FCETAL NUTRITION: THE PLACENTA 497 



man appear to be engaged in disintegrating mucosal tissue, and 

 producing a zone of coagulation necrosis, i.e. a symplasma, around the 

 trophoblast. But they differ from similarly situated cells in lower 

 animals, e.g. the mouse, in showing no evidence of ingestion of formed 

 tissue-elements. 



In the youngest ova no space exists between the trophoblast and 

 the wall of the implantation cavity (Fig. 152). In later specimens 

 a space is formed, apparently by the absorption of the debris of the 



FIG. 151. Section of a portion of the necrotic zone of the decidua, and of 

 the layer of large cells on its inner aspect. (Bryce and Teacher.) 



nz., Necrotic zone ; me., large cells in various stages of degeneration ; 

 car., blood-filled implantation cavity. 



necrotic zone. How this excavation is brought about is uncertain. 

 According to Peters, the trophoblast may exercise a phagocytic 

 action. Bryce and Teacher, however, found no evidence of such "a 

 process, and inclined to the opinion that the material was dissolved 

 by an enzyme before its absorption. In the trophoblast they found 



Kolster and Disse maternal, and Jenkinson both foetal and maternal. In the 



fuinea-pig, v. Spee states that they are foetal. In the hedgehog they were 

 rst described by Hubrecht as maternal, and later as foatal. In man, as stated 

 above, the same doubt exists whether the trophoblast consists 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." 





