FUNDAMENTAL RELATIONS OF ANIMALS 125 



such as the Ant-Hill Insects, the Clavigers, the Cleri, and Bees. 

 Different kinds of Ants live together, if not as parasites one upon 

 another, at least in a kind of servitude. Other Insects live upon the 

 bodies of warm-blooded animals, such as the Fleas and Lice, and 

 of these the number is legion. Some Hydrachnas are parasitic upon 

 aquatic Mollusks. 



Among Crustacea there are Crabs constantly living in the shell of 

 Mollusks, such as the Pinnotheres of the Oyster and Mussel. I have 

 foimd other species upon Sea-Urchins {Pinnotheres Melitta, a new 

 species, upon Melitta quinqiiefora). The Paguri take the shells of 

 Mollusks to protect themselves; while a vast number of Amphipods 

 live upon Fishes, attached to their gills, upon their tongue, or upon 

 their skin, or upon Starfishes. The Cyamus Ceti lives upon the 

 Whale. Some Cirripeds are parasites upon the Whales, others upon 

 Corals. In the family of Lernasans the females are mostly parasites 

 upon the gills or fins or upon the body of Fishes, while the males 

 are free. 



Among Worms this mode of existence is still more frequent, and 

 while some dwell only among Corals, entire families of others con- 

 sist only of genuine parasites; but here again we find the most 

 diversified relations; for, while some are constantly parasitic, others 

 depend only for a certain period of their life upon other animals 

 for their existence. The young Gordius is a free animal; it then 

 creeps into the body of Insects and leaves them again to propagate; 

 the young Distoma lives free in the water as Cercaria and spends 

 the remainder of its life in other animals; the Tasnia, on the con- 

 trary, is a parasite through life, and only its eggs pass from one ani- 

 mal into the other. But what is most extraordinary in this, as in 

 many other intestinal Worms, is the fact that while they undergo 

 their first transformations in some kind of animals they do not reach 

 their complete development until they pass into the body of another 

 higher type, being swallowed up by this while in the body of their 

 first host. Such is the case with many Filarial, the Taeniae and Bothro- 

 cephali. These at first inhabit lower Fishes, and these Fishes being 

 swallo^ved by Sharks or Water Birds, or Mice with their Worms 

 being eaten up by Cats, the parasites living in them undergo their 

 final transformation in the latter. Many Worms undertake extensive 

 migrations through the bodies of other animals before they reach 

 the proper place for their final development. 



