CHAPTER X 

 CRUSTACEA AS PARASITES AND MESSMATES 



THE life of every animal is in more or less 

 intimate relation with that of all the living 

 creatures which surround it. Some serve for its 

 food, or supply it with shelter or foothold ; others 

 prey upon it, or compete with it for the necessaries 

 of life ; and others, again, influence it for good or 

 evil in countless ways more subtle than these, but 

 equally important. There are some associations oi 

 a closer and more enduring nature, to which the 

 names of Symbiosis, Commensalism, and Parasitism, 

 are applied, and it is with examples of these that 

 the present chapter is concerned. 



The term Symbiosis is strictly applied to an inti- 

 mate physiological partnership, such as we find in 

 some of the lower animals and plants, and in this sense 

 there are no truly symbiotic Crustacea. The word, 

 however, is sometimes used, in its literal sense of a 

 "living together," to embrace all cases of animals 

 living together for mutual advantage. Commen- 

 salism means, literally, " sitting at the same table," 



207 



