294 A HISTORY OF EECENT CRUSTACEA 



are no chelate limbs to which the terms chelipeds orgnatho- 

 pods would be applicable. 



The adult males are very strikingly distinguished from 

 the females in more than one particular. Thus, the females 

 have the lower antennae of insignificant size, while in the 

 males they are developed to a gi-eat length, though they 

 are not always very apparent, as they are often securely 

 tucked away along the sides of the body, an arrangement 

 which seems to imply that they are of exceptional value, and 

 possibly also only of exceptional use. Again, the females 

 never have pleopods, while the males have them, except in a 

 single genus, throughout six of the eight families. More- 

 over, in all the families but one the males have well- 

 developed exopods or swimming-branches attached to all 

 the first four pairs of perseopods, whereas the females never 

 have them on more than three pairs, and sometimes only on 

 one or two. These disparities are connected with the habits 

 of the animals. For at night-time it is found that the sur- 

 face-net in suitable localities will secure the males of certain 

 species in abundance, not intermingled with any females. 

 The latter sex, on the other hand, is generally found to 

 preponderate when their settlements in the sand and 

 mud are invaded. The females are evidently of a less 

 roving disposition than their mates. Yet their movements 

 are not destitute of considerable liveliness and energy. To 

 compensate them, too, for their inferior swimming appara- 

 tus, they very commonly have the carapace ornamented 

 with various spines and tubercles, which may be supposed 

 to form a sort of defensive armour against some of their 

 foes. The more active males, on the contrary, seem to 

 find their advantage in having the carapace smooth. To 

 the student this last distinction is not a little embarrassing, 

 for much smaller differences than those which here mark 

 the external appearance of the two sexes have frequently 

 been allowed sjiecific value. 



The upper antennge of the Cumacea are always small, 

 with two diminutive flagella,^)f which one is sometimes 

 evanescent. The upper lip is a single lobe between the 

 bases of the lower antennic. The lower lip forms two 



