455] PSEUDOPHYLLIDEA FROM FISHES— COOPER 167 



aperture equal to its whole diameter into the vagina just at its juncture with 

 this vestibule. But since the vagina constantly constricts a second time to a 

 diameter of about 8^ before entering the latter, one gets the impression of the 

 receptaculmn seminis being a diverticulum of the oviduct rather than of the 

 vagina. Figure 108 of four consecutive sections of a transverse series, showing 

 the union of these ducts, wiU give a better idea, perhaps, of the nature of the 

 seminal receptacle. 



In mature proglottides the ovary (Fig. 90) is a bilobed structure situated in 

 the median line, close to the posterior border of the proglottis and iirimediately 

 ahead of tlie uterus-sac of the proglottis following, where the latter is much dis- 

 tended with eggs (Fig. 75). In toto mounts the lobes seem to be quite separate 

 from each other, but in sections the isthmus is easily made out. It occupies 

 the ventral half of tlie medulla while the -^dngs or lobes extend completely 

 across the space between the layers of longitudinal body muscles. The lobes 

 are about 0.27mm. long by 0.13 wide, while the isthmus is 0.06 to 0.08mm. in 

 anteroposterior diameter. These proportions are, however, much different 

 in much contracted strobilas or in proglottides in which the uterus-sac is dis- 

 tended with eggs. In both instances the ovary is very much flattened antero- 

 posteriorly and, in the latter case, aU but obliterated, as shown in Llihe's 

 figure 8 (1902:326). The ova from that portion of the isthmus where they 

 are ready to be passed on by the oocapt, are elliptical to oval in outhne in sec- 

 tions and measure on the average 18 by 10/x, their nuclei being about 9/i in 

 diameter. 



The oocapt, situated in the median line at the posterior border of the ovar- 

 ian isthmus, somewhat dorsally, is a spherical to ovoid muscular organ about 

 20a'. in diameter (Fig. 103). Immediately behind it the oviduct constricts 

 to a diameter of only 7 to lOpt and then passes on posteriorly and ventrally either 

 to the right or to the left, gradually enlarging until the above-mentioned vesti- 

 bule is reached, when the diameter is 25 to 30ju. The latter enlargement is 

 less of the nature of a direct continuation of the o\dduct than a more or less 

 separate thin-walled structure — the walls of the oviduct up to this point being 

 comparatively thick (Fig. 108) — into which the oviduct opens by a shghtly 

 elongated aperture. WTiile the wail of the first portion of the oviduct consists 

 of more or less cubica.1 ciliated cells with somicwhat indefinite boundaries — 

 ordinarily they stain very densely — that of the vestibule shows only a few 

 scattered nuclei protruding into the lumen. The ovaduct continues postero- 

 laterally and ventrally from one corner of the vestibule (that with which the 

 vagina is usually connected) as a tube quickly diminishing from 15 to lO/i in 

 diamicter and lined with a ciliated epithelium with prominent nuclei but no 

 distinct cell-boundaries. Close to the anterior wall of the uterus-sac of the 

 succeeding proglottis it turns upward sharply and at about the middle of the 

 dorsoventral diameter of the medulla takes on the vitelline duct. It then skirts 

 the uterus-sac, just mentioned, as it passes to the opposite side of the generative 

 space and slightly forward, to soon become surrounded by the shell-gland. 



