38 ON A NEW SPECIES OF ENTEROPNEUSTA, 



limiting membrane of the collar cord to form the capillary net on 

 on its dorsal surface, and branches also pass downwards in the 

 boundary membrane laterally to the perihaemal spaces and come 

 into direct connection with the capillary net of the inner wall of 

 the collar. Very few vessels leave the ventral side of the dorsal 

 vessel in this species, and the capillary net of the inner wall of 

 the collar thus appears to stand mainly in connection with vessels 

 derived from the dorsal side of the dorsal vessel, in common with 

 the capillary net of the collar cord. 



Ventral Vess'l of Trunk : The ventral vessel is related exactly 

 as in Pt. minnta. It does not extend so far posteriorly as the 

 dorsal, but disappears at the point of origin of the keel-shaped 

 process of the gut. 



Lateral Vessels : The lateral vessels are essentially similar to 

 those of the described species. In the branchial region they 

 occupy the usual position just below the submedian lines (fig. 20, 

 llv.). Then when the lateral septa appear, they run in these (fig. 

 22, llv.). Towards the ends of the septa the vessels gradually 

 pass downwards towards the point of attachment of the septa to 

 the -gut, and then behind the termination of the septa they con- 

 tinue as free vessels lying in the interior of the now greatly 

 reduced genital wings (fig. 24, llv.) and which finally about the 

 middle of the hepatic region pass over into the gut capillaries. 

 In this part of their course the vessels possess, as in the other 

 species, circular muscle fibres in their walls, and also from the 

 latter there radiate outwards fine fibres (fig. 24, llv.), prolja])ly 

 functioning as expansors. 



Gill Vessels : My observations on this very complicated set of 

 vessels confirm, so far as they go, those of Spengel. The afferent 

 gill vessels arising from the dorsal vessel vary according as the 

 dorsal vessel occupies the whole of the mesentery or only its 

 dorsal half. In the former case the afferent vessels pass off* 

 directly from the ventral side of the dorsal vessel; in the latter 

 they diverge outwards and downwards from its ventral side, the 

 mesentery being apparently absent at this point. The afferent 



