bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE EVOLUTION OF SEX IN FLOWERING PLANTS
Authors: LEWIS D. 
Published: January 2008

Summary1. The importance of combined genetic and systematic analysis of sex for its evolutionary interpretation has long been understood in animals. It now seems possible to make ah evolutionary interpretation of sex in plants by similar methods.2. From the sporadic distribution of dioecious species throughout mainly hermaphrodite families of flowering plants, it is inferred that dioecious species have evolved from hermaphrodites.3. From the more frequent association of dioecious species with monoecious species than with hermaphrodites, it is inferred that they have evolved more frequently by means of a monoecious intermediary.4. Highly organized sex‐determining mechanisms of dioecious plants can evolve from single gene segregation, as shown (a) by the synthesis of dioecious strains of hermaphrodite species, and (b) by the analysis of sex in dioecious species of plants.5. This evolution is illustrated by the study of sex chromosomes and shows the transition from the type where the two chromosomes are indistinguishable to highly complex systems. Lower stages are commonest in plants, higher stages in insects and mammals.6. Male sterility which has become established in wild populations of hermaphrodite species is cytoplasmically inherited in all known cases. This system is not considered to be a transitional stage in the development of dioecy but rather as another stable outbreeding mechanism.7. Sporadic distribution and lower differentiation of sex chromosomes agree in showing that sex differentiation is short‐lived in flowering plants. This is to be expected since sex separation in sessile organisms, in comparison with other outbreeding systems in plants, suffers from two shortcomings: (a) that the degree of outbreeding is inflexible, and (b) that utilization of gametes is wasteful. Male sterility is not subject to these limitations.8. This gametic wastage is mitigated by changes in the sex ratio. Such changes are effected by the differential pollen tube growth of male and female determining pollen grains. For this reason it is the male that usually becomes the heterogametic sex.9. We can thus have an intelligible evolutionary interpretation of sex in plants when we consider (a) the sporadic occurrence of sex separation, (b) the simplicity of the mechanism determining this separation, and (c) the great diversity of other sexual breeding systems.
EXTEROCEPTIVE FACTORS IN SEXUAL PERIODICITY
Authors: A. MARSHALL F. H. 
Published: January 2008

Summary1. In all mammals and probably in all vertebrates there is an internal endocrine sexual rhythm with alternating periods of rest and activity. This cycle is usually adjusted to external seasonal changes and with some marked exceptions spring is the period of greatest sexual activity, but there is much specific variation and among ruminating mammals breeding is generally in autumn.2. Among tropical and subtropical animals breeding is not nearly so restricted to definite seasons, and there is evidence that ecological factors play a part in its recurrence.3. In individual animals which are made to cross the equator there may be two seasons of sexual activity in the year and the times of breeding are eventually reversed though the original endocrine rhythm may be partly maintained for some time.4. Experiments with light and ultra‐violet irradiations indicate that with the majority of vertebrates exteroceptive stimuli dependent upon these processes are of primary importance in adjusting the cycle to changing periodic environmental conditions.5. The evidence shows that the factors in question act through the intermediation of the central nervous system and the anterior pituitary body.6. The cycle is liable to considerable modification by exteroceptive stimuli arising from the relations between the sexes and between the mother and her offspring. Thus ovulation in various species of vertebrates may depend upon stimuli normally arising from the male but which may be imitated by experimental methods.7. Sexual display and courtship phenomena among various classes of animals, while undoubtedly in some species serving to keep the pairs together and thus securing a ‘marriage bond’, have the further and much more general function of promoting an effective synchronization of the male and female sexual processes, thus favouring successful procreation.8. The synchronization is mainly effected by pituitary stimulation which is often mutual, the stimuli acting through the intermediation of the hypothalamus, as in the case of other stimuli.9. Whatever the exteroceptive stimulus the anterior pituitary is the regulator of the gonadal function.
BIOLOGICAL RACES IN PARASITIC PROTOZOA
Authors: HOARE CECIL A. 
Published: January 2008

SummaryBiological races are defined as such subdivisions of a morphological species as are distinguishable by differences in biological characters only. Though biological races are well represented in diverse groups of parasitic Protozoa, their true nature is in most cases concealed under separate specific names.In parasitic Protozoa biological races differ from each other in various aspects of their host‐parasite relations. These may be manifested in host‐restriction (or host‐specificity), as in trypanosomes of the brucei group, containing races confined to man and to other mammals; in intestinal amoebae and flagellates comprising human and batrachian races; and in human and simian malaria parasites (Plasmodium). Likewise, races parasitic in the same vertebrate host may be restricted to distinct vectors, as in piroplasms (Babesia) of cattle and dogs.There are races which cause different diseases in the same host, usually with a distinct localization in its tissues, e.g. Leishmania in man and dogs, and trypanosomes of the evansi group, causing dourine and surra. Others again vary in the degree of virulence to the host, e.g. piroplasms of the genera Theileria and Babesia. A variation in pathogenicity to one or more hosts characterizes some geographical races of the same parasite, e.g. local strains of human Plasmodium, and of Trypanosoma evansi. Finally, in certain races various differential characters may be combined.Variations in the host‐parasite relationship, as manifested by different races of Protozoa, are determined by the degree of their adaptation to the physical and chemical conditions in the host. These conditions include, among others, body temperature, quality of the digestive juices, nutrition (diet), and properties of the serum (parasiticidal action). The mutual adaptation of parasite and host involves reciprocal reactions, among which the serological reactions of the host are especially interesting, for they throw light on the intimate constitution of parasitic microorganisms. There is reason to believe that biological races of some parasitic Protozoa‐like the intraepecific ‘types’ of bacteria‐differ from each other in antigenic composition, while retaining common antigens characteristic of the species as a whole. Antigenic constitution is, therefore, correlated with the biological peculiarities of these races (at least in blood parasites), and since antigens consist of qualitatively different chemical substances, the distinction between biological races resolves itself into differences in the chemical structure of the antigenic components of the organisms in question. Biological races in parasitic Protozoa appear to be stable and hereditarily fixed. The biological criteria for their differentiation and the constancy of their diagnostic characters are advanced as arguments in support of an independent taxonomic status for biological races.
INTERRELATIONSHIPS AND TAXONOMY OF THE DIGENETIC TREMATODES
Authors: STUNKARD HORACE W. 
Published: January 2008

SummaryThe 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

SummaryThe 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

SUMMARYInformation 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

SUMMARYOn 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

Summary1. 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.
THE PHYLOGENY OF THE SALIENTIA
Authors: GRIFFITHS I. 
Published: January 2008

Summary1. The essentially recent skeletal patterns of fossil Salientia indicates that the evolutionary relationships of the order must continue to be assessed on evidence obtained chiefly from a study of recent forms.2. The morphology and morphogenesis of the more important criteria employed in taxonomic analyses are described. Definitive and developmental features of pectoral and vertebral elements are particularly detailed. It is concluded that: (a) neither the nature of the vertebral articulation nor the arrangement of the thigh complex is a reliable character on which to define major salientian categories; and (b) criteria based on degree of freedom of epicoracoid cartilages are incapable of exact taxonomic application. The Arcifera and Firmisternia are redefined according to the presence or absence of epicoracoid horns. The importance of certain morphogenetic patterns in the analysis of phylogenetic trends is suggested.3. A new scheme is proposed for the definition of recent salientian families. This hinges chiefly on the number of presacral vertebrae, the nature of the definitive centrum and the epicoraco‐sternal complex.4. The status of Protobatrachus (L. Trias) is reviewed. It is concluded that the proanuran stock stemmed from temnospondylid ancestors and that the so‐called ‘saltatory’ trends of modern Salientia evolved primarily for swimming. Fossil footprints from the Ecce formation of South Africa may indicate that the Proanura were already established by the Permian. The role of the urostyle in facilitating the pro‐anuran‐salinetian transition is considered.5. On the evidence of the vertebral column it is suggested that the Salientia are at least diphyletic and that all non‐ascaphid forms stemmed from a pipoid stock. Interrelationships between the non‐ascaphid families are considered.6. The geographic history of the order is reviewed. It is concluded that early salientian evolution was rapid and radiative and that, skeletally at least, the essential features of all the recent families had been established by the Tertiary or, possibly, by the Mesozoic. Discoglossidae, Pipidae and Pelobatidae are interpreted as eco‐1 ogically isolated and the Atelopodidae as Neotropical in both origin and range. Whilst the main ranoid and bufonid stocks almost certainly originated in and radiated from the Old World tropics (as Darlington suggested) some of their derived lines (Rhaco‐phoridae and Microhylidae in particular) may equally well have evolved polycentrically without much subsequent radiation.7. It is suggested that radiation or isolation, in the different families, is a function of locomotory specializations and that these are reflected particularly in the variations of the vertebral centrum and the shoulder girdle.I wish to thank Miss A. G. C. Grandison, Professor Georg Haas, Professor J. P. Lehman, Dr H. W. Parker, the late Dr Malcolm Smith and Dr L. C. Stuart who have assisted me either with helpful discussions and information or with gifts of material. I am also indebted to Dr A. W. Crompton for photographs of the fossil footprints from the Ecce formation.