BY JAS. P. HILL. 33 



dorsal vessel i-etains its lumen to near the posterior end of the 

 body. 



As Spengel has found in Pi. minuta, the place of the ventral 

 vessel is taken by the keel-shaped process of the gut epithelium. 

 As in Pt. ndnutd, a very delicate musculature is found on the gut 

 in this region, and as in that species a distinct sphincter derived 

 from the circular musculature exists round the anus. 



Vascular Sy ste m. — Dorsal vessel : In the post-branchial 

 region the dorsal vessel is related essentially as in Pt. minuta. 

 It can be traced as a vessel with a distinct lumen to near the 

 posterior end of the hodj; it appears, however, to end as a solid 

 structure at its extreme posterior end just as in Pt. minuta. In 

 the branchial region the dorsal vessel may occupy the whole of 

 the mesentery or only its dorsal portion. Between the perihsemal 

 spaces the dorsal vessel usually occupies the whole extent of the 

 partition wall, but just as in Pt. minuta it may only occupy the 

 dorsal half of it, and the ventral part of the wall may then either 

 persist as a low wall of partition below the vessel, or it may 

 disappear entirely and place the two perihsemal spaces in com- 

 munication. 



At the anterior end of the perihaemal spaces, the dorsal vessel 

 opens, as in the described species, into a lacuna (figs. 11, 12, 14, 

 cl.) betvreen the organs in the proboscis neck and which stands in 

 connection with the central blood space of the proboscis by a 

 narrow cleft. From the lacuna there passes away dorsally a vessel 

 (fig. 10, oav.), the afferent skin vessel, which Spengel regards as 

 carrying blood to the capillary net of the proboscis. Where two 

 proboscis canals are present it passes between them (fig. 10); 

 where there is only one canal, along one side of that. It then 

 passes into the limiting membrane and runs in that anteriorly for 

 a short distance, finally dividing as in the described species into 

 two branches which divide up again to form the capillary net of 

 the proboscis. 



Proboscis glomerulus : The glomerulus of this species essentially 

 resembles that of Pt. minuta. It covers the anterior ends of the 

 c 



