360 



EMBRYOLOGY 



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

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



Fig. 158.—^ to F, stages of development of Sipuncidus nudus (after Hatschek). 

 A, blastula ; B, gastrula ; C to E, other stages, in which the development of the head- 

 and trunk-plates takes place ; F, embryo during hatching ; a, anus ; hi, blasto- 

 pore ; dr, glandular appendage of the fore-gut; ect, ectoderm; ent, entoderm ; fca, 

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

 amniotic cavity; rp, trunk-plate; s, pharynx; se, serosa; so, somatic, sp, splanch- 

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

 derm coarsely punctate ; the mesoderm is cross-hatched. 



