PARASITES. 105 



tlieir pecular host. Thus the Ascaris mystax, the guest 

 of the domestic cat, lives in different species of FellSj 

 while the fox, so nearly resembling in appearance the 

 wolf and the dog, never entertains the Taenia scrrata, so 

 common in the latter animal. 



The same host does not always harbour the same 

 worms in the different regions of the globe which it 

 inhabits. This relates both to the parasites of man, and 

 to those of the domestic animals. Thus the large tape- 

 worm of man, which naturalists call Bothrioccj^halns, 

 is found only in Eussia, Poland, and Switzerland. A 

 small tape-worm, Tsenia nana, is observed nowhere 

 except in Abyssinia ; the Anchylostoma is known at 

 present only in the south of Europe and the north of 

 Africa ; the Filaria of Medina, in the west and the east 

 of Africa; the Bilharzia, that terrible worm, has only 

 been found in Egypt. 



There are also parasitic insects dreaded by man, as 

 the Chigoe (Pulex penetrans) which, happily, is only 

 known in certain countries. Some, however, have 

 become cosmopolitan, since man has introduced them 

 wherever he has established himself. 



The mammalia w^hich live on vegetable diet have 

 Ticnia without any crown of hooks, and man, according 

 to his teeth, ought only to nourish the Taenia medio- 

 canellata. We find in a work on the Algerian Taenia, by 

 Dr. Cauvet, that it is the Tsenia inermis, that is to say, 

 without hooks, which is the species common in Algeria. 

 Among fourteen taeniae which he had occasion to 

 examine, there was not a single Tsenia solium. I have 

 said long since, that this species ought to be less widely 

 spread than the taenia without hooks. The Taenia solium 



