350 BENEDICT. [Vol. XVI. 



resembles that of P. ambloplitis, the chief difference being in 

 the more delicate structure, and the lesser number of coils of 

 the vas deferens within the pouch. 



Female Generative Organs. — The opening of -the vagina is 

 directly anterior to the male opening and is of variable size. 

 The duct passes directly inwards for about .05 mm., and then 

 enlarges to twice the size of the opening. The lumen remains 

 constant in diameter for about .35 mm., during which distance 

 the tube curves anteriorly, and then posteriorly again, taking a 

 course which varies from a nearly straight one to a semicircle, 

 but which always ends at about the same level as the opening. 

 Throughout the region just described the vagina possesses an 

 extraordinarily developed sphincter muscle, which is .03 mm. 

 in greatest thickness. This muscle is very compact and must 

 possess great strength. It is by far the most powerful sphincter 

 about the vagina yet described in any cestode. The absence 

 of any hooks and the shape of the cirrus render this structure 

 an important one in most of the Proteocephali. This sphinc- 

 ter makes the terminal region of the vagina nearly as large 

 and prominent in sections as the cirrus pouch (PI. XVI, Fig. 

 18, va). 



On emerging from the sphincter muscle the cavity of the 

 vagina enlarges suddenly, forming an elongated chamber with 

 convoluted walls, which is directly downward and backward, 

 narrowing as it nears the median body line (PI. XVI, Fig. 9, 

 va). From the opening to the end of this enlargement the 

 vagina is lined by a continuation of the body cuticula, which 

 becomes very thin in the chamber, and there bears delicate 

 cilia (PI. XVI, Fig. 18). Enclosing the sphincter is a layer of 

 loose glandular cells resembling those of the cirrus (PI, XVI, 

 Fig. 19, ms. and cl.gl.). Outside of these cells is a delicate 

 epithelial layer (PI. XVI, Fig. 19, <?/.). The chamber with con- 

 voluted walls is undoubtedly for receiving at the time of copu- 

 lation a mass of spermatozoa, which may be passed on as the 

 capacity of the remaining vaginal duct will permit. It is impos- 

 sible to trace the transition from the lining cuticula to the free 

 epithelial layer which lines that portion of the vagina extending 

 from the chamber to the oviduct. This portion of the vagina 



