TREMATODA 221 



enclosed in a muscular CIRRUS SAC, or more rarely passes directly into 

 the genital pore. The cirrus, which is the thick muscular terminal 

 portion of the vas deferens, can be everted and protruded from the 

 cirrus sac and serves as an organ of copulation. The walls of the 

 muscular portion of the tube (the cirrus) are attached to the walls of 

 the cirrus sac, and hence when the sac contracts the cirrus cannot 

 be protruded except by evagination of its lumen. Opening into the 

 middle portion of the vas deferens, and as a rule enclosed in the cirrus 

 sac, is found a mass of unicellular glands (prostate), the vesicula 

 seminalis (which is likewise within, or may also be outside the sac) 

 being the dilated first portion of the vas. 



The female genitalia (fig. 1 26) consist of an ovary, usually situated 

 in front of the testes, the form of which varies according to the 

 species, the usually double vitellaria, the ducts and a number of 

 auxiliary organs ; the short oviduct directed towards the centre 

 arises from the ovary, and is connected in the median line with 

 the excretory duct of the vitelline glands. These grape-like glands 

 possess longitudinal excretory ducts, which assume a transverse 

 direction behind the ovary, unite together at the median line and 

 form a single duct, often dilated into a vitelline receptacle, that unites 

 with the oviduct. Near this point, moreover, there frequently opens 

 a canal (Laurer's canal) which begins on the dorsal surface, and 

 on the inner end of which a vesicle filled with sperm (receptaculum 

 seminis) usually occurs (fig. 126). Moreover, there are also numerous 

 radial unicellular glands (shell glands) at or beyond the point of 

 junction of the oviduct, vitelline ducts and Laurer's canal. In this 

 portion of the duct (ootype), which is usually dilated, the ovarian 

 cells are fertilized, surrounded with yolk cells and shell material, 

 and as ova with shells they pass into the uterus (a direct continua- 

 tion of the oviduct), which, with its many convolutions, occupies a 

 larger or smaller portion of the central field, and runs either direct 

 to the genital pore or, forming convolutions, first runs posteriorly 

 and then bends forward (descending and ascending limbs). In both 

 cases the terminal part lies beside the cirrus pouch and discharges 

 beside the male orifice either on the surface of the body or into a 

 genital atrium. The terminal portion of the uterus, which is often 

 of a particular structure, serves as a vagina (METRATERM). 



The cirrus sac may include (i) the genital atrium (i.e., the 

 common sinus, into which the vas deferens and vagina may open), 

 or (2) a variable extent of the vas from cirrus to seminal vesicle. Thus 

 the latter may be outside the sac. In the absence of a sac, the genital 

 sinus may be surrounded by a pseudo-sucker, as in Heterophyes (in 

 some cases the ventral sucker itself, from its close proximity to the 

 genital pore, serves as an accessory copulatory organ). In other cases 



