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 * Nature ' (xv., p. 415) there is a notice of a lobster 

 (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 

 ' mounted guard.' ' 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 * 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 * 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 



