406 SUBGENUS CYSTOT^ENIA T^ENIA SAGINATA. 



peculiarities. This is above all true of the hooks, whose form, size, 

 and number, though variable to a certain extent, are so characteristic 

 of the different species, that on them alone one can, after some practice, 

 establish a diagnosis. Not less distinctive are the differences in the 

 anatomical structure, especially of the generative organs, and in the 

 development, as we shall afterwards see, in the case of the forms which 

 specially interest us. But granted that it were possible to explain 

 all the differences between Cysticercus celluloses and C. tenuicollis or 

 Coenuriis,OT those between Tcenia solium and T. marginata or T.canurus, 

 on the theory of the variability of species a theory which might with 

 equal justice be considered as overturning all systematic zoology yet 

 one fact alone is enough to forbid the identification of the two forms. 

 This fact is the result of experiment. The attempt to give a sheep 

 staggers with eggs of T. solium or T. serrata yields no result, but 

 after administering the ripe proglottides of T. cosnurus, we are not 

 only sure of the result, but can predict the date of the appearance of 

 the first symptoms with almost mathematical precision. By the oft- 

 repeated experiments of Haubner, Baillet, myself, and others, it has 

 been indisputably shown that certain bladder-worms always result 

 from certain eggs, and pass into definite tape-worm forms. Besides, 

 when one occasionally finds all the three tape-worms of the dog in the 

 same intestine without any loss of their characteristic peculiarities, 

 one can hardly persist in regarding them as mere varieties, owing 

 their special form directly to the circumstances of their life. 



a. Cystic Tape-worms without Circlet of Hooks. 

 (Taeniarhynchus, Weinland.) 



Taenia saginata, Goze. 



(Taenia solium, Auct. p. p., Taenia lata, Auct. p. p., Taenia dentata, Batsch, 

 Taenia mediocanellata, Kuchenmeister. ) 



Goze, " Eingeweidewurmer, &c.," p. 269 (T. cucurbitina, grandis, saginata). 



Kuchenmeister, "Cestoden, &c.," p. 107, tab. ii., 1853 (T. mediocanellata). 



Idem, "Parasiten," first German edition, p. 88 ; second edition, p. 140 (T. media- 



canellata). 

 Leuckart, "Parasiten," first German edition, Bd. i., p. 258 (T. mediocaneUata). 



This is the largest of the human Taeniae, and when extended measures 

 7 or 8 metres, but in its contracted state is only about 4 metres long ; 

 it is composed of from 1200 to 1300 segments, of which more than three- 

 fourths belong to the anterior half of tlu body. But it is not its length 

 alone that characterises this worm ; it is also of unusual breadth and 

 thickness, and is provided with segments which arc remarkable for their 



