ANIMAL PARASITES AND MESSMATES. 



673 



The most interesting fixed messmates are those cirrij^eds or bar- 

 nacles which, under the names of Coroiiula and Tahicinella (Figs. 3 

 and 4), cover the skins of whales. They are, like all the rest, free while 

 young, but later they take shelter on the back or on the head of one of 

 these huge cetaceans, and, having once chosen their abode, are after- 

 ward permanent tenants. Each whale lodges a particular species, and 



i''iG. 3. Cor.oNET Habnacle ^Cwonxila diadema). 



the manatee, marine turtles, and various sea-snakes, have also their 

 different sorts. Others establish themselves on their own immediate 

 relations and on other crustaceans. A pretty genus found near Cape 

 Yerd, living on the carapace of a large lobster, spreads itself over the 



Fig. 4. BuKROwiNG Barnacle {Tubicimlla traclimlis). 



centre of the lobster's back, and looks not unlike a bouquet of flowers. 

 Fig. 5 shows a fixed messmate attached to a sertularian. 



Mutualists, as the name suggests, are animals which live on each 

 other ; and, though usually confounded with messmates and parasites, 

 they diflfer from both in making some sort of return for benefits ob- 

 TOL. Tin. 43 



