CIKCULATION IN EUNICE SANOUINEA. 



251 



Fig. 123. 



rests upon the pharyngeal portion of the digestive tube, without, how- 

 ever, being adherent thereunto, and com- 

 municates posteriorly with a vascular 

 circle that surrounds the stomach and 

 receives the blood from the intestinal 

 parietes through two longitudinal trunks 

 (fig. 123, I) situated upon the dorsal 

 aspect of the alimentary tube. 



(655.) In its course towards the head, 

 the single dorsal vessel (l') } which is a 

 continuation of the two dorso-intestinal 

 veins (Z), receives several branches, some 

 derived from the digestive canal, others 

 proceeding from the muscles and integu- 

 ments of the neighbouring part of the 

 back. These last-named branches com- 

 municate with a slender cutaneous me- 

 dio-dorsal vessel that runs along the 

 entire length of the body and receives 

 from each segment numerous cutaneous' 

 ramusculi (a?). Lastly, the dorsal vessel 

 gives off from its anterior extremity 

 various branches to the cephalic segments, 

 as well as others which are directed out- 

 wards, as in the Terebella described here- 

 after ; but these, instead of supplying 

 branchial organs, take a backward course, 

 and are either distributed to the parts in 

 the vicinity of the pharynx, or their ra- 

 mifications anastomose with those of the 

 ventral vessel, immediately to be de- 

 scribed. 



(656.) The ventral vessel (fig. 123, q 1 ) 

 gives origin, opposite each segment, to a 

 pair of lateral branches ; but the confor- 

 mation of these branches, as well as the 

 functions to which they are destined, are 

 very different. Immediately after its 

 origin, each lateral branch becomes con- 

 siderably dilated and bends back sud- 

 denly upon itself, so as to resemble, when superficially examined, an 

 following: a a, the ventral surface of the segments of the body ; e e, the ventral oars, 

 or packets of bristles ; //, the ventral cirri, or feelers ; g, the anal cirri ; h, the anus ; 

 *, k k, the bases of the dorsal and ventral oars, with their surrounding muscles ; 

 1 1, the dorsal longitudinal muscular bands ; m m, the ventral longitudinal muscular 

 bands. 



Circulatory and respiratory appara- 

 tus of Eunice sanguined : a, b, c, the 

 antennae ; e, the first segment of the 

 body ; f, lateral appendages, or rudi- 

 mentary feet ; g, pharynx; g', mandibu- 

 lar muscles ; i, intestine ; I', vessel per- 

 forming the functions of an aortic or 

 systemic heart ; I, superior intestinal 

 vessels ; s, their lateral branches (or 

 branchial veins) ; g', ventral vessel ; 

 f, its lateral branches ; t', contractile 

 ampullae, performing the functions of 

 branchial hearts ; u, branchiae ; x, sub- 

 cutaneous vessels of the back. (After 

 Milne-Edwards.) 



