THE PLACENTA. 445 



tissue. Owing to the strong contraction of the muscles of the 

 uterus at the time of birth of the young, the bare patch, from 

 which the placenta has been separated, is at once greatly re- 

 duced in size, while the loosely attached mucous membrane 

 of the obplacental region slips over it, and closes the wound 

 almost instantly. The complete regeneration of the uterine 

 epithelium after parturition is effected with astonishing rapidity, 

 and the doe is ready to receive the buck almost immediately 

 after she has given birth to the young. 



The placenta is commonly regarded as essentially an allantoic 

 structure. But the facts, that the attachment to the uterus is 

 first effected, not by the allantois, but by the epiblast of the 

 blastodermic vesicle ; and that the allantois merely utilises this 

 attachment as a means of getting access to the uterus, suggest 

 that the participation of the allantois in the formation of the 

 placenta is probably a secondary and not a primitive character. 



The further fact that changes occur in the mucous membrane 

 of the obplacental and periplacental regions, similar to the earlier 

 changes seen in the placental region, suggests that the area of 

 attachment of the blastodermic vesicle to the uterus was origin- 

 ally a more extensive one. Minot has contended, from these 

 and similar considerations, that the mammalian placenta was 

 originally formed from the chorion, i.e. from the extra- embryonic 

 part of the blastodermic vesicle, and not from the allantois ; 

 and the history of the formation of the placenta in the lower 

 groups of Mammals strongly supports this view. 



List of the more important Publications dealing with the 

 Development of the fiabbit. 



Barry. M. : ' Kesearches in Embryology.' Philosophical Transactions of the 

 Royal Society. 1840. 



Beneden, E. van: Recherches sur la Composition et la Signification de 

 1'CEuf.' Bruxelles. 1870. 



' Recherches sur 1'Embryologie des Mammiferes. La Formation 

 des Feuillets chez le Lapin.' Archives de Biologic, i. 1880. 



' Observations sur la Maturation, la Fecondation et la Segmenta- 

 tion de 1'CEuf des Cheiropteres.' Archives de Biologic, i. 1880. 



Beneden, E. van, and Julin, C. : ' Recherches sur la Formation des Annexes 

 Fcetales chez les Mammiferes.' Archives de Biologie, v. 1884. 



Bischoff, T. L. W. : ' Entwicklungsgeschichte des Kaninchen-Eies.' Braun- 

 schweig. 1842. 



