The publication of Küchenmeister’s works induced v. Siebold to undertake similar experiments (1852 and 1853), which were partly published by his pupil Lewald in 1852. But the positive results obtained hardly changed Siebold’s opinion, for although he no longer considered the bladder-worms as hydropically degenerated tapeworms, he still regarded them as tæniæ that had strayed. The change of opinion was partly due to an important work of the Prague zoologist, v. Stein (1853). He was able to examine the development of a small bladder-worm in the larvæ 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, Küchenmeister successfully proved the necessity of the bladder-worm stage by rearing tapeworms in dogs from the _Cysticercus tenuicollis_ of domestic mammals and from the _Cœnurus cerebralis_ of sheep. He, and simultaneously several other investigators independently, succeeded, with material provided by Küchenmeister, in rearing the _Cœnurus cerebralis_ in sheep from the oncospheres of the _Tænia cœnurus_ of the dog (1854). R. Leuckart obtained similar results in mice by feeding them with the mature proglottides of the _Tænia crassicollis_ of cats (1854). Küchenmeister also repeatedly reared the _Tænia solium_ of man from the _Cysticercus cellulosæ_ of pigs (1855), and from the embryos of this parasite P. J. van Beneden succeeded in obtaining the same _Cysticercus_ in the pig (1854). As Küchenmeister distinguished the _Tænia mediocanellata_, known to Goeze as _Tænia saginata_, amongst the large tæniæ of man (1851), so 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. Everything pointed 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 intermediate 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 ingested, no tapeworm can be acquired, and also the rearing of cysticerci in the human body is prevented by avoiding the introduction of the eggs of tapeworms.