STRUCTURE OF ANNELIDA AND ENTOZOA. Ill 



tufts axe arranged regularly on the several segments, and the 

 animal can swim by the motion that it gives them ; besides 

 these, it has a kind of bristle-shaped appendage, that seems 



Fig. 52. NEREIS. 



like a rudimentary leg, which assists it in crawling. Eut 

 there are others of these marine- worms, that form a tubular 

 shell, in which they reside during the greatest part of their 

 lives; and in these the gills, if disposed along the body, 

 would have been removed from the access of water ; they are 

 therefore arranged round the head, often forming (as in the 

 fSerpulce, fig. 145) tufts of great brilliancy and elegance. 



105. Eelow the Annelida are other worm-like tribes of yet 

 greater simplicity of conformation, but still presenting the 

 same general plan of structure. Of one of these the common 

 Leech may be taken as an example; of another, the Tape- 



Fig. 53. TAPE-WORM. 



worm (fig. 53). This last belongs to a group termed ENTOZOA, 

 from the circumstance that they inhabit the bodies of other 

 animals. They are remarkable for the very low development 

 of their digestive apparatus, their nourishment being appa- 



