104 ANIMAL PARASITES AND MESSMATES. 



great care of the skin of their host, and use it sparingly. 

 Some also are found which cannot live without assist- 

 ance, but repay it with some service. Often, indeed, 

 they associate with their host, and live on a footing 

 of perfect equality with him; and besides these are 

 found associations in which equality is by no means 

 recognized, and where labourers or even slaves perform 

 the work disdained by their masters. 



In the last category we shall arrange true parasites, 

 which take both their lodging and their food. And here, 

 again, we shall meet with three distinct subdivisions. 



The first includes those which travel from one hotel 

 to another before they arrive at their destination ; 

 to-day they lodge in a prawn, to-morrow in a gudgeon, 

 then in some fish which preys upon others, as the perch 

 or the pike. These are nomadic parasites, which do not 

 stop or think of family life until they have found the 

 hotel for which they are destined. 



Sometimes the parasite gets into a wrong train, and 

 not being able to retrace his steps, he remains at a 

 station where no other train will take him up. He is 

 condemned to die in a waiting-room. 



In the last subdivision, we have parasites that have 

 arrived at their destination, occupying themselves in 

 future only with the joys of a family. 



Thus we find some which are really at home, and 

 others which are on their journey, sometimes on the 

 right road, and at others, wandering and lost in an alien 

 " host." The former are autochthonic parasites, the 

 others are. foreigners. We may say that each animal 

 species has its proper parasites, which can live only in 

 animals which have at least more or less affinity with 



