摘要:

SUMMARY.1The rate of contraction of the red chromatophore of the shrimp is influenced by temperature and by the concentration of eyestalk extract.2The initiation of chromatophore activity requires a definite minimum concentration of eyestalk extract; the concentration necessary varies with temperature. Above this threshold concentration, the response of chromatophore cells at a given temperature is the same for different concentrations of extract.3When the conditions necessary for the initiation of the chromatophore activity are fulfilled, an increase in temperature from 15.6° to 20.7°C. results in a linear increase in the rate of chromatophore contraction. Above this temperature the rate of contraction is constant and independent of temperature up to 30°C.4Chromatophore cells in extracts of a concentration lower than the threshold value behave like controls in pure Ringer. They remain in the wholly dispersed state for a considerable length of time, without showing any sign of pigment concentrati

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1945.tb00857.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

SUMMARY.1Examples of Polecats, Polecat‐Ferrets, Ferrets and hybrids have been examined, and details of skulls and teeth are given.2It is considered that Ferrets may have skulls with an unconstricted waist, but that they will have smaller carnassials than wild Polecats.3Ferrets may be as large as the largest Polecat.4It is suggested that, in view of the distinctions between the Scottish and Welsh Polecats, both of which, like Ferrets, incline more to theP. putoriusthan P.eversmannitype of skull, Ferrets in this country have had a dual origin, the present strain being a mixture of the tw

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1945.tb00858.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

SUMMARY.1An account is given of the morphology of the respiratory system ofMelophagus ovinus.2The respiratory movements of the abdomen in the male and the female are described.3The function of the respiratory system is discussed and the probable respiratory mechanism is deduced from the morphological data.4Experiments in which the rate of entry of ground derris root into the tracheal system is used as a measure of the rate of breathing show that mechanical ventilation of the tracheal system normally takes place in the ked. Respiratory movements of the abdomen produce a directed flow of air passing in through the abdominal spiracles, over the intra‐tracheal valves in the anterior region of the dorsal longitudinal tracheæ, and out through the thoracic spiracles.5Experiments comparing the rates of respiration of male and female keds are described. It is found that the sexual modifications of the respiratory system which have arisen in the female do not increase the volume of air respired, although they may induce a more perfectly directed flow of air than in the male. It is thought that they ensure a plentiful supply of oxygen and adequate growing space for the larva which remains relatively undisturbed by the pumping movements of the abdomen.6The spiracular rhythm of the prothoracic spiracle is correlated with the respiratory movements of the abdomen. The effect of carbon dioxide and oxygen on the spiracular rhythm is demonstrated.7Experiments with both derris and inert dusts show that at high rates of respiration the amount of dust entering the tracheal system is governed by the structure of the spiracle, the particle size of the dust, and the volume of air inspired in a given time. At low rates of respiration the number of spiracles operating is of importance.8It is shown that the abdominal spiracles afford greater protection against the entry of dust into the tracheal system than the thoracic spiracl

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1945.tb00859.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

SUMMARY.1The changes in the uterine wall preceding and during the process of implantation of the blastocysts are described. The formation of the uterine crypts results from rearrangement of the cells of the uterine epithelium and they open into the uterine lumen from the time of their inception. This account differs from Hubrecht's (1894), who claimed that the crypts were formed from nests of epithelial cells beneath the epithelium which acquired a secondary opening by the breaking clown of the overlying epithelium.2The changes in the structure and arrangement of the embryonic membranes during and after the attachment of the blastocyst to the uterine wall are described in sequence.3Amniogenesis is by fold formation after the embryonic plate has been exposed by the disappearance of the cells of Rauber. The amniotic and chorionic parts of the folds are distinct from the beginning and there is no transformation of the one into the other. A transient sero‐amniotic connection is formed from the cells of the amniotic wall of the folds at the point where they close, far back over the embryo. The proamnion is large and is invaginated, together with the yolk‐sac, by the formation of the cervical flexure. The mesoderm only extends into this region at a late stage in development.4The allantoic mesoderm differentiates very early, almost immediately after the formation of the exocoel. The entodermal allantoic diverticulum is formed later, is exceedingly rudimentary and transitory. The allantoic stalk is not provided with a trophoblastic sheath, like that ofCrocidura(Sansom, 1937). The allantoic mesoderm fuses with the chorion, forming the allantochorion, very soon after the closure of the amniotic folds, and the adherence of the ehorionic trophoblast to the mucosa.5Vestiges of a decidua capsularis corresponding to that ofErinaceusare found inSorex, but a complete decidua eapsularis is not formed. Small transitory folds, which are quite distinet from the vestiges of the decidua capsularis, are, found inSorex araneusand it is suggested that these correspond to the so‐called “ decidua eapsularis ” ofCrocidura.6Reichert's membrane is well developed in the Shrews. It is formed between the mesoderm and trophoblast of the chorion and between the entoderm and trophoblast of the bilaminar omphalopleure. Therefore it appears to be of purely trophoblastic origin. It disappears in the placental region after the establishment of the allanto‐chorion. Later its free margin forms a supporting collar around the base of the allantoic stalk.7The whole of the upper or splanchnic wall of the yolk‐sac is invaginated within the lower or bilaminar wall so that the sinus terminalis runs around the rim of the cup so formed. The entodcrm cells of the area vasculosa become enlarged and their cytoplasm charged with granules. The small blood vessels of this region project into the cavity of the yolk‐sac, forming villi which are covered with these enlarged entoderm cells and apparently are absorptive organs. The yolk‐sac remains large and its bilaminar wall persists throughout development, though its cavity is greatly reduced by invagination and the consequent approximation of its oute

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1945.tb00860.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

ISSN:0370-2774    

DOI:10.1111/j.1096-3642.1945.tb00861.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY