CESTODA. 



333 



several (Ccenurus) hollow buds, which are developed from the walls 

 and project into the interior of the vesicle (fig. 268, c). The 

 armature of the tape- worm head (suckers and double circle of hooks) 

 is formed on the inside and at the bottom of this invagination of 

 the wall of the vesicle (fig. 268, d). When these hollow buds are 

 evaginated so as to form external appendages of the vesicle, they 

 present the form and armature of the Cestode head, as well as a 

 more or less developed neck, which presents even at this stage traces 

 of segments (fig. 268, e). In some cases (Echinococcus) the irregularly 

 shaped maternal vesicle produces from its internal walls one or two 

 generations* of secondary vesicles which project into it; and the 

 Cestode heads originate in special small brood-capsules 

 on ther? *r>condary vesicles (fig. 269, a). In such 

 cases the number of tape-worms which arise from 

 one embryo is naturally enormous, and the parent 

 vesicle may reach a very considerable size, being some- 

 times as large as a man's head. In consequence of 

 this enormous growth the vesicles frequently obtain 

 an irregular shape ; while on the other hand, the tape- 

 worms which are developed from them remain very 

 .small, and carry, as a rule, only one ripe proglottis 

 (fig. 370). 



So long as the tape-worm head (scolex) remains 

 attached to the body of the bladder-worm and in the 

 host of the latter, it never develops into a sexually 

 mature tape-worm ; although in many cases it grows 

 to a considerable length (Cysticercus fasciolaris of the 

 house-mouse). The bladder- worm must enter the 

 alimentary canal of another animal before the head 

 {scolex) can, after separation from the body of the 

 bladder-worm, develop into the sexually mature tape- 

 worm. This transportation is effected passively, the new host eating 

 the flesh or organs of the animal infected with Cysticerci. The tape- 

 worms, therefore, are principally found in the Carnivora, the Insecti- 

 vora, and the Omnivora, which receive the bladder-worms in the flesh 

 of the animals on which they feed. The vesicles are digested in the 

 stomach, and the cestode head becomes free as a scolex. The latter is 

 protected from the too intense action of the gastric juice by its 

 calcareous concretions, and at once enters the small intestine, fastens 



* In Cysticerci (0. longicollis, tenuicolli?} also sterile daughter vesicles are 

 sometimes budded off. 



m 



FIG. 270. Taenia 

 Echinococcus 

 (after R. Leuc- 

 kart), magni- 

 fied 12 to 15 

 times. 



