652 



ORDINARY TAPE-WORMS (CYSTOIDEl). 



truth an animal, and the young stage of a tape-worm, yet the multi- 

 locular form was still regarded as a tumour. Now, however, this error 

 has been dissipated, and our knowledge of this important parasite has 

 attained a fairly satisfactory completeness and certainty. 



DIVISION II. Ordinary Tape-Worms (Cystoidei). 



As we have already noted (p. 360 and p. 400), this group includes 

 all those Tcenice which are not cystic tape-worms. They do not, how- 

 ever, form a single well-defined group, but rather include many diverse 

 types. They are distinguished from the cystic tape-worms by the 

 manner of their development, i.e., by the absence of a proper bladder- 

 worm stage. They possess, indeed, usually a larval stage somewhat 

 resembling the bladder-worm, but this is so small, and its bladder is 

 so little developed, that in spite of the resemblance the term " bladder- 

 worm " is hardly applicable. Strictly speaking, the embryonic body 

 of this young stage (Cysticercoid) cannot be regarded as the bladder, 

 since it is solid, and has not that accumulated fluid which suggested 

 the theory that the true bladder-worm was a dropsical degeneration. 



The " bladder " is, however, usually distinctly marked off from the 



Fio. 336. Cysticercus arionis, with (A) retracted 

 and (B) evaginated head. ( x 50.) 



FIG. 337. Cysticercus gtomeridis, 

 after Villot. (x 50.) 



rest of the tape-worm body, and is, even in the extended state, recog- 

 nisable as a distinct structure. It possesses a more or less firm, some- 



