ANIMAL PARASITES. 23 



influence of this unusual dwelling-place, had advanced to the 

 abnormal state of development which we call "a cystic worm/' 



Simultaneously with Dujardin (whose work, as Leuckart says, 

 was frequently made use of in Von Siebold's article " Parasiten," 

 in E. Wagner's ( Handworterbuch der Physiol./ Band ii, which, 

 although it bears the date 1844, did not appear until 1845), Von 

 Siebold expressed the same opinions in Germany, which were 

 supported by Dujardin on the other side of the Rhine. At 

 first, however (see l Lehrbuch der vergleichenden Anatomic,' 

 p. Ill), Von Siebold inclined towards Steeristrup's view, and 

 said, " In its form, its suckers, and its circlet of hooks, the head 

 of the asexual cystic worms possesses such a striking simila- 

 rity to the heads of certain tape-worms, that one is tempted to 

 believe that the cystic worms are nothing else than undeveloped 

 and larvae-form tape- worms." Had Von Siebold adhered to this 

 view, had he not allowed himself to be led, probably by Dujardin's 

 suppositions, to give up this simple idea, he would have saved 

 himself and science from a most unpleasant dispute. As he 

 himself says (art. " Parasiten/' pp. 650 and 676), however, he 

 subsequently arrived " at the most decided conviction that the 

 cystic worms are strayed tape-worms which have remained undeve- 

 loped and become degenerated, and of which the body grew out in 

 the foreign soil into a vesicle, without developing sexual 

 organs/' 



Independently of the authority of Dujardin, in France, and 

 of Von Siebold, in Germany, this view obtained the more ac- 

 ceptance, because Von Siebold, in proving his opinions, employed 

 as an example the fact, already known to the old helmintholo- 

 gists, of the identity of the Cystic, fasciolaris of the mouse with 

 the Tcenia crassicollis of the cat, and (as Creplin had previously 

 observed a metamorphosis of the asexual Schistocephalus dimor- 

 phus from the intestine of the stickleback, or from the liver of 

 the pike (Zeder's Cystic. Lucii, vide supra), into the sexual 

 Tricuspidaria nodosa in the intestine of certain water-birds) ex- 

 pressed the opinion that the cystic worm of the mouse, which, 

 according to him, was a strayed and degenerated tape-worm of 

 the cat, would be transformed into the T. crassicollis in the 

 intestine of the latter animal. " It is certain/' says he (1. c., 

 art. " Parasiten," p. 650), " that single individuals of the brood 

 of Tania crassicollis frequently stray into rodent animals, and 

 here degenerate into Cystlcercus fasciolaris, but when their 



