INTRODUCTION. 6 



pose in the first volume of the present work is to give 

 descriptions of the various parasitic Copepoda known 

 to occur on British fishes. The second volume will 

 contain the figures. 



We have not considered it necessary to enter into 

 a lengthened discussion on the structure and develop- 

 ment of the parasitic Copepoda ; this has already been 

 done by Dr. Baird and some other writers. Mr. C. B. 

 Wilson, in his various contributions dealing with the 

 Xorth American parasitic Copepods,has described them 

 very fully both in their histological and physiological 

 aspects. Moreover one of the authors of the present 

 volume (A. Scott) has published a Memoir con- 

 taining detailed accounts of a Lepeophtheirus and a 

 Lerndea, representing two important and diverse types 

 of the parasitic species.* 



GENERAL REMARKS ON DEVELOPMENT, ETC. 



The following general remarks concerning the 

 development and structure of these organisms are 

 derived chiefly from the works referred to above. 



The Copepod parasites of fishes are roughly divided 

 into two groups viz., those which in the adult stage 

 are free, that is, they can move about, at least to some 

 extent, from one part of the fish to another ; while 

 the others are permanently fixed. Lepeophtheirus 

 pectoralis may be taken as representing the first, and 

 Lerndea branchialis the second. 



The two groups taken together form a series which 

 exhibits remarkable variation in habits and structure. 

 While there is little to distinguish some of the 

 species at the one end of the series from free-living 

 non-parasitic Copepods, those at the other end exhibit 



* Liverpool Marine Biology Committee, Memoir No. VI : ' Lepeophtheirus 

 ' (1901). 



