IV. i INITIAL STRUCTURE OF THE GERM 



233 



hemisphere composed almost entirely of the clear substance, and 

 a vegetative hemisphere, the anterior portion of which includes 

 grey yolk and nothing else, the posterior portion the yellow 

 protoplasm together with a little yolk near the vegetative pole. 



The cleavage furrows separate these substances from one 

 another in a perfectly definite way (Fig. 143). The first is 



FIG. 143. Cleavage of the egg of Cynthia 2)(trtita. (After Conklin.) 



A. 8 cells, from the left side. 



B. 8 cells, from above. The yellow crescent (thickly clotted) is 

 limited to the posterior dorsal cells : the animal cells are clear, the grey 

 yolk (sparsely dotted) is found in the dorsal cells, both anterior and 

 posterior. 



c. 16 cells, from the dorsal side. 



D. 74 cells, dorsal view, showing the division of the 4 neural plate- 

 cells (n.p), and 4 chorda cells (ch.~). There are 10 endoderm cells (e), 

 6 muscle-cells (m.s.), 8 posterior (p.m.ch.') and 2 anterior (a.m.ch.) 

 mesenchyme cells. 



