THE CESTOIDEA 95 



from Dujardin, Leuckart, and others ; but the matter remained one 

 of mere speculation till 1851, when Kiichenmeister, a medical man 

 of Zittau, commenced a series of experiments in feeding suitable 

 animals with bladder-worms. Thus, he mixed a known number of 

 Cyst, pisiformis from the rabbit's omentum with the food of dogs, 

 and he obtained after a time a number of specimens of Taenia 

 serrata from their intestines. Similarly, he demonstrated that 

 C. cellulosae from the muscles of the pig gives rise to Taenia solium 

 when swallowed by man ; and that the small heads removed from 

 Coenurus cerebralis, which lives in the brain of sheep, develop, when 

 fed to a dog, into Taenia coenurus. He then caused the ripe pro- 

 glottids of this worm to be swallowed by a sheep, which a month 

 later had an attack of " staggers." It was killed, and fifteen small 

 coenuri were found in its brain. 



These and other experiments placed the relations of the " cystic 

 worm " to the " tapeworm " on a firm basis, and were soon followed 

 by others, undertaken by von Siebold (43), Leuckart, van Beneden, 

 whereby it was proved beyond doubt that the bladder-worm or hyda- 

 tid is an essential stage in the development of those tapeworms, 

 from the eggs of which they arise. Further, it became evident 

 that two different animals, or " hosts," are necessary for the com- 

 pletion of the life -cycle ; the bladder- worm occurring in some 

 definite intermediate host, which forms the prey or food of the final 

 host, in which the bladder-worm develops into the tapeworm. 1 It 

 was recognised that " cystic worms " occur in the muscle, connective 

 tissue, and various viscera, other than the alimentary canal (of 

 herbivorous animals as a rule) ; and that the adult tapeworms 

 always live in the alimentary canal (of carnivorous animals as 

 a rule). 



But still other problems remained for solution, especially that 

 which Steenstrup's famous theory of " alternation of generations " 

 had suggested, and this and other matters are dealt with at the 

 end of this chapter, as some of these details are still matters of 

 controversy. 



Among the more important writers on the classification and descrip- 

 tion of new genera and species, the following may be mentioned : 2 Redi 

 (1687-1705), Pallas (1781), Goeze (1782), Kudolphi, Zeder, Dujardin 

 (1845), E. Blanchard (1847), P. J. van Beneden (1849), Diesing, Krabbe, 

 Linton, Stiles, Raillet. The anatomy of various forms has received par- 

 ticular attention at the hands of Blanchard, Wagener, von Siebold, and 



1 In a few instances there is, however, no change of hosts, but merely a change of 

 organs in one and the same host. The best known case is that, H. murina, elucidated 

 by Grassi, where the cysticercoid occurs in the villi of the intestinal wall, the strobila 

 in the cavity of the same intestine. Von Linstow has found the larvae of Tetra- 

 rhynchus longicollis in the same fish as the adult, and so for Triaenophorus nodulosus. 



2 For a complete historical account and bibliography, see Bronn's Thierreichs, 

 Warmer, by Max Braun. 



