Ceap. I. PARASITIC ANIMALS. 125 



and Bees. Diflbrent kinds of Ants live together, if not as parasites one upon anotlier, 

 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 Ilydrachnas are pai'asitic 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 found other species upon 

 Sea-Urchins, (Pinnotheres Melittiv, a new species, upon Melitta quinquefora). 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 Lernseans, 

 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 consist only of genuine parasites; 

 but here again we find the most diversified relations; for, while some are con- 

 stantly parasitic, others depend only for a certain period of their life upon other 

 animals for their existence. The 3'oung 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 TiBnia, on the contrary, is a parasite through life, and only its eggs 

 pass from one animal 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 develop- 

 ment 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 Filariae, 

 the Tamitc and Bothrocephali. These at first inhabit lower Fishes, and these Fishes 

 being swallowed 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 i^lace for their iiiial development.^ 



* NiTzscn, (CiiK. L.,) Darstellung <ler Familien Die Pflanzen-Liluse, Aphiilon, Niirnberg, 1846, 8vo. 



unci Gattungen der Tliierinsekten, Halle, 1818, 8vo. fig. — Duges, (Ant.,) Recherches sur Tordre des 



— IIayden, (C. v.,) Versuch einer sj-stematiscben Acariens, Ann. Sc Nat., 2de ser., 1834, I., p. 5, II., 



Einllieiluiig der Acariden, Isis, 182(3, p. 008. — p. 18, fig. 



Ratze.nui-kg, (J. S. C.,) Die lelmeumonen der * I have found a new genus of this family upon 



Forstinsekten, Berlin, 1844-52, 3 vols. 4to. fig. — Asterias Ileliantlioides. 



Clark, (Bk.,) Observations on the Genus Oestrus, ' See above, p. 7G, note 1 ; Siebold, Wanderung, 



Trans. Lin. Soc., HI., p. 289, fig. — Kocii, (C. L.,) etc., p. 77, note 1 ; Steenstui;!', etc. 



