摘要:

Summary.1. The two series of observations on Cladocera showing (a) that a state of depression produced by unfavourable external conditions inDaphniafemales kept in cultures causes a change from parthenogenetic to gamogenetic propagation, and (b) that gamogenesis in nature is accompanied by a state of depression in the populations in question, go to prove the correctness of the hypothesis that in nature the transition from parthenogenesis to gamogenesis is caused by the influence of unfavourable external conditions. Unfavourable external conditions cause states of depression in the females and thereby the change in the mode of reproduction and so also a change in sex determination. (Section II.)2. A number of earlier and more recent laboratory experiments have given results which support this depression hypothesis. (Section III.)3. Investigations in nature on parthenogenesis and gamogenesis in the Cladocera and simultaneous observations on other functions in these animals likewise afford support for the depression hypothesis. (Section IV.)4. The reproductive cycle of the Rotifera is compared with that of the Cladocera. There is a good deal of evidence which would seem to indicate that in the Rotifera transition from parthenogenesis to gamogenesis—and so also the sex determination associated with it—is likewise caused by a state of depression, and that this state of depression may be induced by the influence of various external factors. (Section V.)5. A general survey is taken of some of the biological peculiarities characterising the state of depression associated with the change from parthenogenesis to gamogenesis. (Section

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01001.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY

摘要:

As yet we know comparatively little about haemocyanin. especially with regard to its relation to oxygen. It is a matter which would well repay investigation to determine whether it has the remarkable properties which haemoglobin has in this respect. properties which are at present unique. (Bayliss,Principles of General Physiology, 1915.)Summary.The haemocyanins are proteins combined with a prosthetic group consisting of a complex copper salt of a sulphur compound and a polypeptide. The physical and chemical properties of haemocyanin are largely due to its protein nature, and the specific differences between the haemocyanins of different groups of animals result largely from the differences in the protein part of the molecule. The combination of haemocyanin with oxygen and the characteristic change in the absorption spectrum which results are, on the other hand, properties of the prosthetic group. The haemocyanin combines with oxygen in all cases in proportion to its copper content, one molecule of oxygen being combined by a quantity of haemocyanin containing two atoms of copper. There is some evidence that at least two modifications of the prosthetic group may occur characterising the Crustacea and cephalopods on the one hand, and the gastropods andLimuluson the other. The equilibrium with oxygen may be described by the mass law if it be assumed that under different conditions one, two, or four prosthetic groups must be oxygenated simultaneously in order to form a stable compound and that under certain conditions a mixture of such forms of the protein exist. In general the oxygenation phenomena displayed by haemocyanin differ from those of haemoglobin only in a quantitative sense.The copper of the prosthetic group is in the cuprous condition but may be oxidised, forming methaemocyanin, by strong agents. Methaemocyanin will combine reversibly with oxygen, forming oxymethaemocyanin. Haemocyanin also combines with carbon monoxide, nitrogen dioxide and with cyanide, forming stable compounds.The physiological function of haemocyanin as a respiratory pigment is well established in the case of the cephalopods. Some correlation exists between the activity of various animals, the oxygen capacity of the blood, and the pressures of oxygen under which the haemocyanin becomes oxygenated.

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01002.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY

摘要:

Summary.The Galapagos Islands possess a peculiar and highly characteristic fauna and flora. The abundant bird and reptile populations are nearly all of endemic species; of the land birds only two species occur elsewhere than in these islands. Studies bearing upon the origin of the Galapagos fauna have led to diverse conclusions; scrutiny of modes of variation has revealed some curious situations. The Galapagos have been variously regarded as the surviving remnants of a land‐mass, now sunken, that was formerly connected with the American mainland, and as oceanic islands that have appeared above the ocean as the result of volcanic upheaval. Study of the birds is confirmatory of the latter view. The avifauna is clearly not derived from the South American mainland directly to the eastward. Of the marine species there are one or two of southern origin, borne northward on the cold Humboldt current, and there are others which constitute local forms of species that are of world‐wide distribution. There is an important element definitely recognisable as of West Indian derivation, and others may have originated from the same source. There are a few species that clearly are not of West Indian ancestry, and there are a number that are too widely differentiated for recognition of their immediate affinities. The hypothesis is advanced that the inception of the Galapagos avifauna took place in a period when North and South America were separated by the sea; the relationship of the faunas of the West Indies and the Galapagos is to be regarded in the same light as relationships from one to another of the West Indian islands. The bird population of the Galapagos, abundant as regards individuals, is, as regards representation of different groups, of the sparse and miscellaneous character to be expected of chance‐controlled wanderers to distant islands.Conditions are uniform enough throughout the archipelago, so that, with much local variation, each island contains a fair representation of the same general assemblage of species. Trends of variation are seen in arrested stages of plumage in certain species, in a possible tendency to melanism in others. There are many variants of these situations. The outstanding group of birds is the endemic family, the Geospizidae, including 37 species and sub‐species out of the entire list of 89 breeding birds. Extensive variation and complicated relationships within this family are such as can probably not be duplicated in any mainland stock of birds. The observed variation presents difficulties to classification, and certain trends of development seem to act independently of natural selection. The Geospizidae afford a fine example of diversification unhindered by comp

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01003.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY

摘要:

Résumé.The formation of exo‐enzymes may be shown in the case of bacteria by centrifuging off the organisms, with or without filtration, through a suitable filter candle or Seitz asbestos filter, and incubating with the appropriate substrate at the required pH. Further concentration and purification may be carried out by evaporationin vacuoat low temperatures (Hladik, 1910), fractional precipitation with ammonium sulphate (London and Pakhotina, 1917), precipitation, dialysis and re‐precipitation with alcohol (Munter, 1910), adsorption on alumina or kaolin and fractional elution with suitable buffers of selectedpH(Willstätter, 1928; Hopkins, 1930), dialysis (Harden and Young, 1906; Walter, 1917), and extracting with glycerine (Macfadyen, 1892).With moulds and actinomycetes the mycelium may be filtered off through paper and suitable methods of concentration applied to the filtrate. For the preparation of endo‐enzymes of bacteria, autolysis may be used, alternative freezing and thawing (Young, 1929), grinding in an agate mortar (Stevens and West, 1922,a, b), or lysis with bile (Avery and Cullen, 1923). For yeasts and fungi the “acetone‐dauerhefe” process employed by Dox (1913), combined grinding and extraction of juice by high pressure (Buchner, 1898), and low temperatures (Rowland, 1910), are available, after which further precipitation may be carried out. Halderer (1909, 1910, 1912) investigated the conditions influencing filtration of enzymes through porcelain filters. Two interesting recent methods of following protein hydrolysis are by Krebs (1930) and Gates (1930). The former dissolved the protein in bicarbonate solution in the cup of a Warburg manometer in the presence of 5 per cent. carbon dioxide. As hydrolysis proceeds the carbon dioxide tension changes and may be read off on the manometer. Gates measured the reduction in density of exposed photographic film in a photometer, progressive proteolysis of the gelatin leading to release of silver. Viscometric methods are well adapted to the study of breakdown of gelatin (von Gröer, 1912; Haines, 1933). A nephelometric method of following proteolysis has been developed by Rona and Kleinmann (1928). Foreman and Graham‐Smith (1928) worked out titration methods for following the changes in meat broth during growth ofStap

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01004.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY