84 ANIMAL PARASITES AND MESSMATES. 



liarity, that while one increases rapidly the other be- 

 comes atrophied. 



An Egyptian distome, which lives in man, gives an 

 instance of this peculiarity, as well as the D. Jilicolle, 

 which inhabits a fish (Brama Rail). The caligi which 

 live on the skin of fishes are, when young, fastened by a 

 cord which comes from the anterior edge of their cara- 

 pace : while quite little, they put themselves under the 

 protection of a kind neighbour, and allow themselves to 

 be led by him. 



The new tubularia, which we have dedicated to our 

 learned colleague Dumortier, often fixes itself on the 

 carapace of ordinary crabs, and causes itself to be con- 

 veyed like the Echeneis; the tubulary observed by 

 Gwyn Jeffreys, close by the eye of the Rossia papilUfera, 

 a cephalopod mollusc, perhaps belongs to the same 

 species. 



Every colony of campanularise or sertulariae lodges a 

 crowd of messmates and mutualists; and there are a 

 great number of crustaceans and polyps of all sizes 

 which serve as an abode for infusoria of every kind. 

 Some establish themselves on the carapace or on the 

 swimming appendages, as in a carriage ; others on one 

 of the gills, which renders their mode of life more easy, 

 and the danger less great. An amphipod very exten- 

 sively spread over our sea-coasts, the Gammarus marinus, 

 usually has its appendages covered with Vayinicola 

 crystaUina, 



