STUDIES OX THE ECTOPAßASITIC TREMA IODES OF JAPAX. (J<) 



tion with the genital titriuin. In Hexacodjle the homologue of the 

 connective-tissue penis of such genera as Tristonuun, EpihdeUa, and 

 Monocotijle is present in the form of a conical papilla at the top of 

 which opens the vas deferens, as will be explained under ' General 

 Considerations.' 



Glandula puostatica — So far as I know, the prostate gland has 

 hitherto been described only in Trist oimnii among the ectoparasitic 

 Trematodes ; but according to my observations it is present in all the 

 genera described in this paper. Only in Oclocotijlc I have not been 

 able to demonstrate it owins: to scantiness of the material and its bad 

 preservation. Even early in the course of my present studies my 

 attention was drawn to cells of a peculiar appearance around the vas 

 deferens, wliich were very luilike those of the mesenchyma ; but tlieir 

 nature long remained to me a problem. In Axine (PI. YIII, tig. 1) 

 and Microcotijk (?1. Ill, fig. 10 ; PI. Y, fig. 6) they always occupy 

 the mediîui portion of the body, and in some species this portion is al- 

 most wholly occupied by tliese cells to the exclusion of all others (PI. 

 Ill, fig. 10). They are of a rounded or more frequently of a polygo- 

 nal outline, with a finely granular, deeply staining protoplasm destitute 

 of any distinct external membrane. In Microcotijh the nucleus is 

 usually very large and conttiins one or more nucleoli ; but in Axiuc it 

 is smaller (PI. VIII, fig. 1). In Monocotijle also, peculiar cells can 

 always be observed in the mesenchyma around the vas deferens 

 (PI. XYIII, fig. 2, /^ro.s. (jl.) which always f )rm a group very con- 

 spicuous in sections. The individual cells are in this case provided 

 with a membrane of its own, and are more or less vacuolated, the 

 granular protoplasm farming simply a thin layer just inside the cell- 

 membrane, or radiating in threads from the nucleus towards the peri- 

 phery, or sometimes distributed uniformly but thinly through the cell- 

 body. The form of the cells is either polygonal or globular, and the 



