33-1 SEXUAL SELECTION. Part IL 
“ was a bloodless one, for I saw no wounds.” This 
same naturalist separated a male sand-skipper (so com- 
mon on our sea-shores), Gammarus marinus, from its 
female, both of which were imprisoned in the same 
vessel with many individuals of the same species. The 
female being thus divorced joined her comrades. After 
an interval the male was again put into the same 
vessel and he then, after swimming about for a time, 
dashed into the crowd, and without any fighting at once 
took away his wife. This fact shews that in the Amphi- 
poda, an order low in the scale, the males and females 
recognise each other, and are mutually attached. 
The mental powers of the Crustacea are probably 
higher than might have been expected. Any one who 
has tried to catch one of the shore-crabs, so numerous 
on many tropical coasts, will have perceived how wary 
and alert they are. There is a large crab (Birgos 
Icitro), found on coral islands, which makes at the 
bottom of a deep burrow a thick bed of the picked 
fibres of the cocoa-nut. It feeds on the fallen fruit of 
this tree by tearing off the husk, fibre by fibre ; and 
it always begins at that end where the three eye- 
like depressions are situated. It then breaks through 
one of these eyes by hammering with its heavy front 
pincers, and turning round, extracts the albuminous 
core with its narrow posterior pincers. But these actions 
are probably instinctive, so that they would be per- 
formed as well by a young as by an old animal. 
The following case, however, can hardly be so con- 
sidered : a trustworthy naturalist, Mr. Gardner , 9 whilst 
watching a shore-crab (Gelasimus) making its burrow, 
9 ‘Travels in the Interior of Brazil/ 1846, p. 111. I have given, in 
my 1 Journal of Researches/ p. 463, an account of the habits of the 
Birgos. 
