AND THE EOF/I'AL MEMT.llAXES, TX THE ('HTOK'. 3^5 



from th(^ body w:>li <>ii tliat side of the amniotic mesoblast which is 

 tnriied towards the e])il)last in the manner already described by Schenk/ 

 Tliis net-work advances hand in hand with the stratification of the 

 epiblast, and tlie mesol)Iastic net-work also scarcely reaches the sero- 

 aniniotic coniiectii^n before the amnion closes np (Fig. 90). 



The strati ti cation of the epiblast and the reticulation of the 

 mesoblast spread firther in later hours of the incubation. At the end 

 of the fourth day, the mesobListic net-work has already reached the 

 sero-amnititic connertion and |)assed along both sides of it towards the 

 serous envelo])e over which it also gradually spreads (Figs. 71 and 

 7.')). Distinct stratification of the epiblast is also found from the same 

 jK'riod in the amnion as well as in the serous envelope (see the black 

 layers in any of Figs. 70-S7). Thus, in Fig. 71, which is of this 

 stage, the previous fpiflu'lial reih of the coelom on both sides of the 

 connection are no longer distinct, and their place is taken l)y an 

 ill-defined reticular tissue which is intimately applied over the com- 

 pact epiblastic bridge. 



These new changes in tlie connection are very important, for they 

 are steps to the formation of the secondary sero-amniotic connection, 

 which will be explained in the following sections. 



It is necessary to say here a few words about the allantois. 'I'his 

 organ, which first appeared between the amnion and the serous en- 

 velope, on the right side of the embryo, about the time wlien the 

 timnion had closed itself, has in this stage come near the sero-amniotic 

 connection. As far as it has expanded itself, its vascular mesoblastic 

 tissue has fused, on its way, with the mesoblastic epithelium of the 

 serous envelope ; and so the mesoblastic net-work, ^vhich has spread 

 over the serous envelope, some distance beyond the connection is on 



1. Loe. cit. 



