocysteine during protein synthesis seems to prevent incorporation of this selenoamino acid into proteins of accumulators. Furthermore, synthesis of Se‐methylselenocysteine and selenocystathionine, which results in diversion of selenium away from the synthesis of selenomethionine, will restrict the amount of this compound available for protein synthesis.

6. Selenium accumulation among unrelated plant genera is a striking example of convergent evolution. The possibility that accumulation of this element is associated with a nutritional requirement for selenium, although explored in the past, is still in need of further clarification.
CHEMO‐ORIENTATION
Authors: BELL WILLAM J. , TOBIN THOMAS R.
Published: January 2008

1. A new classification system for chemo‐orientation mechanisms is suggested, based on delineating (a) internal and external orientation information available to an organism, (b) mode of information processing, (c) type of motor output pattern, and (d) guidance systems that modulate or direct motor output.

2. Cross‐phyletic comparison of chemo‐orientation indicates that morphology, to a greater extent than phylogeny, determines the kind of chemo‐orientation mechanisms available to an organism. Analogies are drawn between single‐celled organisms with surface chemical receptor sites and higher organisms with elaborate chemosensory organs and nervous systems.
ENVIRONMENTAL EFFECTS ON ANIMALS USED IN BIOMEDICAL RESEARCH
Authors: CLOUGH G.
Published: January 2008

I. Reliability of the results of bio‐medical research clearly depends upon the animals used showing as standard responses as is possible.

2. The majority of animals used in this field are small, homoiothermic mammals which have sensitive and strong homeostatic mechanisms. If a change in ambient conditions is of sufficient magnitude to unbalance homeostasis, then the neuroendocrine system is stimulated so as to restore it, and this can interfere with the response to test conditions or agents.

3. The homeostatic effectors involved are diverse and can include both physiological and behavioural changes in the animal. These can affect metabolic rate, body temperature, activity, food consumption, hormone concentration, wake/sleep patterns, maturation, posture, lactation and many other bodily functions. Any of these changes is potentially capable of influencing experimental results.

4. The evidence presented shows how environmental factors may affect the outcome of experiments in the fields of animal behaviour, cancer research, immunology, pathology, pharmacology, psychology, reproduction, teratology and toxicology; particular attention is paid to the effects of ambient temperature, relative humidity, air movement and quality, light and sound.

5. While a constant, reproducible environment would be ideal, there is little possibility of controlling all the variables; nevertheless all investigators should minimize those environmental variables that have been shown to be important.

6. To enable other investigators to repeat experiments or carry out comparative studies, environmental conditions pertaining during an experiment should be adequately described in any publications.
THE MECHANISM OF α‐ADRENERGIC AGONIST ACTION IN LIVER
Authors: REINHART PETER H. , TAYLOR WAYNE M. , BYGRAVE FYFE L.
Published: January 2008

1. Although the mechanism of action of a‐adrenergic agonists in liver tissue is somewhat complex, a number of experimental approaches can be usefully employed to identify the molecular details of the events that occur.

2. Receptors specific for α1‐adrenergic agonists located on the plasma membranes of rat liver cells have been partially characterized using pharmacological agents, affinity labels and monoclonal antibodies. Much of this work has employed isolated plasma membrane fractions and does not take account of tissue‐related factors which may now be studied in the intact perfused rat liver, following the development of an appropriate assay system.

3. Because a redistribution of cellular Ca2+ is central to the mechanism of action of a‐adrenergic agonists in liver, it is important to first gain an understanding of basic cellular Ca2+ regulation. Knowledge about the compartmentation of cellular calcium and about Ca2+‐translocation systems located in the mitochondria, plasma membrane and endoplasmic reticulum is now quite extensive. However, the role of mitochondria in the regulation of intracellular Ca2+ is still unclear; it now appears that the mitochondrial calcium content is much less than considered previously. This may have important implications for such a regulatory role.

4. The sequence of Ca2+ movements that may occur when a‐adrenergic agonists interact with liver have been identified and are as follows: (a) Ca2+ is mobilized from an intracellular pool(s) (mitochondria plus endoplasmic reticulum and/or plasma membranes). (b) This elevates the cytoplasmic free Ca2+ concentration and leads to an efflux of the ion from the cell. (c) At this time, Ca2+‐sensitive metabolic events in the cytoplasm are activated and an increase in Ca2+‐cycling occurs across the plasma membrane. (d) Immediately after the hormone is withdrawn, there is a net influx of Ca2+ into the cell, and the intracellular Ca2+ pools and transmembrane fluxes are restored to the pre‐induced states. In this model, Ca2+ movements across the plasma membrane play a key role in regulating the cytoplasmic Ca2+ concentration.

5. In the perfused rat liver it has been possible to define in quite precise terms the amounts and rates of Ca2+ mobilized in each of these stages.

6. Although several proposals for ‘second messengers’ to link the hormone‐receptor interaction with initial Ca2+ mobilization have been made, at this time only polyphosphoinositide turnover appears to be a suitable candidate.
CUTANEOUS GAS EXCHANGE IN VERTEBRATES: DESIGN, PATTERNS, CONTROL AND IMPLICATIONS
Authors: FEDER MARTIN E. , BURGGREN WARREN W.
Published: January 2008

1. The exchange of oxygen and carbon dioxide between skin and environment is commonplace in the vertebrates. In many lower vertebrates, the skin is the major or even sole avenue for respiration.

2. As implied by the physical laws governing diffusion of gases, the skin diffusion coefficient, surface area, gas diffusion distance and transcutaneous gas partial pressures may independently or jointly affect cutaneous respiration. In vertebrates, each of these variables has undergone modification that may be related to dependence upon cutaneous gas exchange.

3. Both theoretical models and experimental data suggest that cutaneous gas exchange is limited by the rate of diffusion. However, changes in convection of the respiratory medium and of blood may partially compensate for diffusion limitation, and potentially function in the regulation of cutaneous gas exchange.

4. Typically, the skin is one of several gas exchangers, although many salamanders and some species in other vertebrate groups breathe solely through the skin. The cutaneous contribution to overall gas exchange is often most important in small animals, at cool temperatures, at low levels of activity and in normoxic and normocapnic conditions. Branchial and pulmonary respiration increasingly predominate in other circumstances.

5. Often, the skin figures more prominently in CO2, excretion than in O2, uptake.

6. Cutaneous gas exchange emerges in vertebrates as a process perhaps less effective and more constrained than branchial or pulmonary exchange but also less energetically costly. Its utility is indicated by its wide and successful exploitation in vertebrates occupying a diverse array of habitats.
ISLAND BIOGEOGRAPHY AND PALAEOBIOLOGY: IN SEARCH FOR EVOLUTIONARY EQUILIBRIA
Authors: HOFFMAN ANTONI
Published: January 2008

1. The concept of evolutionary equilibrium has been derived from the theory of island biogeography via an ecological rationale for increase in species extinction rate and decrease in speciation rate with increasing diversity of the system.

2. This concept is theoretically plausible at the species level and at a regional scale but, in spite of several empirical tests in the fossil record, it has thus far remained unsupported by empirical evidence. In order to test it conclusively, one has to analyze not only the pattern of species number through time but also its relationship to speciation and species extinction rates; independent evidence for perturbations must also be available.

3. The concept of evolutionary equilibrium at the global scale must be extrapolated over higher levels of taxonomic hierarchy, for reliable species‐level data are unavailable at this scale. A theoretical justification for this concept cannot, then, be derived from the theory of island biogeography.

4. The rates of family extinction and origination in the Phanerozoic show no evidence for diversity‐dependence, which undermines most quantitative models of biotic diversification based on the concept of global evolutionary equilibrium. Rigorous testing of these models cannot be done at the present state of knowledge because of the uncertainty about the empirical pattern (sampling and taxonomic biases, absolute time scale).
THE EVOLUTION AND COMPARATIVE PHYSIOLOGY OF TERRESTRIAL AND FRESHWATER NEMERTEANS
Authors: MOORE JANET , GIBSON RAY
Published: January 2008

(1) Parallel evolution from separate marine ancestors has given rise to two groups of genera of terrestrial nemerteans, representative of at least two different family stocks. They have colonized land by the direct route, moving up the shore on widely separated oceanic islands. The relationships between the known terrestrial and semi‐terrestrial nemerteans, comprising seven genera and 15 species, are defined and their geographic distribution is discussed.

(2) In fresh water, three heteronemertean and nine hoplonemertean species are known. The hoplonemerteans arise from two different families representing two different evolutionary routes to fresh water, one by way of estuaries and the other via land. The distribution of freshwater nemerteans and the characters common to all species are discussed.

(3) Very little is known about the comparative physiology of land and freshwater nemerteans. However, information about the physiology of marine forms is combined with morphological differences from them found in terrestrial and freshwater species to suggest profitable lines of future research.

(4) Water relations pose a major problem for both terrestrial and freshwater nemerteans. The role of the cerebral organs, the blood and the excretory system in the osmotic physiology of some littoral nemerteans is beginning to be understood. These systems in land and freshwater forms have clearly distinctive features which need to be thoroughly investigated.

(5) Suggestions are given for valuable lines of investigation of the mucous glands, digestive physiology and general behaviour of terrestrial and freshwater nemerteans.
THE BIOLOGY OF PUBERTY
Authors: BRONSON F. H. , RISSMAN EMILIE F.
Published: January 2008

The objective of this review was to develop a broader, more biological, overview of puberty, as opposed to the more limited, laboratory‐dominated, view that has emanated from experimental physiology. Three conceptual schemes form the basis for our broader perspective. The first deals with the ways in which genes and environmental factors interact to program the timing of reproductive development. The second focuses on the ways environmental factors interact with each other to influence puberty. The third relates the genetic and environmental controls to specific endocrine and neuroendocrine pathways of action.

The more traditional approach of studying domesticated animals under carefully controlled conditions predetermines one's conclusions. One logically will conclude that the final stages of reproductive development are rather rigidly determined genetically and not greatly subject to environmental regulation, except for obviously adaptive pheromonal and photoperiodic regulation. One also will search within the reproductive axis itself for the final developmental step that allows functional fertility. In contrast, a more biological view suggests that for most mammals puberty is a highly labile process subject to several kinds of environmental influences that operate at many times during a mammal's life. Furthermore this perspective suggests that the final developmental step allowing fertility onset normally will occur outside rather than within the reproductive axis proper. This conclusion has a potentially great impact upon the way we look at the organization of the brain and endocrine system and in the way we choose animal models for studying human puberty and the types of controls we study.
NUTRIENT TRANSPORT BY THE CRUSTACEAN GASTROINTESTINAL TRACT: RECENT ADVANCES WITH VESICLE TECHNIQUES
Authors: AHEARN GREGORY A.
Published: January 2008

1. Techniques are described for producing purified brush‐border membrane vesicles (BBMV) of crustacean hepatopancreas which can be used to examine the characteristics of solute transport at the apical pole of hepatopancreatic epithelial cells.

2. Hepatopancreatic BBMV illustrated Na‐dependent, carrier‐mediated sugar transport which was electrogenic and sensitive to pH. Increased proton concentration lowered the Michaelis‐Menten constant for glucose transport and increased the apparent diffusional permeability of the membrane to sugar.

3. Transports of L‐alanine and L‐lysine by hepatopancreatic BBMV were Na‐independent, carrier‐mediated, and strongly sensitive to transmembrane electrical potential after protonation at acidic pH. L‐alanine and L‐lysine were competitive inhibitors of each other for influx into BBMV and also illustrated trans‐stimulation, suggesting that both amino acids use the same transfer mechanism. L‐Leucine was a non‐competitive inhibitor of L‐lysine influx and may employ a distinct Na‐independent transport process.

4. L‐glutamate transport after protonation at acidic pH was Na‐dependent, suggesting that a different transport mechanism was responsible for its movement across hepatopancreatic BBMV than that facilitating the transfer of alanine or lysine.

5. Preliminary experiments indicate the presence of Na/H antiport in hepatopancreatic BBMV, providing, for the first time, a possible mechanism for gastrointestinal luminal acidification in crustaceans.

6. A proposed model for nutrient transport by crustacean hepatopancreatic BBMV is presented which suggests that transapical transfers of both sugars and amino acids are strongly influenced by in vivo luminal acidification. Luminal protons have at least two major effects on nutrient transport in these animals: (a) titration of sugar transport proteins with subsequent stimulatory effects on influx kinetic constants; (b) protonation of luminal amino‐acid‐charged moieties and conversion into appropriate substrates for transport by either Na‐dependent or Na‐independent, membrane‐potential‐sensitive carrier proteins.
SPERM THRUSTS AND THE PROBLEM OF PENETRATION
Authors: GREEN D. P. L.
Published: January 2008

An equation of Lighthill's is used to calculate sperm thrusts. They have values in the range 5–350 pN, depending on species. The limitations of this approach are discussed and comparison is made with the measured thrust for human sperm. The effect of sperm thrusts of this magnitude on covalent bonds and reversible bonds is discussed. Sperm cannot break covalent bonds, but can reduce the lifetime of reversible bonds.

The structure and physical properties of the zona pellucida are examined in relation to sperm penetration. The evidence suggests that sperm cannot penetrate it solely by force. A model for sperm penetration is elaborated in which the conjunctive application of thrust and a soluble enzyme leads to strain‐induced proteolysis and the formation of the penetration slit. The potential mechanism of the zona block is discussed, as is the site of the acrosome reaction. The effects of other mechanical inputs into fertilization such as stirring and swimming are examined briefly. Evidence suggests that sperm penetration of the cumulus oophorus and cervical mucus is mechanical, but that in the case of cervical mucus, it is affected by changes in the physical properties of the mucus.
THE ROLE OF METABOLISM AND CALCIUM IN THE CONTROL OF MITOSIS AND OOPLASMIC MOVEMENTS IN INSECT EGGS: A WORKING HYPOTHESIS
Authors: MEER JITSE. M. VAN DER
Published: January 2008

Patterns of mitosis and ooplasmic movements in the plasmodial phase of insect embryogenesis and their supramolecular basis are reviewed. Evidence is provided for both the relative independence and the precise correlation of the nuclear cycle and various cycling movements of the ooplasm. I suggest that the timing of these cycles is controlled by a metabolic cycle. The latter may act via a cyclic rise and fall either of the level of free calcium or of the sensitivity of contractile cytoplasmic proteins to a constant level of free calcium. Thus mitotic patterns may reflect metabolic patterns, which in turn may reflect the distribution and activity of mitochondria and may also be related to egg size and shape by a gradient of surface‐to‐volume ratios. The total number of cycles may depend on a limiting cytoplasmic factor, which together with the number of nuclei in a given cycle defines the nucleo‐cytoplasmic ratio. I also propose that both natural and experimental activation of insect eggs trigger the metabolic cycle either directly, by supplying oxygen or water, or indirectly, via a calcium pulse. Possible molecular mechanisms of control are discussed and applied to mitosis and ooplasmic movements. A brief discussion of various cell cycle models in light of data from insect embryogenesis is included.
HISTORY OF ARIDLAND VEGETATION AND CLIMATE: A GLOBAL PERSPECTIVE
Authors: SINGH GURDIP
Published: January 2008

1. The origin and history of aridlands and their vegetational cover is closely related to geological history, especially in relation to plate tectonics, mountain building, land‐and sea‐level changes and ice ages, and the arrival of modern humans and their subsequent development.

2. A close relationship exists between world temperatures and precipitation. Therefore, the development of present‐day zonal, aridland vegetation and climate cannot be divorced from the history of the latest ice age.

3. The combined geological and palaeobotanical evidence demonstrate that whilst the origin of modern openland and aridland vegetation went back to the time of the origin of angiosperms during the Cretaceous, its subsequent expansion went hand in hand with the lowering of world temperatures during the Palaeogene and Neogene, when a series of angiospermous families having dominantly herbaceous and openland taxa, as members, appeared successively in the stratigraphic record.

4. The successive lowering of world temperatures had the overall effect of reducing precipitation levels all over the globe. Consequently, high rainfall areas, bearing closed forests, became progressively smaller and smaller and the decreased rainfall promoted the evolution and expansion of low biomass, openland and aridland vegetation.

5. The break‐up of regional closed forests had started from the middle Miocene but the main expansion of zonal, aridland vegetation, in low and middle latitudes, appears to have taken place, together with the expansion of tundra vegetation, at high latitudes, from the late Pliocene. Glaciations of a magnitude of at least two‐thirds that of the late Pleistocene glacial maxima started to occur about that time, 25 Ma ago.

6. The alternations between cold, glacial and warm, interglacial periods, during the late Neogene, especially with increased amplitude during the last 0.4 Ma, allowed less and less time for forest vegetation to expand and stabilize during the warm intervals, with the result that openland and aridland vegetation was able to expand to unprecedented levels.

7. Further, as man increased fire frequencies during the late Pleistocene, the relatively fire‐sensitive and mesophytic taxa were selectively eliminated and more and more forests were opened to invasion by openland taxa in low and middle latitudes. Later on, with the clearance of forests for agriculture, the overall effect on vegetation was to create open landscapes which favoured the expansion of openland taxa at low, middle and high latitudes, during an interglacial, that is, the Holocene, a feature that is unprecedented in the entire earlier geological record.