GASTRULATION OF DESMOGNATHUS FUSCA. 



well flown on the yolk mass and appearing as a cleft between 

 the small cells which have grown down about the larger one-. 

 This early cleft in all of my specmiens appears to be not entirely 

 formed by invagination. In later stages, however, there is good 

 \idence of ingrowth especially from the small cells of the upper 

 lip. In ,i numU-r i -pecimens of this stage, the rounded yolk 

 cells which were in or ne.ir the segmentation cavity are more or 

 less artificially rro\\drd to^-ther, probably due to the loss of 

 fluid bet \\eeii them in tin- pa--a<^e through the alcohols, so that 

 no clear idea wa- obtained of their position-. It is probable 

 tli.it about the time of iM-irulation then- i- a con-iderable change 

 of po-iiion of <rll- at tin- animal pole of the egg, tin- relU may 





. 

 ' 





FlG. 3 1 In- 1 



ui.li, 



lin-ii -ImiiiV.' \li.it 



in tin- .! 



11 ilirii)Ji -I l.it< : u 11- 



' ' tti-.l IK 'III tin- -III- 



:ln- .rll- i- ailili'il. X25- 



ha\e a looser arrangement, tlu-rr ma\- even b- con-id. -ral.K- 



ana- brt \\rell thrill o. i'll|'ied b> tlllid. exidclirc of which ina\ 

 In- seen in ci-rtain li\ii 1'lu- I"-- "f thi> lluid b\- fixation 



Causes tlu- o>lla|>-i- of the thin roof and the croudin^ to- t -tln-r 

 .f iln- c.-ll- at the animal pi-!r ! . IIo\\r\i-r. in many 



-li-litl> later including both earlier specimens and those 



oill\ recently oblaiiud. 1 iieiitatioli ca\it\ - em- to ha\e 



been lauel\- li.-t and -till later than this, new -pace- between the 

 yolk cell- make their appearance and communic.il.- directly with 



