1914] A New Cestode from Amia Calva L. 99 



The vas deferens passes forward from the sperm-reservoir 

 almost in the median line and dorsal to the uterus-sac, taking many 

 irregular coils in its course (Fig. 17). In older proglottides, however, 

 owing to the relatively enormous distension of the latter, it is pushed to 

 one side until all parts, excepting those close to the vesicula seminalis, 

 may eventually become obliterated. It seems to be crowded more often 

 to the right, doubtless because of its position in younger stages; at any 

 rate, the anastomotic reservoir formed at its posterior end by the vasa 

 efferentia lies more often to the left. Fig. 17 is an exception to this, as 

 it is a dorsal view. 



In ripe joints before it is pushed aside by the developing uterine 

 cavity, the vas deferens is tubular in shape, from 11 to 14 ;u in diameter 

 at its anterior end where it joins the vesicula seminalis, 17 to 25 /^ at its 

 middle and 22 to 35 /x at its posterior expansion, the latter being the 

 diameter of the sperm-cistern. Later when it becomes gorged with 

 sperms and the walls are, in consequence, thinner, the diameter varies 

 from 40 to 55/x. 



The wall of the vas deferens consists of a low epithelium in which, as 

 in the sperm-reservoir, no cell boundaries can be made out, supported 

 by a poorly-developed basement-membrane (Figs. 21, 23a and b). It is 

 thus a syncitium. In older proglottides, where the vas deferens con- 

 tains sperms, the epithelium is flattened out so that the nuclei appear 

 here and there along the duct as thickenings in an otherwise thin mem- 

 brane. In young, and, as yet, non-functioning vasa deferentia nuclei 

 from the outer layer of the aniagen remain close to the basement-mem- 

 brane, especially towards the vesicula seminalis, to form the myoblasts 

 of scattered and fine circular muscles (Fig. 23). 



The vesicula seminalis, which is morphologically an ex- 

 pansion of the vas deferens, is situated close to the dorsal body-wall, 

 immediately behind the cirrus-pouch (Fig. 17). It is ovate to spherical 

 in shape in mature proglottides, before it is flattened against the latter 

 by the gravid uterus-sac, with the more pointed end directed anteriorly, 

 while in younger (but ripe) joints it graduates less abruptly posteriorly, 

 that is, it is more broadly spindle-shaped. The wall has the same 

 structure as that of the vas deferens, excepting that the syncitial epithe- 

 lium is so much thinned out, especially when the organ is filled with 

 sperms, that the nuclei, which appear singly or in groups of two or three 

 and surrounded by small amounts of clear cytoplasm, seem to be applied 

 to the inside of the basement-membrane itself. Outside of the latter 

 there are to be seen numerous fine muscle-fibres, with their myoblastic 

 nuclei, coursing in general longitudinal and circular directions. These 

 are similar in structure to those surrounding the vas deferens. On 



