PARASITES FREE DURING THEIR WHOLE LIFE. 113 



A very skilful naturalist, Mons. Yaillant, has lately 

 made these animals the subject of study. Mr. Baird, in 

 1869, made known four new Pontobdellas, one from the 

 coast of Africa, two from the straits of Mag'ellan, and 

 one from Australia, found in one of the Ehinobatidse. 

 But the most interesting in every point of view are the 

 Branchellions, which inhabit the electrical fishes known 

 under the name of torpedoes, and which do not fear to 

 choose an electric battery as a place of abode. These 

 branchellions always attach themselves, as it appears, 

 to the low^er surface of the body, and not to the gills as 

 has been thought; and they are distinguished from all 

 their congeners by tufts of filaments along their sides, 

 wdiich have been compared to lymphatic branchiae. 



Many naturalists have considered these curious worms 

 worthy of attention, and have made many interesting 

 observations upon them. One of the finest memoirs 

 en this subject is that of Mons. A. de Quatrefages. We 

 may here mention, in connection with their mode of life, 

 that neither Leydig nor Quatrefages found globules of 

 blood in their digestive cavity. The branchellions live 

 on the mucous products of the secretions of the skin, and 

 instead of being parasites, we may consider them as 

 worms paying liberally for the room which they occupy in 

 their host, by maintaining his skin in good condition. 

 They ought rather to be classed among animals which 

 render service to others ; that is, among mutualists. 



In the fresh waters of Europe, a little leech-like 

 animal, beautiful both in form and colour, fixes itself 

 on carps, tenches, and other Cyprinidse ; this is the 

 Piscicola geometra, which also lives on the Silarus glanis. 

 They are sometimes found in such great numbers that 



