l6 THE ANIMAL PARASITES OF MAN 



although he no longer considered the bladder-worms as hydropic- 

 ally degenerated tapeworms, he still regarded them as taeni^e 

 that had strayed. This change of opinion was partly due to an 

 important work of the Prague zoologist, v. Stein (1853), who was able 

 to examine the development of a small bladder-worm in the larvae 

 of the well-known meal-worm (Tenebrio molitor), and to demonstrate 

 that, as Goeze had already proved in the case of Cysticercus fasciolaris 

 of mice, first the caudal vesicle is formed and then the scolex, 

 whereas Siebold believed that in bladder-worms the posterior end of 

 the scolex was formed first, and that this posterior end underwent a 

 secondary hydropic degeneration. 



In opposition to v. Siebold, Kuchenmeister successfully proved 

 the necessity of the bladder-worm stage by rearing tapeworms 

 in dogs from the Cysticercus tenuicollis of domestic mammals 

 and from the Ccenurus cerebralis of sheep. He, and simulta- 

 neously several other investigators independently, succeeded, with 

 material provided by Kuchenmeister, in rearing the Ccenurus 

 cerebralis in sheep from the oncospheres of the Tcenia ccenurus 

 of the dog (1854). R. Leuckart obtained similar results in mice 

 by feeding them with the mature proglottides of the Tcenia 

 crassicollis of cats (1854). 



Kuchenmeister also repeatedly reared the Tcenia solium of 

 man from the Cysticercus cellulosce of pigs (1855), and from the 

 embryos of this parasite P. J. van Beneden succeeded in obtain- 

 ing the same Cysticercus in the pig (1854). As Kuchenmeister 

 had taught to distinguish the Tcenia mediocanellata, known to 

 Goeze as Tcenia saginata, amongst the large taeniae of man (1851), 

 it was not long before R. Leuckart (1862) succeeded in rearing 

 the cysticercus of the hookless tapeworm in the ox. It is 

 particularly to this last-named investigator that helminthology is 

 indebted more than to any other author. He followed the 

 gradual metamorphosis from oncospheres to cystic worms in all its 

 details. 



In view of all the researches that were made and which are too 

 numerous to mention individually, the idea that bladder-worms are 

 abnormal or only incidental forms had to be abandoned. Every- 

 thing points to the fact that in all cestodes the development is 

 divided between two kinds of animals ; in one the host, the adult 

 tapeworm is found ; while in the other, the intermediary host, we 

 find some form or other of an intermediate stage (cysticercus in 

 the broadest sense). The practical application of this knowledge 

 is self-evident. If no infected pork or beef is partaken of, no 



