294 VERMIFORM ARTICULATA. CLASS OP ANNELIDA. 



Crustacea ( 852). In the lowest Articulata, however, no 

 dorsal vessel, or impelling organ of any kind, can be discovered ; 

 and the circulating system consists merely of a network of 

 capillary vessels, occasionally merging into larger trunks ; the 

 blood being propelled through it by the continual movements of 

 the body itself, which act upon it in somewhat the same manner 

 that our own changes in position do upon our venous circulation 

 (ANIM. PHYSIOL. 279). 



904. This group may be regarded as especially represented 

 by the class ANNELIDA ; which contains, with the Leech and 

 Earthworm, a great number of marine animals less gene- 

 rally known. In the ENTOZOA, we find the characters of the 

 Articulated series in their lowest state of development. And in 

 the ROTIFERA, we meet with peculiarities of form so great, that 

 the affinity of the minute animals it contains to the preceding 

 classes, is by no means apparent without a careful examination. 



CLASS OF ANNELIDA. 



905. The Annelida may be characterised as possessing an 

 elongated body, marked by transverse lines that divide it into 

 numerous segments : and usually furnished with a series of loco- 

 motive appendages in the form of bristles, sometimes implanted 

 on fleshy tubercles ; but not with articulated members. They 

 have a complete apparatus for circulation and respiration ; and 



FIG. 621 NEREIS. 



the ventral chain of nervous ganglia may always be distinguished. 

 Of the appendages which often combine the functions of loco- 



