360 



EMBRYOLOGY 



side by a broad space. The ventral and dorsal parts of the 

 trunk-plate now grow out more and more on the sides, and 



Fig. loS.— .4 to F, stages of development of Sipunculus nudus (after Hatschkk). 

 J,bla8tiil;i; W.nastrula; C to K, other stages, in which the development of the head- 

 and trunk-platea takes place; F, embryo during hatching; a, anus; II, blasto- 

 pore ; dr, glandular appendage of the fore-gut; cct, ectoderm; cut, entoderm ; ka, 

 head amniotic cavity; m, mouth; mc», mesoderm; n, nephridium; ra, trunk 

 amniotic cavity; rj), trunk-plate; .s, pharynx; se, serosa; so, somatic, »p, splanch- 

 nic, layer of the mesoderm ; "', ciliated band. The ectoderm is finely and the ento- 

 derm coarsely punctate ; the mesoderm is cross-hatched. 



