PARASITES. 95 



by multiplying in granaries. There are even worms 

 which lodge in certain of the graminacese, and get com- 

 pletely dry with the envelope which contains them, 

 without ceasing to live. Their life is suspended till the 

 day when the seed is sufficiently softened in the earth or 

 the water. 



"We have seen that each parasite has its host : we 

 must have a particular name to designate it. But that 

 does not imply that if it find not its dwelling-place it 

 must perish. It may only live some time at the 

 expense of its neighbour, and thus pass for its parasite. 

 Naturalists are occasionally deceived. Thus, they once 

 believed in the passa.ge of the Schistocephalus of the 

 stickleback into the intestines of certain birds which 

 eat them, and in which they are only found accidentally. 

 The Ligulae of the Cyprinidse, found in the intestines of 

 the cormorant or the goosander, are not, in our opinion at 

 least, worms peculiar to these birds. They are strangers 

 which must either emigrate again or die. Acari which 

 originally belonged to mammals and birds, have been 

 found living on man, causing prurigo, or even serious 

 maladies, and yet these parasites are not regarded as 

 peculiar to our species. We might cite other examples. 

 Who has not been annoyed by the flea, which abandons 

 for an instant the dog, its natural host ? 



Among these free parasites, many do not attach 

 themselves to a particular species, and well deserve 

 the title of cosmopolitan parasites. Thus we see 

 that the Ascaris lumbricoides, so common among child- 

 ren, lodges also in the ox, or the horse, the ass, and 

 the pig. The Distoma hepaticum, which is a parasite 

 peculiar to the sheep, if we may judge by its abundance 



