254 ENTOZOA. 



General and Specific Characters. — A remarkably small cestode helmintli, seldom ex- 

 ceeding tlie fourtli of an inch, in length and developing only four segments including 

 that of the head ; cephalic extremity capped by a pointed rostellum, ai-med with a double 

 crown of comparatively large-rooted hooks, from thirty to forty in number ; the four 

 suckers prominent, and succeeded by an elongation of the cephalic segment forming the 

 neck ; final segment, when sexually mature, equaUing in length the three anterior ones ; 

 reproductive papilla at the margin of the proglottis below the central hne ; proscolex or 

 embryo forming large proliferous vesicles, in which the scohces (== echinococous heads) 

 are developed by gemmation internally. 



TMs little tapeworm (in its strobila condition) infests only the 

 dog and wolf, but its well-known larvas, constituting tlie so-called 

 hydatids of medical writers, are of very frequent occurrence in the 

 human body. These hydatigenous formations, according to the 

 particular features they may happen to present, or in accordance 

 with the fancy of the writer, are sometimes called acephalocysts, 

 echinococci, echinococcus vesicles, pill-box hydatids, etc. 



Following Kiichenmeister, it has been supposed by Weinland and 

 others that there are two distinct forms of Echinococcus severally 

 referable to different tapeworm-species, one of which is, on all hands, 

 admitted to be Yon Siebold's Taenia echinococcus, the other an un- 

 known Taenia, also supposed to infest dogs. That Echinococci vary 

 much, both in regard to the number of cephalic hooks they display at 

 certain intervals of growth, and also in respect of the mode of evo- 

 lution of the scolices, few will deny ; but, according to Leuckart, we 

 are not therefore warranted in accepting Kiichenmeister' s view as 

 to the specific distinctness of certain forms. Like Weinland, I had 

 been, in the first instance, led away by Kiichenmeister' s autho- 

 rity, although I had enjoyed abundant opportunity of investigating 

 these singularly interesting larvEe. The grounds on which Leuckart 

 disputes Kiichenmeister' s view are, to my mind, perfectly satis- 

 factory ; for he shows conclusively that the proportional number 

 of hooks fluctuates in both forms, that is, in Kiichenmeister' s 

 Echinococcus scolicipariens and altricipariens ahke, whilst the 

 alleged differences in the size and character of the hooks themselves 

 have reference to their degree of development (" Die menschhchen 

 Parasiten," s. 328, et seq.). If this view be generally accepted, it 



