BY JAMES P. HILL. 737 



occupies a median position, and then it may be formed in three 

 ways : (1) from the union of both dorsal proboscis pockets into a 

 single proboscis canal ; (2) from the left pocket alone forming the 

 canal; (3) from the right pocket alone. Then again the pore 

 may be single and on the right side of the median line, or median 

 and double. 



The notochord (Eicheldarm) of this species does not essentially 

 differ from that of Pt. minuta as described by 8pengel. It 

 possesses a distinct lumen extending to within a short distance 

 of the apex; and opening into the lumen are numerous secretory 

 cells. 



An interesting feature is presented by the ventral wall of the 

 heart-bladder. It is infolded into the cavity of the bladder 

 forming a tube free anteriorly and communicating with the 

 central blood space by a narrow longitudinal slit. This is 

 regarded as a special modification to insure the better performance 

 of the propelling function of the ventral wall of the heart-bladder. 



The ner\ e cord of the collar essentially resembles that of Pt. 

 minuta. As in that species a central lumen is absent. The 

 " cord hollows " are, however, not so numerous as in that species. 

 Two lateral longitudinal rows of such hollows are present, while 

 smaller less regularly arranged hollows may be present mesially. 



The "roots" vary in number from 1-4. The gonads are much 

 branched, and in the genital region proper there are in connection 

 with each genital pore at least six lesser branches. 



As in the majority of the species of the genus two ciliated 

 bands are present in the intestine. They extend forward for a 

 considerable distance into the genital region proper. 



The most interesting point in connection with the vascular 

 system is the presence of a well-marked vessel which passes in 

 the " chondroid " tissue occupying the space between the anterior 

 portion of the "keel" of the proboscis skeleton and the posterior 

 portion of the " end plate," and connects the two eiferent proboscis 

 vessels. 



This paper, with illustrations, will appear in the next Part of 

 the Proceedings. 



