4(i8 



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 i'rom one another by the form of 

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

 a thickened zone, tlie cliteUam, comprising sometimes only one 

 segment, sometimes a number. Each segment, with certain 

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

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

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



. 3(i(.;.--A Serpulid (Verinilia ccespitos;0. Lateral view of aiiinial removed from its tube. 

 abd. abdomen ; br. branchiw ; op. operculum ; tk. thorax. 



bristles or seta\ Frequently the parapodium is divided horizon- 

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

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

 Even when this is not the case there may be tvvo bundles of setai 

 representing the the two parts. The seta' are nearly always 

 chitinmis ; in Euphrosyni they ai'c calcified. They are always 

 solid, except in Ewplirosyiv:, entire, or divided into a number of 

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

 often several very distinct forms of set;e arc present in different 



