ANIMAL PARASITES. 25 



that is to say, furnished with the armature of the head of mature 

 Tceniae, aud also with the commencement of segmentation, have 

 reached some place exterior to the intestine of a certain animal, 

 and become dropsical by the accumulation of water in the 

 posterior, otherwise jointed part of the body. R. Leuckart 

 himself calls his views put forward in 1818 in Wiegmann's 

 'Archiv' (xiv Th., i, p. 7), and subsequently in 1852 (in Vierordt's 

 ' Archiv fur physiol. Heilkunde/ xi, p. 404, art. " Parasiten und 

 Parasitismus"), nothing but a paraphrase of the assertions of 

 Dujardin and Von Siebold. In his most recent work ('Die 

 Blasenbandwiirmer/ p. 21) he regrets having supported this 

 theory, from ignorance, both of Goeze's statements with regard to 

 the production of Cysticercus fasciolaris (vide supra) and of Guido 

 Wagener's discoveries (' Enthelminthica, Dissert, inaug./ Berol., 

 1848, p. 30), by regarding the flat bands (frustula of the older 

 writers) which hang down freely into the vesicle of Cysticercus 

 tenuicollis as the remains of the previous body of the tape-worm, 

 separated by the increasing dropsical disease. 



In 1850, the celebrated Belgian zoologist, Van Beneden (' Les 

 Vers Cestoides ou Acotyles/ Bruxelles, pp. 83 and 81), declared 

 the vesicular worms to be larva-like young states (scolices) of 

 Taenia, und compared them with the larvse of Tetrarhynchus 

 (that is, with the Anthocephali of the older writers), without 

 supporting this assertion empirically. According to him, the 

 head of the tape-worm (scolex) is produced from the egg of the 

 tape- worm. If an egg of a tape- worm reaches the intestinal 

 canal of an animal in which it may be further developed without 

 interruption, the jointed mature tape- worm (strobila) immediately 

 grows from the egg in uninterrupted succession ; but if it does 

 not reach an intestine of this kind, a longer or shorter period of 

 rest ensues in the further development, as soon as it has arrived 

 at the evolution of the head of the tape-worm (scolex) ; in this 

 case the anterior part of the head (scolex) then sinks into its 

 inflated hinder part, and it becomes a Cysticercus, or a cysticercal 

 animal-form. 



Here, however, we find two errors — 1, it is by no means 

 proved that a tape-worm can pass through all the separate phases 

 of its development in the intestine of its host; 2, and just as 

 little as the caudal vesicle is produced subsequently by dropsical 

 degeneration (Dujardin and Von Siebold) does the ready-formed 

 head sink into its inflated hind part, in order to become a Cysti- 



