GASTRULATION OF DESMOGNATHUS FUSCA. ~ 



surrounding the archenteron are as smoothly pressed back from 

 the lumen as though some definite substance occupied the large 

 cavity. 



The variations from time to time of the cavities within the 

 egg are quite striking. The variations in extent of the segmenta- 

 tion cavity, its reduction and disappearance in some specimens 

 at least, the developmen: ally in the later stages of clefts 



bet \vrcn cells, the growth in extent of the archenteron and its 

 reduttion by the time the nervous >\ -tern is developed; all of 

 ihe-e changes may be dependent upon the large yolk ma-- and 

 the peculiarities of environment. . If this last be a factor of 

 importance in the < a\ ity change- within the eggs, then we miuht 

 expect to find, as ue <1". -Mine variation in individual- of the 

 -ana- n-lati\< "f d, \ , |, .pmeiit , for females with e-i;- or 



yoim- are found in place- that are from wet to almo-t dry at 

 different seasons <>r during the -aim- -m inner. 



- MI < ',l \i k \l ( A INI i.i -f INS. 



1. The -mall-^ranuled, -mall cell- < !' animal pole v^n-w about 



the larger with greater or less filling in i the segmentation cavity. 



2. The tell- <>l the allimal pole be.., ill. reduced to olle la\ er. 

 .v The In -I indication 't ; K a-t rulat i< m .ip|>ear- in the VCgel Ltive 



liemi-pheie .it a re^i"M bet \\i-en the -mall cell- \\hich ha\e ^i"\\'n 

 do\\ n and the \<>lk t ell-. 



4. There i- an in^n >wtli < -I" -mall cell-, from the d<>r-al lip 

 e-peciall\ . 



5. The e.ul\ -e^meiitatit'ii ca\it\ a- -uch |imbabl\- dm-- lid 

 bt O >me i"ined tn the in\ agination. 



6. The later an hem en. r, is fi .in led parth by in\ agination and 

 ]iai'tl\ b\ -eparatii m betu !!-. 



7. The ca\it\ o!" the anhenten.n i- a|iparenll\ made up of 

 in\a'j.inated cell-. \nlk .ell- and included under either ..lie or 

 both of these, some oi the -mall cell- which ha\e migrated from 

 the re^i'H "I the animal pule. 



8. The -mall cell- at the animal pole form ect<>bla-t. 



<). The -mall cell- .it the animal pule at lea-t -mile of which 

 an- under the SUrl Us form me-obla-t and probabK' -ome 



eiitt '1 'la-t . 



