470 



ZOOLOGY 



SECT. 



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

 prostomium in such a case bears eyes and tentacles and contains 



Fie. Mils. Seta? of various Polyrlwta. (From Chiparede.) 



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

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



rrn 



Fii; 3i>;i. Section of tlic setigerous sac of an Oligochsete. bj, setigerous sac ; Z>g, supplementary 

 follicle with seta ; e, deric epithelium (epidermis); ?m, longitudinal muscles of body-wall ; 

 ~m, ,K. muscles of the setigcrous 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 palpi. 



