336 
SEXUAL SELECTION. 
Part H- 
minute shields or cell-like bodies, which exhibit beaU' 
tiful changing colours ; these being absent in the 
females, and in the case of one species in both sexes. 
It would, however, be extremely rash to conclude that 
these curious organs serve merely to attract the females- 
In the female of a Brazilian species of Gela-simus, the 
whole body, as I am informed by Fritz Muller, is of fl 
nearly uniform greyish-brown. In the male the posterior 
part of the cephalo-thorax is pure white, with the 
anterior part of a rich green, shading into dark brown - 
and it is remarkable that these colours are liable t° 
change in the course of a few minutes— the whit 0 
becoming dirty grey or even black, the green “losing 
much of its brilliancy.” The males apparently a * 0 
much more numerous than the females. It deserve* 
especial notice that they do not acquire their bright 
colours until they become mature. They differ a '* 0 
from the females in the larger size of their cheh 0 - 
In some species of the genus, probably in all, th 0 
sexes pair and inhabit the same burrow. They a r0 
also, as we have seen, highly intelligent animate' 
From these various considerations it seems higb^ 
probable that the male in this species has becon ,e 
gaily ornamented in order to attract or excite tl' e 
female. 
It has just been stated that the male Gelasimus doe* 
not acquire his conspicuous colours until mature o lH 
nearly ready to breed. This seems the general rule 10 
the whole class with the many remarkable difference’" 
in structure between the two sexes. We shall he>’^ 
after find the same law prevailing throughout the g 1 ^ 
sub-kingdom of the Vertebrata, and in all cases it 9 
eminently distinctive of characters which have bet ' 11 
11 Claus, 1 Die freilebenden Copepoden,’ 1S63, s. 35. 
