47<i 



ZOOLOGY 



jwistomi am, forms in many Polychseta a very distinct head; the 

 prostomium in such a case bears eyes and tentacles and contains 



Fig. 30S. — Setrti of various Polychasta. (From Cliiparecle.) 



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

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



Frc. 369.— Section of the setigerous sac of an Oligochtete. 6], setigerous sac ; h^^ supplementary 

 follicle with seta: c, deric epithelium (epidermis); ^7?i, longitudinal muscles of body-wall; 

 ?ji, m, muscles of the setigerous sac; r.in, 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^a^pi. 



