ANIMAL PARASITES. 33 



Society of Saxon Lusatia, also, has repeatedly tested tins subject 

 by experiment, especially the Society at Klix, and its president, 

 M. Kind, of Kleinbautzen. 



Four months after I had made my first experiment, Leuckart 

 fed a colony of white mice with T. crassicollis. This appears to 

 have been in October, 1853. His experiment was forgotten until 

 the results obtained by Haubner and myself, in January, 1854, 

 were communicated to him by letter. When, upon this, he 

 examined his white mice, he found them infested by cystic worms. 

 (See Siebold and Kolliker's ' Zeitschr. fur Wiss. Zool./ vii, 

 p. 139.) 



It still remained to be tried whether it was possible also to 

 produce the other cystic worms artificially, and Haubner and 

 myself, as well as Leuckart subsequently, employed the experi- 

 ments made with this view, for the purpose of proving at the 

 same time the specific determinations undertaken by me. I 

 myself also proved that, by the administration of the above- 

 mentioned mature species of Taenia as far as they were accessible 

 to me, to suitable animals, only the cystic worms belonging to 

 these species can be reared, but not any kind of cystic worm at 

 pleasure. In his most recent and excellent work Leuckart has 

 proved that every one of these species presents such essential 

 differences, even by the first processes in the conversion of the 

 brood into the forms in question, that we can only speak of 

 their identity if we are willing to give up altogether the idea of 

 species in zoology, or not to see the differences. 



Very recently, in Gurlt's ' Magazin fur Thierheilkunde/ 

 Professor May, of Weishenstephan, has made known some expe- 

 riments from which it might appear as if such specific distinctions 

 did not exist. But an exact criticism, such as I have given in 

 the appendix to the work upon Cysticercus tenuicollis, proves the 

 inadmissibility of May's statements, the deficiency of his know- 

 ledge of systematic determination, and the faultiness of the mode 

 in which his experiments were made. To cite only one cir- 

 cumstance in support of these assertions, I may mention that 

 May believes he reared Tcenia solium in the intestine of the dog, 

 from Cysticerci celhdosa which he had preserved for ten days in 

 water at a temperature of about 10° R. (=48° F.) Although I 

 regarded this experiment as contradictory to nature, merely 

 because the infected mouse which a cat is about to devour, or the 

 rabbit which a dog is going to eat, is not laid by these animals 



c 



