458 



ZOOLOGY 



SECT. 



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

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

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



Fio. 373. Chaetopterus. Natural 

 size of a young specimen. A, an- 

 terior region of the body ; B, middle 

 region ; C, hinder region, c, peri- 

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

 great " wings " ; /, the first of the 

 three "fans"; m, mouth. (From 

 Benhani, after Pauceri.) 



FIG. 374. Seta; of various I'nlychicta. (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 seise representing 

 the two parts. The setae 

 are nearly always chitinous ; 

 in Euplirosyne they are cal- 

 cified. 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 

 of setae are present in 

 different parts of each 



Fio. 375. Section of the setigerous sac of an Oligo- 

 chsete. b\, setigerous sac ; 6 2 , supplementary follicle 

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

 longitudinal muscles of body-wall ; m, m. muscles 



It of the setigerous sac ; r.m, circular muscular layer 

 of.body-wall. (From Hatschek, after Vejdovsky.) 



parapodium of a single 

 worm, or in parapodia of 



