On the Female Organs and Placentaiion of the Racoon. 281 



Its one extremity was closed, and was attached to the central point of 

 placenta, immediately over the dorsal surface of the embryo. It will 

 be recollected that at this point the placental substance was deficient, 

 and to the margin of this deficiency the blind end of the sac in question 

 was closely adherent. The csecal extremity, however, did not project 

 through the aperture in the placenta, and consequently did not reach 

 the uterine surface of the latter. A careful examination of the blind 

 end of this sac showed that its outer surface was clearly continuous 

 with that portion of the allantoic membrane which lined the foetal 

 surface of the placenta. Hence we conclude that in P?vcyon, as in other 

 Carnivora, the reflection of the allantois from the inner surface of the 

 chorion to the outer surface of the amnion takes place originally at the 

 central point of the placenta, that is, from the margins of the placental 

 gap ; and that along with the amnion, although not separable as a 

 distinct structure, there is combined the inner or reflected layer of the 

 allantois. The other end of the sac was ruptured, and, extending 

 backwards (with reference to the embryo), was compressed between the 

 dorsal surface of the latter and the inner surface of the caudal pole of 

 the chorion. When distended with spirit this sac proved to be of such 

 a size that I had no difficulty in replacing the foetus in its interior. 

 Although from the ruptured condition and its abnormal position with 

 reference to the embryo, the resemblance of this sac to that of the 

 amnion was much obscured, I have little doubt that it must be 

 regarded as representing the latter. In favour of this view is the fact 

 that, unless it be so regarded, there was no other structure the arrange- 

 ment of which was in any way comparable to that of the amnion; and 

 conversely if it were not the amnion, and inasmuch as its relations 

 negatived the supposition that it could be the umbilical vesicle, we 

 should be compelled to assume that, in Procyon, we have a foetal mem- 

 brane of which there is no representative in any other Carnivore, the pla- 

 centation of which has been hitherto described. Moreover, the close 

 attachment of the blind extremity of this sac to the margins of the 

 central deficiency of the placenta lends additional support to this view. 

 Bischoff,* in his account of the placentation of the otter, refers to a 

 corresponding deficiency in the placenta of that animal. A similar 

 observation is recorded by him in respect of the placenta of Mustela 

 foina and Mustela martes.^ The presence of this gap in the placental 

 substance he explains by supposing that the separation of the false 

 from the true amnion takes place in these animals at a relatively later 

 date than in the majority of mammals; and that, consequently, an 

 obstruction is thereby occasioned to the investiture, by the vascular 

 allantois, of the foetal surface of the chorion, resulting in the deficiency 

 in question. In accordance with this view, the placental gap must 



* " Sitzungsbeiy der Akad.der Wissenseh./' Munchen, 4 Marz, 1865. 

 f Ibid., 13 Mai, 1865. 



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