;^4(; UTIJOTA : ON THE SEKO-AMXTOTrO rONXECTTOX, 



tlic right .side directly traceable to that of the allantois (Figs. 5. 6, 

 and l)n). 



-0. Itt'jihiceiiieiit of Cells in t]\c Scrn-Jmfiiotic ('oniicctioN. 



T liave mentioned in Section 2, that as the head-fold grows hack- 

 wards, the epiblastic delta of it« posterior edge is c(mstantly, though 

 only partially, being removed by the insinuation of the extra-enibryouic 

 coelomic cavities of the two sides ; and that the remnant of the delta is 

 prolonged backwards as the ' Amnionnaht ' or the sero-amniotic con- 

 nection. This process of insinuation prevails from the very beginning 

 of the formation of the delta, and is continued after the amniotic cavity 

 is closed. The mesoblastic net- work, having reached both sides of the 

 connection, begins to pierce across the remnant epiblastic cell-bridge, 

 so tliat at lenoth the mesoblastic cells of one side meet with those of 

 the opposite side, as we see in Figs. 72 and 74. 



F'rom the sixth day the epiblastic bridge is broken uj) here and 

 there, beginning with the anterior part of the connection (Figs. 71, 72, 

 73, 74, and Figs. ()-7). In the posterior part of the connection, where 

 the amniotic cavity has finally closed, remains of the epiblastic cell- 

 mass, which there was the last to form, are found for a long time as 

 irregular patches, as in sections (Figs. 76-7 (S and Fig. 8). Sometimes, 

 the epiblastic cell-mass appears in sections as isolated ])atches iml)edded 

 in the mesoblastic tissue, as in Fig. 7<S, but by tracing them in other 

 secti(His they are found to l^jecome continuous with the (qjil)last either 

 of the amnion or of the serous envelope, lîy tlie ninth to tlie tenth 

 day of the incubation, the epiblastic bridge has been (•ompletely 

 replaced, along the entire length of the connection, by mesoblastic 

 cells (Figs. 4.S-50). 



The epiblast of the amnion and of the serons enveIo])e are now 

 eiilii'clv discoiitiimoiis. lint the amnion and tlie serous envelope, 



