52 OF THE PR[NCIPAL WOUMS 



which vary in the different periods of the life of the 

 worm. 



The same may be said of the lateral papillae 

 and of the borders, as well as of the knots, parts 

 which are not seen in the joints of the young tae- 

 nia without a good microscope ; thfty become visi- 

 ble only as the worm grows. It is equally true that 

 those who would establish systematic divisions, 

 on characters not less vague and uncertain, have 

 fcast a shade over those questions which they ought 

 to have elucidated. 



Thus several celebrated naturalists reposing 

 too much confidence in certain vague characters, 

 have confounded the species, and that they might 

 follow the order of nature, they have been anxious 

 to make these characters too distinct.(.T6) 



If there are in the taenia certain fixed charac- 

 ters, immutable in every age of the worm, visible 

 to the naked eye, we see them in the head of some 

 armed with fangs or crotchets, as we have noticed 



above. (57) 



On these characters, which may be called spe- 

 cific. Block formed the division of all the intestinal 

 taeniae, into the armed and unarmed taeniae, a di- 

 vision still more appropriate for the human taeniae. 

 This division, besides that it is not subject to uncer* 

 tain changes, is much more beneficial to physicians. 

 Practitioners are not ignorant that the armed tae- 

 nia, by insinuating itself into the mucous membrane 

 of the intestines, with greater force than the unarm- 

 ed taenia, produces in parts thus sensible sharp 



