No. 2.] STRUCTURE OF TWO FISH TAPEWORMS. 353 



upward, passing into the ootype about the center of that space. 

 Its course is never exactly the same in different proglottids. 

 Throughout its course the oviduct is supplied with gland-like 

 cells, enclosed in a single-layered epithelium and lined by a 

 layer of ciliated epithelial cells (PI. XVI, Fig. 6). The oviduct 

 is easily distinguished from other ducts in this region by reason 

 of its greater size, darker staining, and more regular course 

 (PI. XVI, Fig. 16, od^. The diameter remains about the same 

 throughout. The ova, as they pass down the oviduct, are fer- 

 tilized by the spermatozoa from the vagina before they reach 

 the ootype. 



The ootype is a direct continuation of the oviduct (PI. XVI, 

 Fig. 1 2, ot. and od.). It possesses a circular muscle layer, and for 

 its entire length is surrounded by the shell gland. Its position 

 is about the center of the interovarial space. It receives the 

 common vitellarian duct at its beginning, and the secretion of 

 the surrounding shell gland throughout its course, resembling 

 precisely the ootype of P. tondosa d^sx^ P . filicollis (Kraemer, '92). 

 It has exactly the same structure, with the addition of a mus- 

 cular coat, as has the oviduct, even to being provided with the 

 gland cells, which are embedded in the shell gland (PI. XVI, 

 Fig. 12). Its entire length is only ,06 mm., and its diameter 

 .015 mm. Its walls are no thicker than those of the oviduct, 

 the cubical epithelial cells not being so large, and this decrease 

 being equalized by the muscle layer. The ootype opens directly 

 into the uterus, there being here no intermediate duct, such as 

 is commonly described in other species. It is possible that one 

 of the coils of the thick-walled portion of the vagina has been 

 mistaken in some cases, at least, for the duct leading to the 

 uterus. There can be no doubt in P. mnbloplitis that the uterus 

 extends directly forward from the ootype, yet many sections 

 seem to show such a duct, which, on careful reconstruction, 

 always proves to be nothing more than one of the coils of the 

 vagina. The walls of the uterus are very delicate, of a fibrous 

 texture, and the lumen at its beginning is .05 mm. in diameter. 

 It runs directly anteriad to just in front of the ovary, where it 

 turns back and proceeds in a dorso-posterior direction to near 

 the posterior end of the proglottis. It then makes a turn toward 



