90 ANIMAL PAEASITES. 



organs of the Cestodea are formed. It may be recognised par- 

 ticularly well in Bothriocephalus rectangularis of the barbel, 

 when the parts are pressed together by means of a compressor 

 between two glass plates. 



The structure of the T&nice with which we are particularly 

 occupied here is best recognised when some of their anterior 

 segments, exhibiting the first foundations of sexual organs 

 are pressed between two glass plates, and the whole is held 

 up to the light for examination. Posteriorly and laterally, 

 in the median line, lie the two wijig-like clear germigenes ; above 

 them is the dense testicular tube, and between the two the first 

 formation of the uterus, (a perpendicular clear canal, particularly 

 dilated above). The vitellogenes lie in the form of opaque bands 

 partly on the outside of the longitudinal canals. All these 

 parts are very firmly imbedded in the parenchyma; the 

 vagina and seminal ducts scarcely exhibit a double muscular 

 wall. As already remarked, they possess a beaker-shaped sexual 

 cloaca closely surrounded by muscles, in which the cirrhus and 

 vagina open in common ; this occurs in most Tanice, but not in 

 all (for example, not in T. elliptica}. 



At the bottom of this space, which is furnished with tumid 

 margins, we see above the distinct orifice for the male sexual 

 apparatus, and below it the smaller vaginal aperture into which 

 the male organ, which is protruded from the first-mentioned 

 orifice, in the form of a small papilla or of a longer cylindrical 

 filament (cirrhus s. lemniscus], enters during copulation. The 

 male organ is pyriform, and exhibits internally transverse and 

 longitudinal muscular fibres, and externally a structureless epi- 

 dermis. The penis lies in a peculiar pouch, which may be called 

 the cirrhus-pouch (sac of the penis). In its interior runs the vas 

 deferens, the inner membrane of which turns outwards during the 

 protrusion of the penis, and then gives the exterior of the penis 

 an appearance as if it were beset with fine retroverted hooks. 



In the vagina no internal, direct connection of the male and 

 female sexual organs takes place, and this is also denied by Van 

 Benedeu in the Trematoda. At its entrance into the lower part 

 of the uterus it becomes enlarged into a true seminal receptacle, 

 and the combination of the structures necessary for the formation 

 of the ova undoubtedly takes place in the vicinity of this point at 

 the lower part of the uterus. 



The large germigenes lie right and left, close to the descending 



