ORGANIZATION OF CERATOCEPHALE OSAWAI. 



/ d,v. 



r. ni., rete mirabile ; 



B 



P.1UV. 



V.V. 



d. v.. Dorsal vessel ; 



"'. v., Ventral vessel ; 



p. a., Proboscidial artery ; 



/. t\, Proboscidial vein ; 



p.n.w., Proboscidial vascular 



net-work. 



off laterally some small vessels which go into the first three feet of the 

 same side. The vascular passage forming the inferior edge of the rete 

 and running along the dorso-lateral sides of the ventral nerve-cord, may be 

 spoken of as its efferent vessels, to which I shall soon return 



In the first segment and in front of the first pair of the afferent vessels, 

 the dorsal vessel gives origin to a pair of proboscidial arteries, one on each 

 side. Turning backwards, the proboscidial arteries (j> a.) run along the 

 dorso-lateral side of the proboscis, show between them a transverse anasto- 

 mosis in the third segment and soon after this break up each into a vascular 

 network (/>. n. zu.) on the sides of the proboscidial wall. Each of the net- 

 works gives off from its anterior parts a vein, the proboscidial vein (_/>. v.), 

 which proceeds ventrally to a point in the midventral line where the two 

 from both sides unite into one in the median line. The unpaired probosci- 

 dial vein, formed by this union, freely traverses the body-cavity downwards 

 till finally it joins the anteriormost end of the ventral vessel (f. v ) in the 

 fourth segment. In its course the unpaired vein is much twisted about, a 

 condition which disappears as the evagination of the proboscis causes it to 

 straighten out. 



Ihe anterior end of the dorsal vessel, after giving off the proboscidial 

 arteries, enters into the head ; there it sinks beneath the brain and splits 

 into three branches, one median and two lateral, all which supply blood to 

 the head and the tentacular cirri 



From the parts just mentioned the blood is carried off backwards by 

 four small veins in all, there being two of them on each side On both 

 sides, the two unite into one at a position antero-lateral to the infra-ceso- 

 phageal ganglion. The pair of the veins thus formed pass posteriorly, each 



