404 SUBGENUS CYSTOT^ENIA. 



A. Cystic Tape- Worms in which the Head arises within the 

 Embryonic Madder. 



Subgenus Cystotaenia, Leuckart. 



We regard the cystic tape-worms in this division as normal forms, 

 and give them the first place in our consideration, not only because 

 they include the majority of the species, but particularly because in 

 their mode of development they closely follow the typical process of 

 the other tape- worms. To justify our assertion we may refer to what 

 we have already (p. 339 et seq.) said about the development of the 

 bladder- worms. What we have said will suffice also as an introduction 

 to these worms and their peculiarities, so far as they are revealed in the 

 young stages. Apart from the nature of the bladder and its usually 

 very lymphatic contents, the presence of the above described recep- 

 tacle is especially deserving of attention. It forms, as is well known, 

 a muscular pouch, which surrounds the rudimentary head with more 

 or less independence, and also subsequently encloses most of the body 

 of the worm which gradually originates between the head and the 

 bladder. 



By the continuous growth of the former the receptacle becomes 

 ever larger with increasing age, but never loses its compact shape. 

 In consequence of this the worm inside draws 

 itself more tightly together 1 till the receptacle 

 can contain it no longer, and then it is gradually 

 protruded by the evagination of its basal portion. 

 This occurs most constantly and most strikingly 

 FIG. 235. Cysticercus in the Cysticercus fasciolaris from the liver of 



celluloscB with the head i T 



in the receptacle. ( x 2.) mice and rats, where the worm protrudes some- 

 times a finger's length from the bladder, and 

 becomes by solidification and segmentation so like an adult tape- 

 worm, that it has even lately been erroneously described as such 

 (Fig. 236). 



To the subgenus Cystotcenia we refer not only the species with 

 the ordinary single-headed bladder-worm (Cysticercus), but also the 

 Tcenia ccenurus, which, in its youthful state, is well known to be poly- 

 cephalous. This proceeding is amply justified by the development 

 and subsequent condition of the head. The resemblance between 

 Ccenurus and Echinococcus is only superficial, and by no means war- 



1 The opacity caused by the twistings of the body of the worm within the receptacle 

 aggravates the difficulty of investigation to such an extent that the earlier, and sometimes 

 even the modern (as in Davaine's work), descriptions and illustrations of the parts of 

 bladder in situ are with few exceptions useless. 



