232 



THE VITAL FUiNCTIONS. 



nial, allied to the Leech, and already noticed in 

 the account of the mechanical functions of this 



tribe :* where a is the anterior and p the posterior 

 extremity of the animal, the dorsal vessel occu- 

 pying the middle straight line between the two 

 lateral vessels, and the direction of the stream 

 in each being indicated by the adjacent arrows. 

 Fig. 348 is a lower view of the Erpobdella, show- 

 ing the numerous ramifications of the abdominal 

 vessel ; the lesser branches encircling the nervous 

 ganglia, and accompanying the principal nervous 

 filaments which proceed from them ; while the 

 lateral vessels are seen pursuing a slightly serpen- 

 tine course. t 



In these tribes, the respiratory portion of the cir- 

 culation consists merely of small vessels branching 

 out from the lateral vessels, and returning to them, 



* Vol. i. p. 243, where a delineation of this anitoal was given, 

 Fig. 130. 



t In the communicating branches, which pass clown transversely 

 from the dorsal to the lateral or abdominal vessels,, the blood gene- 

 rally moves downwards. It must be confessed, however, that there 

 exists great discrepancy in the accounts given by different natu- 

 ralists of the course of the blood in the vessels of the Annelida. 

 Much confusion has been produced by the ambiguous designations 



