365] PSEUDOPHYLLIDEA FROM FISHES— COOPER 77 



tral and transverse diameters are, respectively, 85 to 90/i and 60 to 80ju. In 

 the anterior and posterior ends of the proglottis — they are not continuous 

 from segment to segment but separated by the aggregations of sagittal and 

 transverse muscles mentioned above as forming more or less complete septa — 

 they form a single layer situated in the medulla in the median frontal plane, 

 but are widely separated in the middle of the proglottis by the central genital 

 organs and ducts, especially the uterus-sac. Their number ranges from 80 

 to 120 for each proglottis. While the wall of the testis consists of a very thin 

 membrane from which nuclei protrude inwardly, the contents are such as to 

 show the process of spermatogenesis quite clearly. The vas deferens forms 

 a circular mass of coils, 0.25 to 0.30mm. in diameter, applied like a cap to 

 the dorsal side of the developing uterus-sac and thus close to the inner end 

 of the cirrus-sac. When the uterus becomes gorged with eggs it is pushed aside 

 somewhat but still retains similar relations with one of the pouches of the for- 

 mer, located in the direction of the genital cloaca (Fig. 68). In the mass of 

 coils the duct is usually distended with spermatozoa to a diameter of 40/i. 

 It gradually narrows down to a diameter of 15/i before entering the cirrus- 

 sac, before which there is, however, no seminal vesicle. But within the pouch 

 the vas deferens enlarges to form a large seminal vesicle, which with a diameter 

 of from 50 to 60jLi takes only a few coils before passing on as the cirrus proper 

 from which it is sharply separated (Fig. 101). The cirrus is a slender tube from 

 0.17 to 0.22mm. in length within the pouch and from 15ju in diameter nearest 

 the seminal vesicle to 8/x at its opening. It is lined with a thin cuticula which 

 is circularly cleft in its proximal one-third but almost smooth for the rest of 

 its length, nowhere, however, showing anything in the nature of an armament. 

 The cirrus-sac (Fig. 101) is an elongated flask-shaped structure with a maximum 

 diameter proximally of 1 lOju and distally of 40^i, and a length of 0.35mm-. The 

 neck of the organ usually shows a couple of dorsoventral curves, while about 

 20^1 of its distal end protrudes into the hermaphroditic duct. Its walls are 

 comparatively thin and composed of an inner layer of circular muscles and 

 an outer weaker and much less compact layer of longitudinal fibres. Apart 

 from the seminal vesicle which occupies almost the whole of the proximal en- 

 larged portion and the narrow cirrus, the contents consist of only a limited 

 amount of parenchymatous tissue and a very few feeble retractor muscles. 

 The whole structure of the cirrus-sac is in fact such as to suggest that the 

 function is that of an organ for the explusion of spermatozoa rather than for 

 the emission of a copulatory organ; altho a few muscles passing from the 

 body wall around the cloaca to the anterior part of the neck of the sac (Figs. 

 100, 101) would seem to indicate that a small portion at least of the cirrus is 

 protruded, perhaps during self-fertilization. 



Altho the vagina opens into the hermaphroditic duct directly ahead of 

 the cirrus, it almost im.mediately curv'cs around the distal portion of the 

 cirrus -sac to the antero ventral side of the latter which it follows closely towards 

 the median Une. Close to the wall of the inner end of the cirrus-sac, however,, 

 it crosses the distal coils of the vas deferens towards the dorsal sufrace and 



