ORGANIZATION OF CERATOCEPHALE OS AW A I. 



241 



into two branches, an outer, and an inner. The former is the superior 

 parapodial artery {sup. p. a.), supplying blood to the upper ramus of the 

 foot beloneinsr to the same segment The latter pursues its course into 

 the dorsal body-wall and forms the subcutaneous artery (sc. a., figs, j and 

 2), running transversely along the posterior margin of the segment and 

 giving off the subcutaneous capillaries which are mainly anteriorly 

 directed. 



The close-meshed subcutaneous capillaries of the back and of the 

 parapodia (figs 2 and 3) can be beautifully made out on specimens 

 hardened in alcohol, then treated with a weak solution of eosine and 

 clarified with clove-oil The parts mentioned, but especially the delicately 

 constructed ligulae, constitute without doubt the chief seat of respiration in 

 the worm 



The ventrally situated, lateral arteries stand in direct connection with 

 the dorsal vessel by means of vessels, the dorso-ventral vessels (dv. v. fig. 

 1), of which there is a pair to each of the segments. The)' spring from 

 the lateral artery at a point some distance away from the origin of the 

 latter from the ventral vessel but somewhat nearer to it than to the origin 

 of the inferior parapodial artery. The two dorso-ventral vessels forming a 

 pair, as they ascend, clasp between them the intestinal canal and on the 

 dorsal side of this, unite into one which soon opens into the dorsal vessel on 

 die lower side The point of this junction is on the same level as the 

 origin of the lateral veins and lies near the anterior margin of the segment. 

 In their course along the sides of the intestine, the dorso-ventral vessels 

 stand in connection with the capillaries of the intestinal wall Thus, the 

 blood ascending the vessels in question goes in part directly into the dorsal 

 vessel and in part into the intestinal wall From the latter the blood 

 seems to be led into the dorsal vessel by means of a few (four or five to 

 a segment) small vessels extending between that vessel and the intestine. 



As before indicated, the above described vascular arrangement shows 

 deviations in the anterior parts of the worm body. Firstly, as regards the 

 modification in the five successive segments following the 4th, i. e , in the 

 segments 5th — 9th, it may be said to stand more or less in relation with the 



