36 ANIMAL PAHASITES. 



isolated proglottis of T. serrata creeping upon the wall of a room 

 at a height of several feet, named them Ovaria ambulantia. 

 When they still contain eggs the presence or absence of the 

 six-hooked embryos in these renders it easy to avoid error and 

 distinguish the proglottides from the true Trematoda. From the 

 considerable similarity of form of the two animals, it has 

 recently been attempted to regard all these proglottides as 

 Trematoda ; nay, many have even expressed the hope that it would 

 some day be possible to prove that the final destiny of the pro- 

 glottides was to become converged into Trematoda. Against this 

 notion I declare myself unconditionally, and even Van Beneden 

 appears only to intend to call attention to the mere relation of 

 form of the two animals, which, even in the time of Rudolphi, 

 must have sufficed to caucel the separation of the two forms into 

 Cestodea and Trematoda in Rudolphi's system. The experi- 

 ments of De la Valette upon the production of the Trematoda, 

 which will be mentioned by me hereafter, and the observation 

 that in the outer world, as in the intestinal canal of other 

 animals, the proglottides die rapidly, support the above refutation 

 of an intimate relationship between the Cestodea and Trematoda, 

 founded upon their development and not merely upon form. 

 By the advice of J. Miiller, I administered to three different 

 young dogs mature proglottides of the characteristic T. ex 

 Cysticerco tenuicolli. But on dissecting the animals eight, ten, 

 and fourteen days after the different administrations, I never 

 found the slightest trace of these proglottides, or of any trema- 

 tode forms. The proglottides had totally disappeared (by diges- 

 tion), and the very same thing had taken place in the intestine 

 of the rabbit when I had administered proglottides of T. serrata 

 to rabbits. Moreover, if we look more closely at the 

 essentially different anatomical structure of the two kinds of 

 animals, for, besides the different form and colour of the 

 eggs, and the different form of the embryos, the want of 

 calcareous corpuscles, the presence of a pair of lateral aqui- 

 ferous vessels with a pulsating tube at the posterior extremity 

 of the body in the Trematoda, in opposition to the four 

 lateral longitudinal vessels of the Cestodea, the pulsating 

 tube (communicating vessel) of which, should rather be sought 

 in their cephalic than in their abdominal extremity, and the 

 want of an alimentary canal in these animals, will prevent 

 us unconditionally from placing these two animal forms 



