458 



ZOOLOGY 



SECT. 



of parapodia or merely a greater or smaller number of setae. Para- 

 podia are lateral hollow processes of the body- wall bearing a number 

 of bristles or setae. Frequently the parapodium is divided horizon- 



FIG. 373. Chaetopterus. Natural 

 size of a young specimen. A, an- 

 terior region of the body ; B, middle 

 region ; C, hinder region, o, peri- 

 stomial cirri ; d, " sucker " ; e, the 

 great " wings " ; /, the first of the 

 three " fans " ; m, mouth. (From 

 Benham, after Panceri.) 



FIG. 374. Setae of various Polychaeta. (From 

 Claparede.) 



tally into two distinct lobes or branches a dorsal which is termed 

 the notopodium, and a ventral which is termed the neuropodium. 



Even when this is not the 

 case there may be two 

 bundles of setae representing 

 the two parts. The setae 

 are nearly always chitinous ; 

 in Euphrosyne they are cal- 

 cined. They are always 

 solid, except in Euphrosyne, 

 entire, or divided into a 

 number of joints. In shape 

 (Fig. 374) they vary greatly 

 in different groups ; often 

 several very distinct forms 



FIG. 375. Section of the setigerous sac of an Oligo- ^ Se ^ 8e are Present in 



cha3te. &!, setigerous sac; 6 2 , supplementary follicle different parts of each 

 with seta ; e, deric epithelium (epidermis) ; Im. -, . r . -. 



longitudinal muscles of body-wall ; m, m. muscles parapodium of a Single 

 of the setigerous sac ; r.m, circular muscular layer ^Ji ~f 



of body-wall. (From Hatschek, after Vejdovsky.) Worm, Or in parapodia Ot 



