III. CESTODA 



253 



formation of numerous daughter bladders produces marked tumors in the liver 

 of man and domestic animals, before the formation of scolices begins. In the 

 interior of each daughter vesicle appear a number of brood vesicles, each of 

 ,-hich produces numbers of scolices, so that from a single six-hooked embryo 



\v 



thousands of scolices can arise (fig. 232). In contrast to this extreme case are 

 others which connect with the development of Botliriocephalus, in which the 

 cvsticercus is replaced by a cysticercoid (fig. 231). Here there is no infiltration 

 and the scolex is closely enclosed by an envelope comparable to the bladder wall. 

 In several cysticercoids a caudal appendage recalls the cercaria. 



The development of a tapeworm was earlier believed to be a complicated 

 alternation of generations; the bladder to be a stage which by budding produced 

 scolices; the scolex, in turn, a stage which by terminal budding produced the 

 sexual animals, the proglottids, and the tapeworm itodf a chain of individuals, 

 a strobila. This view, so easy to learn, contains' two errors. The bladder is 

 not an independent generation, but only the hinder end of the scolex. The 

 tapeworm is not a colony, but a single animal; the proglottids are not individuals, 

 but specialized parts of a whole. This view is confirmed by a comparison with 

 other forms. The Caryophyllaeidae (fig. 233) are single bodies, the anterior end 



FIG. 231. FIG. 232. 



FIG. 231. Invaginated and extended cysticercoid from a slug (Arioii) (from 

 Hatschek) . 



FIG. 2^2.T(rnia echinococcus (after Leuckart). Right sexually mature; left a part 

 of an echinococcus with two brood capsules and their scolices. 



elongate and taking the place of the scolex, while the broader hinder part con- 

 tains a single hermaphroditic apparatus. In the Ligulidae the body is still 

 unjointed, but has increased in length and contains numerous sets of sexual 

 organs. This duplication of the reproductive apparatus explains the appear- 

 ance of proglottids. In this multiplication of the gonads, which is connected 

 with the entoparasitic life and the necessity of increasing the fertility, lies the 

 reason for the division into proglottids. 



Family i. CARYOPHYLL.EID.E. No suckers, simple sexual apparatus, scolex 

 and proglottis not differentiated. Distinguished from trematodes by absence 

 of digestive tract. Larval stages in invertebrates, adults nearly always in fishes. 

 Caryophylheus (fig. 233); Arrhigetcs in annelids (Sa-mtris'). Family 2. LIGULID^C. 

 No suckers; numerous sexual organs, but no proglottids. The immature 

 stages in fishes, the adults in birds. Linn-la* Family 3. TETRARHYXCHID.*:. 

 With scolex and proglottids, the head with four protrusible hooked probosces 



