ACTION OF THE FEMALE. 971 



elude that the attributes of the embryo will be influenced in a most important 

 degree by the entire condition (as relates both to the organic and the psychical 

 life) of both parents at the time of the sexual congress ; and it is probably on 

 account of the perpetual changes taking place in the bodily and mental state of 

 each individual (his condition at any one time being the general resultant of all 

 those changes), that we almost constantly witness marked differences between 

 children born at successive intervals, however strong may be the " family like- 

 ness" among them, whilst the resemblance between twins is almost invariably 

 much closer. 1 



976. Having thus noticed the principal points of the history of the develop- 

 ment and impregnation of the ovum, we shall proceed to consider the provisions 

 made for the Nutrition of the Embryo, through the generative apparatus of 

 the female, up to the time of parturition ; deferring the history of the develop- 

 ment of the ovum for that separate consideration which the importance of that 

 subject demands. About the time that the ovum is leaving the ovary, the cells 

 of the proligerous disk which immediately surrounds the zona pellucida become 

 club-shaped (Fig. 247) ; their small ends being applied to the surface of the 

 ovum, so as to give it somewhat of a stellate appearance. According to Bis- 

 choff, these cells entirely disappear from the ovum of the rabbit, as soon as it 

 has entered the Fallopian tube; whilst in the bitch they become round, and 

 continue to invest the ovum in this form throughout its whole transit to the 

 uterus. During its passage, the ovum acquires a sort of gelatinous envelop, 

 which is inclosed in a membrane of fibrous texture, termed the Chorion. This 

 envelop is probably of an albuminous nature in reality, corresponding with 

 the white of the Bird's egg : whilst the fibrous texture of the chorion seems to be 



Fig. 247. 



. An ovarian ovum from a Bitch in heat, exhibiting the elongated form and stellate arrangement of the 

 cells of the discus proligerus or membrana granulosa around the zona pellucida. B. The same ovum after 

 the removal of most of the club-shaped cells. 



produced, like the membranous basis of the eggshell of the bird, 3 by the exuda- 

 tion of fibrin from the lining membrane of the Fallopian tube or oviduct. The 

 outer layer of this envelop, in the egg of the bird, is consolidated by the de- 

 position of particles of carbonate of lime in its areolse ; and none of it under- 

 goes any higher organization. The Chorion of the Mammal, on the other 

 hand, subsequently undergoes changes of a much higher order ; which adapt it 

 for participating, to a most important degree, in the nutrition of the included 

 embryo. The first of these changes consists in the extension of the surface of 



1 This strong resemblance, it is true, is occasionally deficient; but this may perhaps be 

 fairly attributed to the circumstance of the twins being the offspring of different concep- 

 tions, which is undoubtedly sometimes the case, as is shown by the long interval that 

 elapses between their births ($ 990). 



2 'Trine, of Phys., Gen. and Comp.," g 160, Am. Ed. 



