228 Illinois State Laboratory of Natural History. 



In Epischura, as in the other three genera, the cephalotho- 

 rax is six-segmented. All of the swimming legs have a 

 three-segmented outer, but a one-segmented inner, ramus. 

 In the female the inner ramus has entirely disappeared in 

 the fifth pair of legs, and the outer ramus is two-segmented. . 

 In the male also the fifth pair of legs are without inner rami, 

 and the outer ramus of the right leg is two- or three-segmented, 

 that of the left leg three-segmented. A peculiarity of this 

 genus is the modification of the abdomen of the male into a 

 clasping organ. The abdomen of the female is also modified 

 in at least one species (lacustris). 



So much for the relationships indicated by the structures 

 considered. According to the above, Osphranticum must be 

 regarded as the most primitive form, Epischura as the most 

 modified, and Limnocalanus and Diaptomus as occupying an 

 intermediate position. I think that the mass of charac- 

 ters will support this statement, although there are other 

 characters which would lead one to doubt somewhat its 

 correctness. For example, in Osphranticum and Diaptomus 

 the females carry the eggs in an egg-sac, while in Limnocal- 

 anus and Epischura they do not. In Osphranticum, I>iaj>tn- 

 mus, and Epischura the spermatophore persists tor some time ; 

 but I have not seen a single female Limnocalanus with a 

 spermatophore, although according to Giesbrecht the fertili- 

 zation by means of a spermatophore is about the only charac- 

 teristic which all Copepoda have in common.* 



The material at my command for the preparation of this 

 paper has been complete; that is to say, I have had speci- 

 mens of all the known species of the genera treated, ami 

 access to the most recent literature. The collections exam- 

 ined belong in great part to the Illinois State laboratory of 

 Natural History, in part to Prof. Frank Smith, of the Univer- 

 sity of Illinois, and in part to myself. The following localities 

 are represented : Norway, the Caspian Sea, Lake Sitai and 

 the Whangpoo River in China, Newfoundland, and the Stati - 



* "The sexually mature individuals are to some extent mi transformed by para- 

 sit ism that unless the fertilization by menus of spermatophores be excepted they seem 

 tn have no characteristic common to all which would at the same time distinguish the 

 (inter Copepoda from the other orders of Entomostraca." (Giesbrecht, '5)2. p. i 



