294, A HISTORY OF RECENT CRUSTACEA 
are no chelate limbs to which the terms chelipeds or gnatho- 
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 antennze of insignificant size, while in the 
males they are developed to a great 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 pereeopods, 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 specific value. 
The upper antennze of the Cumacea are always small, 
with two diminutive flagella, of which one is sometimes 
evanescent. ‘The upper lip is a single lobe between the 
bases of the lower antennae. The lower lip forms two 
