444 



ZOOLOGY 



SECT. 



and the anus and proctodsem are formed by a fresh imagination 

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

 vagination of the ectoderm further forwards gives rise to the 



FIG. 34(i. Spirorbis Isevis, a hermaphrodite tubicolous Polychaet. Lateral view of entire 

 animal, ant. ncph. anterior nephridium ; br. branchise ; as. oesophagus ; op. operculum with 

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



mouth and stomodseum. The embryo then passes into t 

 Trochosphere stage. 



The arrangement of the cilia on the surface of the Trochosphe 

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



: 



