GASTRULATIOX OF DESMOGNATHUS FU5CA. 



and these may represent some of the early small cells which have 

 migrated about the yolk. Some of the cells near the opening 

 of the blastopore have grown in dorsally and the ventral lip 

 is also to some degree made up of small cells, some of which 

 may be followed into the floor of the archenteron (Fig. 5). 



In later gastrula stages as the enteron becomes more and more 

 marked, there may IM- noticed a considerable ingrowth of cells, 

 -pecially from the dor-al lip, in ><>me -pecimeiis can-ing this 

 free portion of the roof to !,<< -ome rolled as Hr.uier 1 found to be 

 the i ase in the < '.ymnophiona ! 



I- i ;i.ni tli; n <-inlir\ 



iu-1 \ in. -In. \vinu tin- l.i! 



i tin- 



\i a time \\lu-n the 1. la-lop,, re i- reduced t<> a \ cr\ -mall hole 

 and HIM before medullar> fold- are formed, the ca\il\ ha- come 

 to lie lar^e and e\lell-i\e. Fig. ~ i- from a CTOSS Section of -ueh 

 a Stage. In it the me-obla-t ha- not j>enet rated \er\ far \eiitrally 

 e-pecially in tlu- mon- cejihali. ;. Later than thi-, \\ hen the 



neural plale has liev^un to close, w- find that a- \et in the head 

 end the me-ol.la-i does QOl extend much farther but. in the 

 caudal region, it ha- ]>enetrated between the ectobla-t and the 



\. Mr.ui.-i. .! Ki-nntin- I!,T Knt\vicki-hinj;sK<'sclii' !it<- und 



-I. r liyinniiphii'iirii." /.<><>!. J<ilirb. Anal. Abl.. Bd. X.. i 



