468 



ZOOLOGY 



usually very similar throughout the length of the body ; but in 

 the Cryptocephala (Figs. 366, 367, 373) there may be two or even 

 more regions distinguishable from one another by the form of 

 the segments and of their appendages. In the Oligochseta there is 

 a thickened zone, the cliteUum, comprising sometimes only one 

 segment, sometimes a number. Each segment,- with certain 

 exceptions to be noted presently, bears either a pair of parapodia 

 or merely a greater or smaller number of seta?. Parapodia are 

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



Fig. 3tS0. — A Serpulid (Vertnilia cuespitosa). Lateral view of animal removed from its tube. 

 abd. abdomen ; br. branchia; ; op. operculum ; th. thorax. 



bristles or setae. Frequently the parapodium is divided horizon- 

 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 the two parts. The setae are nearly always 

 chitinous; in Euphrosyne they are calcified. They are always 

 solid, except in Ewphrosyivi, entire, or divided into a number of 

 joints. In shape (Fig. 368) they vary greatly in different groups ; 

 often several very distinct forms of seta? are present in different 



