428 CRUSTACEA. 



eggs and embryos about between the valves of the shell. Ci/tJu-rr luti'it O. Fr. 

 Miiller, North Seas and Mediterranean. C. vtridls 0. Fr. Miill., North Seas. 



( 't/pris O. Fr. Miill. With median eye, but no heart. The shell valves are 

 light but strong, the anterior antennae have usually seven joints and are beset 

 with long seta?. The antenna of the second pair is simple and pediform. with 

 usually six joints. There are two pairs of legs, of which the posterior smaller 

 pair is bent upwards towards the dorsal surface. The caudal fork is very narrow 

 and elongated, and is provided with hooked setae at the point. The testes and 

 ovaries project between the lamella? of the shell. The male genital appa- 

 ratus has a peculiar mucous gland. Most of them inhabit fresh water. 

 CyjjrisfuscaStr., C.pubn-a 0. Fr. Miill., C.fHxi'dta JUT., and others. Notodromus 

 ininiai-hiift 0. Fr. Miill. 



Order 3. COPEPODA. * 



Entomostraca with elongated, usuallij well segmented body, without 

 shell-forming reduplicature of the skin, with biramous swimming feet ; 

 the abdomen is without appendages. 



The group of the Gopepoda includes a number of very different 

 forms. The non-parasitic members of the groups are distinguished 

 by a constant number of segments and paired appendages. The 

 numerous parasitic forms differ in various degrees from those which 

 lead an independent life ; in extreme cases some of them are so 

 modified, that without a knowledge of their development and the 

 peculiarities of their structure, they would rather be taken for 

 parasitic Worms than for Arthropods. The characteristic swimming 

 feet are, however, usually retained, though often reduced in number, 

 as rudimentary or modified appendages. When they are absent, the 

 developmental history gives a certain indication of the Copepod 

 nature. 



Appendages. The head seems as a rule to fuse with the first 

 thoracic segment ; and the cephalothorax so formed bears two pairs 

 of antenna?, a pair of mandibles, the same number of maxilla?, and 

 four maxillipeds, which last are only the external and internal branches 

 of a single pair of appendages (fig. 341) ; and finally the first pair of 

 swimming feet, which are not unfrequently modified in form. Then 

 come four free thoracic segments, each with a pair of swimming feet, 

 of which the last pair is frequently reduced and in the male may 

 be modified to assist in copulation. Finally, the fifth pair of feet and 



* 0. Fr. Miiller, ' Entomostraca seu Insecta testacea. qua? in aquis Dania? et 

 Norvegia? reperit. descripsit," Lipsia?, 1785. Jurine. ' Histoire des Monocles," 

 Geneve, 1820. W. Lilljeborg. " Crustacea ex ordinibus tribus : Cladocera, 

 Ostracoda et Copepoda, in Scania ocrurrentibus, 1 ' Lund., 1853. C. Glaus,." Zur 

 Morphologic der Copepoden," Wfirzb. unf unfits. Zcitxchr., I860. C. Clans., 

 Die freiiebenden Copepoden," Leipzig, ~ 



