212 BOPYRIIXE. 



pair are greatly elongated and furnished with very long ter- 

 minal setae, which are used as powerful organs of locomo- 

 tion ; the legs are short, but strong and prehensile, and 

 the tail is furnished beneath, at the sides, with five pairs 

 of flattened, oval, ciliated appendages, those of the sixth or 

 last segment being elongated, and terminated by a pair 

 of slender styles, which are armed at the tips with long- 

 setae. They are very active in this state. Whilst in the 

 character of the head, which projects beyond and above 

 the antennae, and in the form of the last three pairs of 

 legs, there is a close approximation to the larval form of 

 the parasitic Amphipoda forming the group Hyperina. 



It hence appears that the earliest or larval con- 

 ditions of these parasites is their highest and most 

 advanced stage ; the organs of sense and motion being 

 proportionately larger and better developed at that 

 period of their existence than ever after. 



It would thus appear as if the nervous energy were 

 then greater, and that the growth of both males and 

 females is but, what Dana calls, a vegetative process, and 

 one that is destructive of cephalization, which decreases in 

 proportion to the growth of the animal. We therefore 

 argue that, of the adult Bopyri, the smaller male ought 

 to be taken as typical of the species rather than the 

 more abnormal female.* 



The two families proposed by Mr. Milne Edwards, 



* This principle seems, indeed, capable of extension, since wherever 

 amongst the Articulata an animal exhibits the sexual organs, or those which 

 more especially characterize the sex, in an unusual state of development, the 

 opposite sex is necessarily more decidedly typical of the group to which the 

 species belongs. Thus, among moths, the immensely pectinated antennae, 

 and the more decided shape of the wings of the males, render the females 

 better exponents of the groups to which they respectively belong than the 

 males ; whereas in the genera Orgyia among the moths, Cebrio and Drilus 

 among beetles, Coccus among the Homoptera, in all which, for sexual pur- 

 poses, the wings remain undeveloped, and the body becomes dilated to an 

 enormous size filled with eggs, the opposite necessarily takes place. 



