1904-1905-] Copepoda living as Parasites or Messmates. 197 



VIII.— ^i\^ ACCOUNT OP SOME COPEPODA THAT 

 LIVE AS PARASITES ON, OP MESSMATES 

 WITH, OTHER INVERTEBRATA. 



By THOMAS SCOTT, LL.D., F.L.S., Honorary Member. 

 {Read March 22, 1903.) 



The study of animal or vegetable parasites is of never- failing 

 interest. In the course of such a study we meet with organ- 

 isms very different from each other, yet associated in various 

 relationships, either as friends or foes. The causes that have 

 brought about these associations, the purposes they serve in the 

 economy of nature, and the effects they may produce on other 

 living creatures that in any way come into contact with them, 

 are problems that may well engage our attention. So varied 

 • and strange are the relationships one meets with from time to 

 time, that the attempt to arrange and classify them is no easy 

 matter ; and we soon find that any system yet devised is at 

 best but a convenient makeshift. 



The term " parasite," as used here, includes various kinds of 

 relationships. In some, the species associated together may be 

 nearly akin ; in others, widely divergent. The relationship 

 may be that of a true parasite living on the body of its host, 

 or that of a commensal or messmate doing useful service in 

 return for food and shelter received. 



In a paper read to this Society two years ago I incidentally 

 directed your attention to some interesting Copepoda found 

 parasitic on several of our common fishes. In the present 

 paper I propose to give an account of a number of species found 

 for the most part associated with other invertebrates, and I have 

 arranged the species selected into six groups, as follows : — 



1. Copepoda usually found on sponges as commensals or 



messmates. 



2. Copepoda found only on Alcyonium or allied species, 



3. Copepoda found on various Echinoderms. 



4. Copepoda associated with Annelids. 



5. Copepoda found on other species of Crustacea. 



6. Copepoda that are associated with various species of 



Mollusca. 



