No. 2.] STRUCTURE OF TWO FISH TAPEWORMS. 363 



Retraction would be accomplished principally by the roots, 

 which, as has been seen, are attached to the proximal end of 

 the inner tube. The vas deferens for a short distance without 

 the cirrus sac is of the same size as the cirrus itself, and could 

 be drawn into the pouch, thus providing for the extension. 



Female Generative Organs. — The vaginal opening is .008 mm. 

 in diameter. About .005 mm. back of the opening, a sphincter 

 muscle is found, .008 mm. in thickness and hemispherical in 

 cross-section. The vagina then bends backward and inward, 

 passing under the middle of the cirrus sac. It is of nearly 

 equal size throughout, and is lined by ciliated epithelial cells. 

 Outside of this is a thin, circular muscle layer bounded by deli- 

 cate epithelium. The whole vagina, toward its distal extremity, 

 is surrounded by a very prominent layer of glandular cells, with 

 long processes extending toward the duct. The vagina follows 

 the median line of the proglottis, close to the ventral body mus- 

 cles. Its course continues straight until it passes under the 

 ovaries, where it forms a number of coils ; from there passing 

 to the posterior end of the proglottis, and opening into the ovi- 

 duct (at od., PI. XVI, Fig. 28). Kraemer ('92) wrongly states 

 that it opens into the ootype. 



The ovary is a bi-lobed organ, composed of two retort-shaped 

 parts, connected in the median line by a narrow portion, corre- 

 sponding to the neck of the retort (Fig, 28, c). Each half of 

 the ovary is covered by a delicate membrane, composed of a 

 single layer of cells. The ovary is closely packed with ova, 

 which are .01 mm. in diameter when they are ready to leave 

 the organ. The germinal vesicle is very large, measuring 

 .0075 mm. in the mature ova, with a prominent nucleolus 

 .005 mm. in diameter. The eggs which are found in the ute- 

 rus have a diameter of .02 mm. This last measurement agrees 

 with that of Kraemer, but it will be noticed that the immature 

 ova in this specimen seem to be nearly twice the size he 

 describes. This difference might be accounted for by his over- 

 looking the delicate protoplasmic mass, which forms the outer 

 portion of an ovum. The ova pass from the ovary into the 

 oocapt, which is .025 mm. long and .02 mm. in diameter. It 

 is lined by cubical epithelium, which is surrounded by a muscu- 



