470 



ZOOLOGY 



SECT. 



peristomium , forms in many Polychseta a very distinct head ; the 

 prostomium in such a case bears eyes and tentacles and contains 



FIG. 308. Set* of various Polychpeta. (From Claparede.) 



the cerebral ganglion ; on the peristomium is the opening of the 

 mouth, and from it also arise the peristomial tentacles. A 



Frr, 3Gf>. Section of the setigerous sac of an OligocliEete. fcj, setigcrous sac ; ?>.>> supplementary 

 follicle with seta ; e, cleric epithelium (epidermis) ; Im, longitudinal muscles of body-wall ; 

 5/1, m, muscles of the setigerous sac; r.m, circular muscular layer of body-wall. (From 

 Hatschek, after Vejdovsky.) 



ventral pair of prostomial tentacles, somewhat thicker than the 

 rest, are sometimes to be distinguished, and are termed the patyi. 



