the human ovum, the entire uterus is covered by a thick 

 layer of coagulated matter, the caudal membrane. Baer, follow- 

 ing Hunter, 5 repeated that this membrane forms a pocket in 

 which the ovum lies in an open sac, a peculiarity which 

 distinguishes humans from other mammals. 



Returning to the question about the origin of the ovum, 

 Baer recalled the unsuccessful searches for mammalian ova by 

 Haller and his student Kuhlemann, the observations of Cruikshank, 

 and his own investigations, leading to the discovery of the ovum 

 in the Graafian follicles. The history of this discovery is 

 considered above (in Chapter 14). 



After a description of the female genital system in 

 mammals, Baer addressed the characteristics of the ovum in the 

 ovary. On this question, Baer could not reach complete 

 clarity. In his opinion, the follicle content is a fluid 

 rich in protein, surrounded by a granular membrane, which he 

 erroneously compared with the vitelline membrane of bird's 

 egg. In the albuminous fluid Baer saw vitelline globules 

 and therefore considered it possible to call the follicle 

 content an ovum, noticing, however, that it represents some- 

 thing more than the yolk ball of a bird's egg, because not 

 all the mass covered with the granular membrane is converted 

 into the fetus. The embryo of mammals is developed from a 

 small vitelline globule situated at the inner surface of the 

 follicle and ejected after the latter bursts „ This globule 

 Baer compared with the embryonic vesicle in the eggs of birds 

 and reptiles. He recognized, however, some consequences of 

 this comparison, noticing that in birds and reptiles the 

 embryonic vesicle in the fertilized egg disappears, while in 

 mammals it is the beginning of the embryo. 7 Further Baer 



Baer referred to a treatise by (William) Hunter, 

 ANATOMIA UTERI HUMAN I G RAVI DAE TABULIS 

 ILLUSTRATA, Birmingham, 1774. 

 See also Baer, NACHRICHTEN, p. 331(323). 

 There Baer stated his polemics with Plagga, attempting 

 to ascribe to himself the priority of the discovery of 

 the ovum of mammals. 



Detailed analysis of Baer's errors connected with the 

 study of the mammalian ovum is given by P. G. Svetlov 

 in his remarks on the translation of the second volume 

 of UBER ENTWICKLUNGSGESCHICHTE (remark 139, 

 pp. 476-479) . 



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