INTRODUCTION. 6 



lists of specific synonyms, this, in the case of species 

 known to the older authors having been excellently 

 done by Dr. Baird. I have, however, given as fully 

 as possible references to the descriptions of more 

 recent observers, and when practically useful, also to 

 those of older date, omitting such only as seemed to 

 be of slight or merely literary interest. A list of the 

 memoirs from which these details are taken is printed 

 at p. 27. 



The great majority of the Copepoda are free swim- 

 ming species, a considerable number, however, being 

 truly parasitic and living suctorially on the juices of 

 Fishes, Annelids, Crustacea, and other aquatic animals. 

 These do not enter into the scope of the present work. 

 Another group, which may be called semi-parasitic, is 

 found living (not suctorially nor attached in any way 

 to the body of the host, but moving freely) in the 

 cavities of various marine animals, notably in those of 

 Ascidians, both simple and compound. The genera 

 Notodelphys, Botachus, Ascidicola, Doropygus, Licho- 

 molgus, and Notopterophorus are among the most 

 important of this group. M. Hesse, of Brest, has 

 closely studied these animals, and has described many 

 species ; as also have MM. Claparede, T. Thorell, Van 

 Beneden, and others. Some species have also been 

 found, perhaps living suctorially though this is open 

 to doubt on the outer surfaces of sponges, sea- 

 urchins, and star-fishes ; to this list belong some 

 members of the genus Artotrogus. These semi- 

 parasitic Copepoda exhibit for the most part a 

 transitional condition of the mouth organs, inter- 



