摘要:

Allgemeine Zusammenfassung.1. Die Herkunft des Regenerationsmaterials wurde bisher bei den Poriferen, Coelenteraten, Turbellarien, Nemertinen, Polychäten, Oligochäten, Sipunculoiden, Bryozoen und Tunikaten, sowie in einzelnen Fällen auch bei Arthropoden, Mollusken und Echinodermen verfolgt.2. Die Wundheilung geschieht in den meisten Fällen durch Überdeckung der Wunde mit der Epidermis, deren Zellen aktiv darüber hinwegwandern, manchmal unterstützt durch von unten einwandernde mesenchymale Zellen.3. Unter den drei Keimblättern ist das Entoderm das selbständigste. Der Darm wird fast immer vom Stumpf aus regeneriert, wahrscheinlich unter Benutzung der Basalzellen. Wo kein Stumpf vorhanden ist, kann seine Bildung manchmal vom Mesenchym aus erfolgen.4. Das Ektoderm ist bei der Regeneration auf die Unterstützung durch totipotente Zellen angewiesen, unter deren Wirkung vielfach eine Embryonalisierung der Epidermis erfolgt. Das Ektoderm ist also die am weitesten differenzierte Körperschicht.5. Das Mesoderm (s. 1.) ist das am wenigsten differenzierte Keimblatt und liefert in vielen Fällen totipotente oder dedifferenzierte Zellen, die zuweilen alle Organe wiederherstellen können.6. Die totipotenten Zellen treten entweder in der Form der Neoblasten oder als Basalzellen, vielleicht auch als Peritonealzellen auf. Alle diese Formen von Regenerationszellen können als Blastocyten (Stolte) zusammengefasst werden.7. Die Schwämme besitzen zahlreiche Zellformen, die, künstlich getrennt, nach teilweiser Dedifferenzierung die Organe wieder aufbauen. Die totipotenten Zellen sind hier die Archäocyten.8. Wo ein Mesoderm fehlt, wie bei den Coelenteraten, liegen die sog. interstitiellen Zellen im Ektoderm, können aber auch in das Entoderm überwandern.9. Für die Tunikaten ist noch nicht entschieden, ob die Regenerate von mesenchymalen Zellen, speziell von den sog. Tropfenzellen (Spek) aufgebaut werden.10. Bei den höher differenzierten Tiergruppen der Arthropoden, Mollusken und Echinodermen ist über die Herkunft des regenerativen Zellmaterials bisher nur wenig bekannt geworden. Die gute Regenerationsfähigkeit der Asteroiden, Ophiuriden und Holothurien unter den Echinodermen lässt vermuten, dass in diesen Organismen überall Zellreserven zur Verfügung stehen.Summary.1. The origin of regenerative material has been studied in sponges, coelenterates, turbellarians, nemerteans, polychaetes, oligochaetes, sipunculids, polyzoa and tunicates, and in a few instances also in arthropods, molluscs and echinoderms.2. In most cases the healing of a wound is accomplished by the active migration of epidermal cells, often aided by mesenchyme cells moving up from beneath.3. Of the three germ layers, the endoderm is the most independent. The gut is almost always regenerated from its stump, probably with the help of basal cells. When there is no stump, the formation of the gut may be sometimes accomplished by mesenchyme.4. The ectoderm, which is the most differentiated germ layer, is assisted in regeneration by totipotent cells, which to a great extent render the epidermis embryonic.5. The mesoderm is the least differentiated germ layer and in many cases it furnishes totipotent, or dedifferentiated, cells which in certain cases can regenerate all organs.6. The totipotent cells take the form either of neoblasts or of basal cells, and perhaps also of peritoneal cells. All these types of regenerative cells may be called blastocyts.7. Sponges possess many sorts of cells, which, when artificially separated from one another, can reconstitute the organs, after they have undergone partial dedifferentiation. In this case the archaeocytes are the totipotent cells.8. When there is no mesoderm, as in the coelenterates, the so‐called interstitial cells lie in the ectoderm, but can also migrate into the endoderm.9. In tunicates it has not yet been decided whether or not regeneration is accomplished by mesenchyme cells, and particularly by the so‐called “drop‐cells”.10. Little is known concerning the cellular basis of regeneration in the more highly differentiated groups of a

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00495.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00496.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

Summary.The high urea content (2·0 and 2·5 per cent.) that characterises the blood, body fluids and tissues of the Elasmobranchii owes its origin to the relative impermeability of the gills and integument to this substance, and to the circumstance that the urea is actively conserved by the elasmobranch kidney.In consequence of this physiological uraemia, the elasmobranch is osmotically superior to its environment, even in sea water, and is able to absorb at least a minimum quantity of water for the formation of a urine that is isotonic or hypotonic to the blood, in accordance with the osmotic limitations of the fish kidney.We may suppose that the uraemic state tends to develop and to be regulated more or less automatically; urea is constantly being formed by the ordinary metabolic combustion of protein; water shortage leads to oliguria and urea retention, and the accumulated urea in the blood raises the osmotic pressure of the latter to a point where water is again available by direct absorption. Water plethora (as in fresh water) leads to diuresis and increased urea excretion, which in turn lowers the osmotic pressure of the blood and in some measure, at least, reduces the rate of water absorption.Trimethylamine oxide, which imparts about one‐quarter as much osmotic pressure to the blood as does urea, is also conserved by the elasmobranch; the fact that this substance is present in the urine in lower concentration than in the blood suggests that, like urea, it is actively reabsorbed from the glomerular filtrate.This physiological uraemia is apparently an archaic biochemical habit acquired early in elasmobranch evolution, since it is shared by the divergent orders of the subclass. Presumably it is a secondary mode of osmotic regulation superimposed upon the more primitive one of branchial regulation, as observed in the teleostomes.The cleidoic egg, unique (among the fishes) in the Elasmobranchii, and the viviparous mode of reproduction, are viewed as adaptations to urea retention, protecting the embryo against the loss of urea during its early development.Urea retention enables the Elasmobranchii to maintain a considerably greater rate of urine formation (water excretion) than is observed in the marine teleosts, a fact that perhaps explains why the former do not show the glomerular degeneration or the aglomerular development observed in the latter.Whereas urine formation in the marine teleosts appears to be carried on normally at a reduced level considerably below the maximum possible rate, the elasmobranchs appear to maintain a maximal (though small) degree of glomerular activity at all times. Unlike the teleosts, they appear to possess no mechanisms for reducing glomerular activity; it may be that because of their superior osmotic position, due in turn to their physiological uraemia, they have never been faced with the necessity for conserving water to an excessive degree in the kidneys, and have therefore never evolved the means for doing

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00497.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

Summary.1. Previous work on the behaviour of genes in interspecific crosses is discussed, and it is concluded that allelomorphic relationships exist between the genes of crossable species whether these are in the same genus or in reputedly different genera2. Genetical experiments on interspecific hybrids in six species of the genusGossypiumenable the following main conclusions to be drawn:(a) Although allelomorphic relationships exist throughout the six species in respect of all genes examined, cases of identity (apparent or real) are practically confined to recessive genes only. Geographical isolation over a long period of time has resulted in the production of new alleles at most loci. These may be termed “species alleles”. Species endemic in the Galapagos and Hawaiian Islands are characterised by species alleles not found in mainland species.(b) The introduction of genes from one species into another indicates that species differ not only in the mode of distribution of alleles functioning as main genes, but also in the modifier complexes accompanying such alleles. The degree to which modifier complexes differ in species is of primary importance from a taxonomic point of view.(c) The bearing of experiments with the “Crinkled” mutant on the Fisher theory of dominance is discussed. It is shown that a number of normal alleles of crinkled exist, which are distinguishable only by their dominance potency, that the dominance relation is due to the interaction of a normal allele of specific potency with a modifier complex to which it is precisely adjusted, and that the genes constituting the dominance modifier complex have been preserved not because of their function as modifiers of initially disadvantageous heterozygotes, but because of their selective value on their own account. It is believed, however, that on the appearance of the crinkled mutant, selection probably ensued in favour of alleles with greater dominance potency,i.e.that the “Haldane effect” has been operative.(d) Examples are given of three different ways in which homologous characters can be genetically constructed in the genusGossypium.It is pointed out that the conception of continuous change with time in the genetical architecture of an organ is probably of profound evolutionary significance.3. The Darwinian process of evolution by natural selection, involving mere gene substitution, has probably been the main mechanism involved in the profound changes induced in the genusGossypiumthrough geographica

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00498.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

Summary.1. The vertebrate labyrinth can be divided into a pars superior, consisting of the utriculus and the semicircular canals, and a pars inferior, consisting of the sacculus and its various appendages.2. Only the pars superior is concerned with the maintenance of muscle tone and with reflex reactions to gravity and to linear and angular accelerations. This has been demonstrated for fishes, amphibia and mammals, and, although the evidence is not completely satisfactory, it probably holds for reptiles and birds as well.The pars inferior takes no part in any of these functions (again with the above reservation as to reptiles and birds), but, even in those vertebrates which lack the organ of Corti, is concerned with sound reception.Breuer's theory of the localisation of the non‐acoustic function of the labyrinth has thus been shown to be erroneous.3. Attempts have been made to discover which of the receptor endings of the pars superior are involved in each of its functions, by eliminating separately the various endings. The results obtained are not entirely consistent. Production of the static reflexes and of the reflexes to centrifugal force and fast linear acceleration is in all probability the main function of the otolith organ (utriculus). It appears, however, that the assumption that the otolith organ is purely static in function is incorrect, for it has been shown that the utriculus can be involved in dynamic responses to rotations.The main function of the semicircular canals is the release of the dynamic reflexes. It has, however, been claimed that the vertical canals take part in the production ofstaticreflexes as well.Both the utriculi and the semicircular canals are involved in the maintenance of muscle tone.4. In the discussion of the general conclusions as to the function of the utriculi and of the semicircular canals it is shown that one of the important functional differences between the two receptors consists in their different reaction time, which may be due to the difference in their auxiliary structures and to a different pattern of their nervous connection with the effector organ

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00499.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY