470 THE PHYSIOLOGY OF REPRODUCTION 



V. Heukelom described the cellular layer outside the syncytium 

 as foetal, and derived from Langhans' layer. 1 Whatever their 



* .. :: 

 % *.*, 



j * 



dec 



end 



%,^ 

 * * * 



.^w 



FIG. 123. Section of a portion of the wall of the human blastocyst. 

 (Bryce and Teacher.) 



cyt., cyto-trophoblast ; dec., decidua ; end., endothelium of maternal capillary ; 

 pi., plasmodium ; nz., necrotic zone of decidua. 



1 Much uncertainty still exists regarding the origin of these large cells 

 in Man and other animals. In the mouse, Duval and Sobotta consider them 

 foatal, Kolster and Disse maternal, and Jenkinson both foetal and maternal. 

 In the guinea-pig, v. Spec states that they are foetal. In the hedgehog 

 they were first described by Hubrecht as maternal, and later as foetal. In 

 Man, as stated above, the same doubt exists whether the trophoblast con- 

 sists of two layers, cytoblast and plasmodiblast, or possesses a third layer 

 composed of large cells, and forming the advance guard in attacking the 

 uterine mucous membrane and enlarging the " Eikammer." 



