444 



ZOOLOGY 



SECT. 



and the anus and proctodsem are formed by a fresh invagination 

 in the original position of its posterior end, while another in- 

 vagination of the ectoderm further forwards gives rise to the 



ctnt 



oes 



ov 



i,^ ,7 P , , ^vis, a hermaphrodite tubicolous Polydia-t. Lateral view of entire 

 . i m.m neph anterior nephndium ; In: branehi* ; a. iwophagus ; op. opemilum with 



embryos in its anterior ; oc. ova ; sp. sperms ; st . stomach. (After Claparede.) 



mouth and stomodseum. The embryo then passes into the 



Ti vck os'phci 'c ,s tage . 



The arrangement of the cilia on the surface of the Trochosphere 

 varies in different Polychoeta. Sometimes, though rarely, the prse- 



