177 



by uterine epitbelium iuto maternal tissue, but, as in other 

 Insectivora, by the progressive centripetal growth of troplioblast 

 and allautoic capillaries together. He mentions that the tropho- 

 blastic lacunae are liued by a 'pseudo-endothelium', and that the 

 deepest trophoblastic cells are phagocytic 'deciduo-fracts'. 



It is exceedingly hard to decide between these two very diver- 

 gent points of view; but I may perhaps poiut out that Strahl 

 admits that the epithelium is very thin and difficult to recog- 

 nise, that the reason why he has not seen the degeneration of 

 it is perhaps because he has missed the stage in which it occurs, 

 and that the figure (Fig. 15a) to which he especially refers is 

 not very convincing; he shows indeed a layer of dark nuclei at 

 the surface, but this layer is not continued over the villus. 



Vernhout on the other hand gives a figure of the actual dege- 

 neration of the epithelium. 



Strahl argues from the Carnivora to the Insectivora; I must 

 say that it seems to me, to say the least, to be equally permiss- 

 ible to argue from the Hedgehog and the Shrew to the Mole. 



Tarsius, Monkeys, and Man. 



Apart from the very numerous works on the human placenta, 

 the completest account that has been given of the placentation 

 of any Primate is Hubrecht's memoir on Tarsius (22). It is 

 necessary to poiut out here that not only in the histological 

 character of its placenta, but also in the arrangement of its foetal 

 membranes Tarsius agrees extraordinarily closely with Monkeys, 

 and Man, and difiers widely from the Lemuroidea. The yolk-sac 

 is diminutive, there is a large extra-embryonic coelom, there is 

 a vascular 'Bauchstiel' formed, as Hubrecht (23) has shewn, at a 

 very early period and in no way connected with the amnion- 

 folds. There is no free allantois. 



For such knowledge as we possess of the placentation of Monkeys 

 we are indebted to Turner (50), Waldeyer (53) and Selenka (39). 

 The earliest human embryos known are those described within 

 the last few years by van Heukelom (17) aud Peters (36); Webster 



