DEVELOPMENT OF A CH IM.FJROID. 



2/5 



in the suppression of these vacuolar cleavage spaces would re- 

 sult in a homqgeneous and nucleated subgerminal zone. In- 

 deed, in the present material the vacuoles do disappear from the 

 subgerminal zone (Figs. 10 and 1 1), although they appear as be- 

 fore at the side of the germinal area, and below it, separating 

 masses of the yolk. Note also in this connection the presence 



" 



0%, 



v***' up V_<7 



-' .- -, 1 , , \-^ s^^z-s S-,: 



1^6 



-* 5 - 1 



FIG. 9. Early blastula. 'Vacuoles are shown, continuous in arrangement with 

 cleavage spaces. .SC. Early segmentation cavity. 



of nuclei in the marginal yolk masses thus separated as below 

 the marks * L and *, two points in the section, Fig. I I. And in 

 another stage, Fig. IO, 1 it will be seen how far peripherad these 

 nuclei can be traced, c. g., at the points I., II., III., IV. and 

 V. as far peripherad, in other words, as this region of the 

 egg has been sectioned. It follows accordingly that the yolk 

 mass is separated from the germinal region by no means as 

 abruptly in Chiincera as in the allied sharks. For in CJiimcera, 



ni s<& i 



FIG. jo. Early gastrula. Sagittal section A. Archenteron. BP. Blastopore. 

 SC. Segmentation cavity. I-V. Nuclei lying outside of the germinal area. 



as we have seen, vacuoles which in some cases at least represent 

 intercellular spaces pass deep into the yolk region, in the form 

 of more or less vertical fissures. Moreover, again unlike sharks, 

 the yolk nuclei which surround the margin of the germinal area 



1 On one side of the present section nuclei I. and II. occur in the eighth section, 

 and III. and IV. in the seventh and sixth sections respectively ; on the opposite side 

 nucleus V. occurs in the fourth section. 



