kuchenmeister's expeeiment. 335 



found. This transference occurred, of course, when the first hosts 

 were eaten by the second. In a great many instances he was even 

 able to follow the metamorphoses step by step, and thus really to 

 prove that in these marine Cestodes the already supposed division of 

 the developmental history into two epochs or stages, spent in different 

 hosts, was an actual fact. 



The observations of van Beneden would have made more im- 

 pression if the illustrious zoologist had been able to trace the 

 development back to the six-hooked embryo. The existence of this 

 embryo was unfortunately but little attended to, and the formation 

 of the cysticercoid forms was connected simply with a stage in which 

 the young worm (Scolex, Eud.) had essentially the organization of the 

 subsequently formed head. 



And further, van Beneden agreed with v. Siebold in thinking that 

 the cysticercoid stage of the Cestodes was not absolutely necessary 

 but rather accidental, and tbat it only occurred when the germ was 

 not directly transferred to the alimentary canal. ^ In this way the 

 migrations described by van Beneden lost a large part of their 

 significance. They were characterised more as accidental than as 

 normal processes.^ 



Our knowledge of the development of the Cestodes was thus still 

 far from satisfactory. It was Klichenmeister again who led us in the 

 right direction by a fortunate experiment. 



In August 1853 Klichenmeister^ fed a wether wi'.h the ripe pro- 

 glottides of a tape- worm, which had been reared in the intestine 

 of a dog from the familiar bladder-worm of the sheep (Ccenurus). 

 Eighteen days after he found in the brain of the now diseased wether 

 a number of small round bladders, which he identified with young 

 Cosnuri, and which were in fact perfectly identical with the bladders 

 which Haubner had described as their first stage. 



Thus it was proved that the six-hooked Cestode embryo, if trans- 

 ferred to the alimentary canal of an animal, wanders from the latter, 

 and settling in other organs, often far removed, becomes by metamor- 

 phosis a bladder-worm. 



^ " Je crois que le ph&nombne de I'involvation {i.e., the formation of a cysticercoid 

 Tetrarhynchus) ne se montre que ohez les Scolex qui arrivent dans les replis p^riton^aux, 

 comme aussi les Scolex de T6uia ne deviennent Cysticerques que dans des conditions 

 analogues." — Loc. cit, p. 82. 



* Afterwards, in his great work on the intestinal worms, which appeared in 18.58, and 

 therefore several years after the researches of Klichenmeister, v. Siebold, Wagener, and 

 myself, he abandoned his earlier theory, and correctly explained the life-history and de- 

 velopment of the Cestodes. It is, therefore, hardly consistrnt with historical fact for van 

 Beneden to claim, as he does in a recent work (" Die Schmarotzer des Thierreiches," p. 

 119, 1876), that he was the first to disclose the true meaning of Cestode development. 



' GUnaburg's Zeitschr. f. Uin. Vortrdge, p. 448, 1853. 



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