582 DESCRIPTION OF THE SUBGENUS ECHINOCOCCIFER. 



rudimentary head into the segmented tape-worm. I have established 

 this fact by comparison of the hooks of the Echinococcus from the cow 

 with those of the tape- worm from the same parasite, and in unripe 

 Tcenice (of the third week) I found perfect intermediate forms between 

 the structure of the Echinococcus-hQ&d and the developed Tcenia. 



As is sufficiently shown in the preceding figures, the difference 

 between the hooks of the bladder-worm and those of the Tcenice of 

 Echinococcus have to do exclusively with the roots. The structure 

 of the claws is the same in both, but the root-processes are short and 

 slender during the bladder-worm stage, while in the adult tape-worms 

 they are not only considerably longer, but have also a stouter form. 

 Sometimes even in hooks of the same Tcenia one finds differences 

 in the length and thickness of these processes, and similar differences 

 are to be found in the Echinococcus-hQ&fa. In rare cases I have seen 

 in the latter an approximation to the form of the tape-worm hooks, 

 i.e., to a more perfect development of the roots. 



This late or even secondary development of the hooks in Echino- 

 coccus brings it to pass that the roots are characterised by an other- 

 wise hardly perceptible variability in size and form. It is only 

 necessary to take a cursory glance at the examples given by Krabbe 

 on the third plate of his memoir on Echinococcus, in which there are 

 displayed not less than forty-two figures of large and small hooks, 

 showing how widely the extremes may differ from one another. 

 Many of the forms may indeed be explained as malformations, but 

 the frequent occurrence of others proves them to be normal. If we 

 compare them more closely, we soon see that the deviations consist 

 mainly in the more or less abundant deposit of chitin on the roots 

 of the hooks, through which deposit the latter sometimes increase in 

 length, and sometimes become gnarled and thickened. 



With the demonstration of this late development, the most im- 

 portant of Kiichenmeister's arguments in favour of the validity of his 

 species lose their cogency, and they were indeed the only arguments 

 which we had to consider in deciding this question, for the above 

 mentioned differences in proliferation were from the first seen to have 

 only a doubtful value. 



Such being the state of the case, even in the first edition of this 

 work, I expressed myself most decidedly against Kiichenmeister's 

 opinion, and maintained that the various forms of bladder- worm were 

 only varieties of a single species. The proposed change was not only 

 of fundamental importance in reference to our opinions as to the 

 nature and history of Echinococcus, but had a further practical im- 

 portance since Kuchenmeister claimed for his two species two different 

 tape-worm forms, differing not only in structure, but also in host. 



