212 BOPYRIDA. 
pair are greatly elongated and furnished with very long ter- 
minal setee, 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 
seta. They are very active in this state. Whilst in the 
character of the head, which projects beyond and above 
the antennz, 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 antenne, 
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. 
