88 



COLLEGE ZOOLOGY 



m 



Fig. Si. — Figures illustrating the cleavage of the holoblastic egg of Am- 

 phioxus, and the formation of germ layers. A-K, cleavage and formation of 

 the blastula. L— M, gastrulation. N, production of the mesoderm and 

 ccelomic cavities. O, ccelom further developed, ak, ectoderm; dh, primitive 

 alimentary canal; ik, entoderm; mk lt somatic layer of mesoderm; mk t , 

 splanchnic layer of mesoderm. (From Korschelt and Heider, after Hatschek.) 



N 



