摘要:

SummaryI. The vertebrate excretory system is a holonephros. The entire organ arises from the one source, namely, from the intermediate cell‐mass which unites the somite with the lateral plate, and is originally segmental. The part of the intermediate cell‐mass adjacent to the somite develops into the nephrotome or nephric chamber, and the part connecting it with the body cavity becomes the peritoneal canal. The tubule is an outgrowth from the dorsal wall of the chamber and the duct arises from the union, in front and behind, of the distal extremities of the tubules and is therefore primitively segmental.2. The simplest relations appear to be found in myxinoids so far as can be ascertained from the somewhat incomplete knowledge we possess of this group. They are also primitive in Gymnophiona and detailed reference has therefore been made to this group.3. The original terms pronephros, mesonephros and metanephros are retained. The term pronephros should only be applied to the organ in larval Anamnia and to that of a few adult teleosts. In most vertebrates, behind the pronephros where this is present, or posterior to the zone of anterior rudimentary tubules, the intermediate cell‐mass is early separated from somite and lateral plate and forms the so‐called nephrogenic blastema from which the remainder of the excretory organ is derived. The later differentiation is one of size and complexity only. The gradual separation of the hinder portion into a well‐defined isolated metanephros, such as is present in the Amniota, is indicated in some elasmobranchs and in some urodeles, and is seen in various species of teleosts.4. Recent experimental work with Amphibia has located the area from which the organ develops in the gastrula. The methods of pronephrotomy and transplantation have substantiated the earlier observations as to the precise level at which the pronephros arises and that from which the duct takes its origin. The capacity of the duct to grow independently backwards towards the cloaca has been conclusively proved by the use of vital staining. By means of bisection, partial removal and transplantation an attempt has been made to ascertain the power of regeneration of the duct and also the interrelations between the latter and the developing mesonephric blastema. Interesting information has been acquired with regard to the role of induction in these interrelations.5. Attention is drawn to the distinction between the ciliated nephrostomial canal and the ciliated peritoneal canal; their initial derivation and later development in normal and abnormal conditions is discussed.6. The relationship between external and internal glomeruli is considered, and the passage from one to the other as met with at the anterior end of the mesonephros in many Amniota is described. It is emphasized that the function of such a condition is by no means clear and needs experimental investigation.7. It is concluded that the homogeneity of the pro‐, meso‐ and metanephros has now been convincingly established from many points of view. The nephrogenic material arises from a single source and exhibits identical properties throughout, and there is striking uniformity in the structure and function of the various parts

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb00589.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Summary.1. As Pearl (1926) recognized, theDrosophilaculture can be taken as a model of population growth involving the interaction of a plant and an animal species. Early work suggested that the growth of the fly population could be adequately described by an S‐shaped curve of the kind previously applied by Verhulst (1839) to human populations. This curve, the logistic, shows that populations apparently possess:(a)a slow initial growth rate, which(b)increases until it reaches a maximum (the point of inflexion of the curve), and(c)then becomes progressively less as the population approaches the maximal size possible under the particular ecological conditions. This logistic law was subsequently widely applied to a variety of populations, from bacterial to human, developing under divers conditions. Part of the justification for this procedure derived from the apparently fundamental character of theDrosophilamodel, and this review is devoted to an examination of that assumption.2. The mathematical derivation of the Pearl‐Verhulst logistic law is shown to rest on highly arbitrary postulates which are not supported even by the early experimental analysis of the circumstances influencing natality and mortality in aDrosophilaculture. Pearl and his co‐workers generally failed to recognize the importance of the growth of the yeast population, and, by paying attention only to the adult flies in their cultures, took no account of the contribution of the larvae and pupae present to the total population. As a consequence, their formulation of the experimental analysis was in terms of the intraspecific relationships between the adult individuals ofDrosophila, and little weight was attached to the competition between larvae for food and space.3. Examination of the total population (eggs, larvae, pupae, adults and yeasts) present in a culture shows that the logistic has sometimes been applied to family growth and not to true population growth, and that it describes even this restricted phase very incompletely. The precise course of population growth is found to depend upon the changes of egg output of the females, pre‐adult mortality and the duration of the various instars. Each of these is affected to some extent by the availability of the yeasts, and the growth and distribution of the yeasts is modified by the activity of the feeding larvae in the culture. That is, the interspecific relationship is found to be the primary ecological regulator of population growth; but the data from a total count are not sufficiently precise to permit a detailed analysis of this relationship.4. While the course of oviposition of normal females is fairly regular under optimal conditions, their potential fecundity is more than halved when they are introduced into a normal culture bottle. This reduction in egg output results from a change in the character of the yeasts, a qualitative change, induced by the activity of the larvae in the medium. Since the yeasts change quantitatively and qualitatively as the culture grows, the early experiments on the fecundity of adults crowded under optimal conditions have little relevance to the analysis of population growth. Indeed, it has been shown that this decline of fecundity with crowding is mainly a consequence of food shortage, and such a shortage is only likely to affect the second generation of adults in a culture. The viability of the eggs that are laid changes, in much the same way as the oviposition rate, as the females age, and it also is affected by the quality of the yeasts available to the flies.5. The feeding activity of the larvae causes a progressive physical breakdown of the agar‐gel medium, and it is thought that this alteration causes the yeasts to change from a predominantly aerobic to an anaerobic form of respiration, and thus to change their qualitative characteristics. At the same time the yeasts grow, and are carried by the larvae, thus spreading through the medium. So the larvae hatching from the eggs find themselves under different conditions as the culture develops. These differences in the state of the medium, in availability and kind of yeasts and the numbers of other larvae of various ages present, result in a progressive, if irregular, slowing down of pre‐adult development rate and in an increase of pre‐adult mortality. Even during the phase of family growth this mortality may amount to 20–30%. Further, the flies hatching will have had their potential fertility modified by the conditions under which they developed, and this is likely to be of particular significance for the flies hatching out during the later stages of family growth. It is not surprising, then, that the number of adults found in a culture depends very much on the kind of medium used, and on the quality of yeast seeded on to it, or that the course of the growth of the adult population is also very variable and can only rarely be described as logistic.6. The significance of these findings for ecological theory lies mainly in the emphasis it places on the inter‐specific relationship described, which is much more complex than the simple competition between adult flies previously taken as the main factor determining population growth. Part of this complexity arises from the qualitative alterations occurring in the yeast population, and it is shown that these may be important in work on selection and for other genetic experiments. However, the ecology ofDrosophilain nature may involve even more complex reactions, some of which may be of greater significance than those described for laboratory populations. Field and laboratory experimental work could be profitably carried through together

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb00590.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Summary1 In an ecological classification of the soil fungus flora, a number of groups can be distinguished, such as obligate saprophytes, root infecting fungi and fungal parasites of animals. This article has been concerned with the ecological relationships between root infecting fungi and obligate saprophytes. The specialized plant parasites, together with mycorrhizal fungi (symbionts), have been grouped together asroot inhabiting fungi.The remainder of the root infecting fungi, together with the obligate saprophytes, have been designated assoil inhabiting fungi.2. The root inhabiting fungi are characterized by an expanding parasitic phase on the living host plant, and by a declining saprophytic phase in its absence. This restriction of the saprophytic phase of such root inhabitants is enforced by the competition of other soil micro‐organisms, and they can therefore be considered asecologically obligate parasites, inasmuch as their continued survival is dependent upon that of their host plants. With few exceptions, such fungi can readily be grown as saprophytes in pure culture and they are not, therefore, obligate parasites in the strict nutritional sense.3. The soil inhabiting fungi are characterized by ability to survive indefinitely as soil saprophytes. Some characteristics suggested as contributing tocompetitive saprophytic abilityare a high growth rate, excretion and tolerance of antibiotic toxins, and a capacity for rapid and complete decomposition of dead plant tissues.4. Some distinguishing characteristics for the separation of these two groups of organisms have been listed. Root diseases caused by soil inhabiting fungi are most important in seedlings, and in older plants in which normal host resistance has been impaired by an adverse environment. Diseases of annual crops caused by such fungi are less amenable to control by crop rotation than are those caused by root inhabiting fungi.5. Evolution of the host‐parasite relationship is suggested as the determinant in the segregation of root inhabiting fungi. Competitive saprophytic ability is incompatible with such evolution, and is gradually lost, but the sheltered host‐borne phase of the root inhabitant is prolonged. Evolution appears to have progressed furthest in the mycorrhizal fungi, as evidenced by their loss of competitive saprophytic ability, which has culminated in the nutritionally obligate parasitism of the vesicular‐arbuscular endophytes(Rhizophagusspp.).6. Interference by other soil micro‐organisms with the parasitic activity of a root inhabiting fungus is greatest at the root surface, where the soil micro‐flora is greatly intensified, and is also changed in composition, by root excretion and by other activities of the living root. The rhizosphere and root surface microfloras thus appear to constitute the root's outermost barrier against invasion by pathogenic fungi.7. In its invasion of the host root, a root inhabiting fungus is likely to be accompanied or followed by weak secondary parasites and obligate saprophytes. With progressive improvement in the relationship between host and primary parasite, gross disorganization of host root physiology and defence mechanisms is likely to diminish, and so the infected root may still be able to repel secondary invaders. Thus the ectotrophic mycorrhizal symbiosis is typically a closed association, and functions as a symbiosis for defence as well as for nutrition.8. The saprophytic survival of a root inhabiting fungus in dead infected host tissues is curtailed by the competition and antagonism of associated saprophytes, and is likely to be shortest under soil conditions optimum for microbiological activity.Grateful acknowledgement is made to the Agricultural Research Council for their provision of a research grant, during the tenure of which this article was prepared. I am especially indebted to Dr J. Rishbeth, both for permission to quote from his data onFomes annosusbefore publication and for much helpful discussion on root disease problems, and to Prof. F. T. Brooks, F.R.S., for his valuable comments on the

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb00591.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Résumé1. La calorification des hibernants endormis est de2,0 à 2,5 Calories par kilo et 24 heures pour les espéces dont le poids oscille entre 200 et 2200 g. Les deux espéces étudiées a la même température (10oC.) qui ne péssent que 20 g. (muscardin et chauve‐souris) ont une calorification ?intensitéá peu prés double.Quand on raméne la production de chaleur des hibernants á la surface (S = 10 × P½), on constate que les especes de 20 a 250 g. (chauve‐souris, muscardin, loir, spermo‐phile) produisent environ12,5 Calories par métre carré et 24 heures, tandis que les marmottes de 850 á 2000 g. en produisent à peu prés deux fois autant.2. La calorification des hibernants endormis obéit à la régie de van't Hoff‐Arrhénius entre 8 à 10oC. Les hibernants endormis ont tendance à se réveiller aux températures voisines de ooC.3. Au point de vue quantitatif, il semble qu'il soit difficile ?éablir une différence fondamentale entre la calorification des mammiféres hibernants endormis et celle des vrais poikilothermes (reptiles, amphibiens) mesurés à la même température de 10o.4. La chauve‐souris se comporte pendant toute ľannée comme un animal à température variable. Elle n'atteint une température centrale éléven (37o) et une calorification intense, comparable à celles des autres mammiféres homéothermes, en été que le soir au moment de son vol.5. Les hibernants endormis brûlent des graisses pour couvrir leur dépense ?énergie.6. Les hibernants endormis ne réagissent pas par de ľhyperventilation aux petites augmentations de la concentration en anhydride carbonique du milieu. lls présentent une respiration périodique. Ces deux manifestations prouvent que ľappareil de regulation de leur respiration est déprimé pendant le sommeil.7. Les hibernants réveillés ont une calorification en été qui est du même ordre de grandeur que celle des mammiféres homéothermes de méme taille. Leur production de chaleur obéit à la loi des tailles; la loi des surfaces s'applique à eux avec la même précision trés relative que Ton trouve chez les autres homéothermes.8. La thermogenése de réchauffement des hibernants réveillés est particuliere‐ment intense; ce fait est dû a leur mauvaise régulation de la déperdition. Les hibernants révéilles ont toujours une thermorégulation physique insuffisante.9 En automne, on voit apparaître une réduction de la thermogenése de réchauffement. ľentrée en sommeil hibernal est précedée ?une insuffisance thermo‐régulatrice intéressant et les mécanismes de thermolyse et ceux de thermogenése.s10. Les hibernants présentent un cycle annuel ?un grand nombre de glandes endocrines: hypophyse antérieure, glandes génitales, cortex surrénalien, thyroide présentant des signes ?involution automnale avec maximum ?activité au printemps (mars). La duree de ľhyperactivité thyroidienne est courte. II est trés probable que la température élévee de ľété, le grand développement de ľactivité génitale, sont responsables de ľinvolution thyroidienne relative, déjá manifeste en avril et mai.Le cortex surrénalien présente une zone X trés développée de 1'automne au printemps. Elle se manifeste aussi bien chez les mâles que chez les femelles. En fin de printemps et en été, la zone X n'a qu'un aspect vestigial.La médullaire surrénale présente pendant toute ľannée une grande variabilityé de sa teneur en adrénaline. Nous interprétons ce fait comme traduisant un décalage possible entre ľélaboration et ľélimination de ľadrénaline.Les îlots de Langerhans présentent aussi un cycle annuel: en hiver, on ne trouve‐que des cellules à insuline, en été, on observe la présence de deux types cellulaires. Pendant ľhiver, il n'y a certainement pas réduction de la fonction insulino‐secrétoire du pancréas.Les parathyroides présentent, à leur tour, un cycle annuel. II est impossible de reconnaître dans les parathyroides une insuffisance fonctionnelle en hiver.11. La glande hibernale est du tissu graisseux de réserve avec présence de glycogéne. II est probable qu'il peut y avoir, sur place, transformation de glucides en lipides.12. ľon peut réussir à maintenir pendant prés ?une année un aspect hibernal des glandes endocrines en conservant 1'hibernant à basse tempéarature et en le soumettant à un jeûne complet ou partiel. Pendant tout ce temps, ľhibernant doit, sa respiration et sa calorification ne différent pas de celles enregistrées en hiver.13. L'ablation de ľhypophyse en été, associée ou non à la destruction des médullaires surrénales, àľinjection ?hypnotiques et narcotiques hypothermisants (nembutal, chlorure de magnésium) ou ?insuline, provoque une chute de la température centrale des hibernants maintenus à 5oC. avec un état de torpeur comparable à celui du sommeil hibernal. Mais la mort des animaux, survenant dans les trois jours, nous fait conclure que ľétat particulier qu'entraîne 1'intervention n'est qu'une imitation lointaine du sommeil.14. Nous pensons que la différence entre ľétat de sommeil hibernal vrai et celui induit par ľhypophysectomie ou les hypothermisants réside dans une différence entre ľétat ?excitabilité du systéme n

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb00592.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY