431] PSEUDOPHYLLIDEA FROM FISHES— COOPER 



143 



few circular and longitudinal muscle fibres. Distally the cuticular lining is 

 reduced to a minimiun. Thus the cirrus when protruded, usually for a short 

 distance only, is a comparatively weak structure with thin walls, but a diameter 

 at the base of from 30 to 35/x. It is also quite short since in no place in the 

 sections made was it found extended more than half way to the external opening 

 of the genital cloaca, but more often, as noted above, turned around in the duc- 

 tus hermaphroditicus towards the vaginal opening. Thus it is evidently 

 adapted to the fimction of simply conveying the spermatozoa to the latter 

 orifice in the act of self-impregnation rather than of acting as an intromittent 

 organ in cross-fertilization. The diameter of the retracted cirrus was given 

 by Linton (1890:730) as 0.008mm. 



The cirrus-sac is comparatively long and cylindrical and extends from the 

 inner boundary of the genital cloaca to the median frontal plane of the pro- 

 glottis. While its dorsal half is situated more at right angles to the surface, 

 its ventral half bends over in the transverse plane to the right or left to become 

 related to the coiled vas deferens in the manner described above. This deflec- 

 tion of its proximal end thus alternates irregularly with the latter, and is always 

 away from the uterus-sac. The maximum length and diameter in the latter 

 case in the dorsal half of the organ are 0.500 and 0.145mm., respectively. As 

 shown in figure 88, and as noted by Linton, the walls are very thick, leaving 

 only a comparatively narrow cavity to accommodate the cirrus; they are com- 

 posed of a very powerfvil inner layer of circular muscles surrounded by a thin 

 layer of longitudinal fibres which do not have any points of attachment to the 

 body-wall, so far as could be determined. The space surrounding the ejacula- 

 tory duct and cirrus proper accommodates the fine and quite long retractor 

 fibres and a small amount of parenchymatous tissue. The retractors are not, 

 however, as large or numerous as in the previous species of the genus in which 

 the cirrus is better developed. 



The vagina, which opens close behind the cirrus and usually somewhat 

 towards the same side to which the latter is deflected, begins with a bulb-like 

 sphincter, quite like that described and figured by Linton (1898:436) for his 

 Dibothrium laciniatum, dOy. in length by about 90 in maximum diameter. The 

 walls of this structure, 40/x in thickness, are composed of two layers of muscle 

 fibres of equal thickness: an outer of loose circular, and an inner of somewhat 

 radially arranged fibres. The whole organ would thus appear to be adapted 

 to the pumping of the sperms into the vagina. The latter proceeds ventrally 

 with a diameter of about 25/x, after enlarging considerably immediately behind 

 the bulb. It is surrounded by circular fibres only. At the level of the ventral 

 end of the cirrus-sac it joins the oviduct. 



The ovary, which has an average width of 0.45mm., is irregularly branched 

 in mature proglottides, much compressed anteroposteriorly by the numerous 

 coils of the uterine tube, and often displaced from the median hne by the latter 

 and the spacious uterus-sac. Furthermore, while the isthmus, itself irregular in 

 shape and hence somewhat difficult to distinguish from the rest of the organ, 

 *'lies next the irmer side of the lateral [ventral] muscular wall," the wings 



