Fig 167 Presumptive organ-forming areas in the uncleaved egg and durmg cleav- 

 age and blastulation in Amphioxus. (Original diagram based upon data obtained from 

 Conklin '32 '33.) (A) Uncleaved egg. (B) Eight-cell stage. (C) Early blastula m 

 (D) Late blastula in section. (E) Late blastula, external view from side. 



section. 



(F) Late blastula, external, vegetal pole view. (G) Late blastula, external, dorso- 

 posterior view. The localization of cytoplasmic materials in Styela partita is similar to 

 that of Amphioxus. Observe that the pointed end of the arrow defines the future cephalic 

 end of the embryo. The position of the polar body denotes the antero-ventral area, while 

 the position of the notochordal and neural plate material represents the antero-dorsal 

 region. The "tail end" of the arrow is the postero-ventral area of the embryo. 



353 



