FCETAL NUTRITION; THE PLACENTA 497 



mail appeal- to Ije engaged in disintegrating inucijsal tissue, and 

 producing a zone of coagulation necrosis, i.e. a sj-mplasma, around the 

 trophoblast. But the}- differ from siniilarl)' situated cells in lower 

 animals, &(/. the mouse, in showing no evidence of ingestion of formed 

 tissue-elements. 



In the youngest o\a no space exists l)etween the tropholjlast and 

 the wall of the implantation cavity (Fig. 1.j2). In later specimens 

 a space is formed, appaiently by the al>Ror])tioii (if the di'luis of the 





mc 



Fig. 1.^1. — Section of a portion of the necrotic- zone of tlie decidua, and of 



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



«2., Necrotic zone ; mr., large cells in various stages of degeneration ; 



ear., blood-fiUecl implantation cavity. 



necrotic zone. How this excavation is brcaight alxiut is uncertain. 

 According to Peters, the tropholilast may exercise a phagocytic 

 action. Bryce and Teacher, howe\-er, found no e^ddence of such a 

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

 by an enzyme before its alisorption. In the tropholilast they found 



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

 guinea-pig, v. Spee states that they are fcetal. In the hedgehog they wei'e 

 first described by Hubrecht as maternal, and latei- as f(etal. In man, as stated 

 aljove, the same doubt exists whether the trophoblast consists of two la3'ers, 

 cytoblast and plasniodiblast, oi- possesses a thiid layer composed of laige cells, 

 and forming the advance guaid in attacking the uterine mucous membrane and 

 enlarging the "Eikammer." 



