CRUSTACEA. 509 



of La Rochelle they are useful friends to the oyster by destroying 

 these enemies, although they do not hesitate to attack the mollusc 

 when it comes in their way. During the winter the mud of the 

 bouchots gets piled up in unequal heaps, and when the warm season 

 returns it has become hard and unfit for the cultivation of the 

 mollusc. It is necessary to level and dry these mud-heaps a process 

 which would be both difficult and costly. Well, the Corophii charge 

 themselves with the task. They plough up annually many square 

 leagues covered with these heaps. They dilute the mud, which is 

 carried out by the ebbing tide, and the surface of the bay is left 

 smooth, as it was in the preceding autumn. 



We have said that the Crustaceans do not even respect each other ; 

 the larger of the same species often devour the smaller. Rara con- 

 cordiafratrum ! Mr. Rymer Jones relates that he had on one occa- 

 sion introduced six crabs (Platycarcinus pagurus) of different sizes into 

 an aquarium. One of them, venturing towards the middle of the 

 reservoir, was immediately accosted by another a little larger, which 

 took it with its claws as it might have taken a biscuit, and set about 

 breaking its shell, and so found a way to its flesh. It dug its crooked 

 claws into it with voluptuous enjoyment, appearing to pay no attention 

 to the anger and jealousy of another of its companions, which was 

 still stronger and as cruel, and was advancing upon it. But, as 

 Horace says and he was not the first to say it " There is nothing 

 altogether happy" 



"Nihil est ab omni parte beatum." 



Our ferocious Crustacean quietly continued its repast, when its com- 

 panion seized it exactly as it had seized its prey, broke and tore it in 

 the same fashion, penetrating to its middle, and tearing out its entrails 

 in the same savage manner. In the meantime the victim, singularly 

 enough, did not disturb itself for an instant, but continued to eat the 

 first crab bit by bit, until it was itself entirely torn to pieces by its 

 own executioner a remarkable instance at once of insensibility to 

 pain and of cruel infliction under the lex talionis. To eat and to be 

 eaten seems to be one of the great laws of Nature. 



Though essentially carnivorous, the Crustaceans sometimes feed 

 on vegetable food. Many even seem to prefer fruit to animal food. 

 Such is the robber-crab (Birgus latrd) of the Polynesian Isles, which 

 feeds almost exclusively on the cocoa-nut. This crab has one thick 

 and strong claw ; the others are comparatively slender and weak. At 

 first glance it seems impossible that it could penetrate a thick cocoa- 

 nut surrounded by a thick bed of fibre and protected by its strong 



