19 THE ANIMAL PARASITES OF MAN 



worm [i.e., sexually complete] lies at the posterior end, is as a 

 rule of smaller size and different shape, it also frequently remains 

 sterile, as likewise happens in the next younger segments in a few 

 species ; otherwise, however, sooner or later the generative organs 

 develop in all the segments, mostly singly, sometimes in pairs ; 

 in the latter case they may be quite distinct from each other 

 or possess some parts in common. Most of the species combine 

 male and female genitalia in the same segment, only a few are 

 sexually distinct (Dicecocestus). In the hermaphrodite species one 

 male and one female sexual orifices are always present, and, in 

 addition, there may be a second female orifice, the mouth of the 

 uterus ; as a rule, however, this is lacking, and in one genus the 

 other sexual orifice, the opening of the vagina, is also absent. The 

 position of these orifices varies ; the cirrus and vagina usually 

 open into a common space on one lateral border or on a surface 

 of the segments ; the orifice of the uterus may be on the same 

 surface or on the opposite one. 



The surface on which the uterus opens is termed the VENTRAL 

 SURFACE ; if this orifice is absent, one must depend on the female 

 organs, particularly the ovary, which almost always approaches one 

 of the two surfaces ; the proximal surface is then called the ventral. 



The length of the Cestodes independently of their age depends 

 on the number and size of the segments, as well as on their 

 contraction ; the smallest species (Davainea proglottina) may measure 

 o\5 i'o mm. in length ; the largest may attain a length of 10 mj6., 

 and even more. 



ANATOMY OF THE CESTODES. 



' The entire superficial surface of the tapeworms is covered with 

 a fairly resistant and elastic cuticle, which also covers the suckers, 

 and is reflected inwardly at the sexual orifices ; in some species 

 fine hairs appear, either on the entire body or only in the region 

 of the neck, on the external surface of the cuticle, which exhibits 

 several indistinct layers. Close under the cuticle lies the external 

 layer of the parenchyma (basal membrane) and immediately after 

 the elements of the dermo-muscular tube. The matrix cells of the 

 cuticle are, as in the Trematodes, only on the other side of the peri- 

 pheral muscles in the external zone of the parenchyma ; they are 

 fusiform cells forming one or two layers, but are not arranged in 

 the manner of epithelial cells. They have fine branching pro- 

 cesses which run between the cuticular muscles, pass through the 



