XI 



SOME RECENT EMBRYOLOGICAL 

 INVESTIGATIONS 



THE close resemblance between the embryos of 

 animals which, when adult, are widely different 

 in form, in size, and even in structure, greatly 

 impressed the earlier embryologists, and was often 

 insisted on by them. A reptile, a bird, and a 

 mammal are in their early stages of development 

 so closely similar that v. Baer himself was unable 

 to decide to which of these groups three unnamed 

 embryos in his collection were to be referred. 



A still more striking illustration is afforded by 

 the controversy which raged for many years over 

 Krause's famous embryo. In 1875 Krause de- 

 scribed an early human embryo which appeared to 

 differ from all known human embryos in having 

 a large vesicular allantois like that of a chick or 

 reptile, instead of the thick allantoid stalk by 

 which the human embryo is normally connected with 

 the chorion. This peculiarity with regard to the 

 allantois was so marked that doubts were at once 



