24 ANIMAL PARASITES. 



host lias been devoured by a cat, and they themselves thus 

 transplanted to their proper soil, they may cast off' their degene- 

 rated segments, return to the normal form of T. crassicollis, 

 and arrive at sexual maturity. By a similar degeneration, young 

 individuals of the Tenia plicata, when they stray from the intes- 

 tine into the abdominal cavity of the horse, become deformed 

 into Cysticercus fistularis} I am also convinced that the vesicu- 

 lar worms, referred by Rudolphi to the genus Anthocephalus, 

 are nothing but Bothriocephali or Tetrarhynchi which have strayed 

 in their migrations and become degenerated." 



Subsequently also (' Zeitschr. fur wiss. Zool.,' 1850, p. 220), 

 in the revision of the Tetrarhynchi, Von Siebold repeatedly says, 

 "that the cystic worms are really only (strayed) tape-worms, 

 engaged in their migration, which have remained undeveloped 

 and become dropsically degenerated, but which, on getting into 

 favorable circumstances (i. e., into the intestine of an animal), 

 become perfectly healthy and mature, and are even destined to 

 wait for this act of swallowing." At last he even breaks out 

 into the words, " I have reason to believe that, with the excep- 

 tion of the Cysticercus fasciolaris, and perhaps the C. crispus, no 

 other cestode- nurse which has degenerated into a cystic worm 

 can so far return to its normal condition, from its dropsical state, 

 as to become fit for the production of sexual individuals. This is 

 shown by the fact that the high degree of dropsical swelling causes 

 such a great extension of the body, that, even from this, we may 

 conclude that these tape-worms can no longer acquire the faculty of 

 producing sexual individuals by the formation of segments, and the 

 ceslode-nurses, which have become degenerated into Cysticerci, 

 perish without descendants, as is proved by the empty Cysticercus- 

 cysts with their remains." This proposition was refuted by 

 experiments in the administration of cystic worms of all kinds, 

 and the principal evidence upon which Von Siebold supported 

 his opinion was destroyed, but the proposition itself was still 

 upheld by him, as we shall soon see. 



The production of the cystic worms, according to Von 

 Siebold and Dujardin, does not take place directly from the 

 embryos, but in this way, — that tape-worms already developed, 



1 It is only possible to place together the T. plicata and Cystic, fistularis, and thus 

 regard them as belonging to one and the same species, if we regard the mode of life of 

 the animal infested, as of no value at all in the discrimination of species amongst the 

 Tcenice ('Leucka:t, Die Blasenbandwiirmer,' p. 38). 



