MUTUALISTS. 71 



mammals. It has been said that the phthiriasis of the 

 cat is occasioned by the abundance of ricini. The 

 trichodectes of the dog has lately attracted the espe- 

 cial notice of naturalists, and that from the following 

 circumstances. 



There is no tape-worm more common in the dog than 

 the Tsenia cucumerina. But whence comes it ? How is it 

 introduced ? This, had been an enigma for many years, at 

 the time when I dissected some dogs infested with Tsenia 

 serrata, in the Museum of Natural History at Paris. 

 Together with the Tsenia serrata, the number and age of 

 which I knew beforehand, since I had myself planted them, 

 there were found in the intestines of one of the dogs 

 some individuals of the Tsenia cucumerina. My dogs had 

 taken nothing but milk, and cysticerci pisiformes. Were 

 there cysticerci of different kinds in the peritoneum of 

 the rabbit ? The veil is now withdrawn. We have just 

 said that the dog harbours a tick known under the name 

 of Trichodectes, and in this trichodectes lodges the 

 Scolex, we might even say the larva of the Tsenia 

 cucumerina. Dogs, especially young ones, lick their 

 hair continually, and it is by this operation that the 

 young tsenia is introduced. It is by a similar process 

 that the horse introduces the eggs of the OEstrus which 

 are hatched in its stomach. 



Many of these ticks live abundantly in birds, and 

 multiply rapidly. The Liothe pallidum lives on the cock, 

 the Liothe stramineum on the turkey, the Philopterus 

 falciformds on the peacock, the Philopterus clavijormis on 

 the pigeon. It is to be observed that every bird can 

 nourish many different kinds. Fig. 2 represents the tick 

 which infests the sea-eagle, called Pygarg. 

 5 



