CRABS AND LOBSTERS. 
233 
sentinel an unmoultcd or hard-shelled individual, to 
prevent marine enemies from injuring moulted individuals 
in their unprotected state. While thus mounting guard 
the hard-shelled crab is much more courageous than at 
other times, when he has only his own safety to consider. 
But these observations require to be corroborated. 
In 6 Nature ’ (xv., p. 415) there is a notice of a lobstei 
(Homarus marinus ) in the Rothesay Aquarium which 
attacked a flounder that was confined in the same tank 
with him, and having devoured a portion of his victim, 
buried the rest beneath a heap of shingle, on which he 
6 mounted guard.’ 6 Five times within two hours was the 
fish unearthed, and as often did the lobster shovel the 
gravel over it with his huge claws, each time ascending 
the pile and turning his bold defensive front to his com- 
panions.’ 
The following is quoted from Mr. Darwin’s 6 Descent of 
Man ’ (pp. 270-1): — 
A trustworthy naturalist, Mr. Gardner, whilst watching a 
shore-crab ( Gelasimus ) making its burrow, threw some shells 
towards the hole. One rolled in, and three other shells re- 
mained within a few inches of the mouth. In about five 
minutes the crab brought out the shell which had fallen in, and 
carried it away to the distance of a foot ; it then saw the three 
other shells lying near, and evidently thinking that they might 
likewise roll in, carried them to the spot where it had laid the 
first. It would, I think, be difficult to distinguish this act 
from one performed by man by the aid of reason. 
Mr. Darwin also alludes to the curious instinctive 
habits of the large shore-crab ( Birgus latro\ which feeds 
on fallen cocoa-nuts 6 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.’ 
Remarkable cases occur of commensalism between 
certain crabs and sea-anemones, and they betoken much 
intelligence. Thus Professor Mobius says in his ‘ Beitrage 
zur Meeresfauna der Insel Mauritius’ (1880) that there 
are two crabs belonging to different genera which have 
