io 4 SPECIAL CONVERGENCE 



activity usually accompanied by great increase 

 in the size of the blastocyst. 



Similar simplification and change of function 

 leading to parallel results have occurred in other 

 orders of mammals, e.g., in certain Edentates 

 (Manis the pangolin, or scaly ant-eater) and in 

 the Lemurs. Hubrecht expresses the hope that 

 his discussion of the facts will prevent any future 

 attempt to place Ungulates and Lemurs on the 

 same level of so-called primitive placentation. 



In the same way the old hypothesis which 

 maintained that the early villiferous state of the 

 human blastocyst, in the phase called " Reichert's 

 ovum," recapitulates ontogenetically a diffuse 

 phase to which the discoid stage succeeded 

 later, ought to be discarded, because, inter alia, 

 Reichert's ovum is enclosed by a decidua reflexa 

 seu capsularis, and is not freely suspended in the 

 uterine cavity as are the blastocysts which show 

 diffuse placentation. Furthermore, Hubrecht 

 adds that this "phenomenon of encapsulisation 

 inside the mucosa has appeared independently 

 in more than one order of mammals." The 

 arrangement in question, by which the develop- 

 ing blastocyst is withdrawn from the uterine 

 lumen and enclosed by a decidua capsularis, has 

 been realised in man and anthropoid apes, in 

 different genera of rodents, in the spiny hedge- 

 hog Erinaceus, in the spineless Malayan hedge- 



