XOO S. GOTO. 



nucleus whicli mostly occupies a central position is very small and 

 contains a single or a few small nucleoli. In this genus as well as in 

 Axine and Microcotyle the cells in question are mostly present around 

 the terminal half of the vas deferens and are entirely absent near the 

 testes. As I have said above, these cells remained to me an enigma 

 for a long time ; judging from their appearance I was tempted to at- 

 tribute to them a secretory function. Fortunately, however, the study 

 of Hexacotyle in the latter part of my studies solved for me the 

 enigma. In some sections of Hexacotyle acuta, one of which I have re- 

 produced in fig. 5, PI. XII, I could distinctly trace the efferent ducts 

 of numerous cells around the vas deferens having a coarsely granular 

 protoplasm. These cells seemed to be destitute of any membrane, 

 were of an irregularly polygonal shape, and their nuclei contained 

 each a single or sometimes a few nucleoli. They are therefore ,very 

 similar to the cells already described in Microcotyle, except in the 



t 



coarseness of their protoplasmic granules. Not only could the efferent 

 ducts be distinctly traced up to the thick membrane of the vas deferens, 

 but a granular substance exactly similar in appearance to the contents 

 of the cells above described (except in staining more deeply) could be 

 observed on the inner surface of the membrane, forming numerous 

 prismatic columns. Each of the-se columns has doubtless been formed 

 by the secretion of a single cell, which is therefore the prostate gland. 

 After this observation every one would admit that the peculiar cells 

 around the vas deferens in Axine, Microcotyle, and Monocotyle are of the 

 same nature, since they occupy similar positions and closely resemble 

 one another in their appearance as well as in their reaction towards 

 staining fluids. I have not been able to observe the efferent ducts in 

 the genera just mentioned ; but this is, I believe, owing to the fact that 

 the glandular cells were in the state of rest when the animal was killed. 

 At least in the case of the shell-glands afterwards to be described, the 



