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. Rava con- 
cordia fratrum! 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 toits 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 Zex ¢alionis. To eat and to be 
eaten seems to be one of the great laws of Nature. —, 
Thoughessentially carnivorous, the Crustaceans sometimes feed 
on vegetable food. Many even seem to prefer fruit to animal food. 
Such is the robber-crab (Birgus Jatro) of the Polynesian Isles, which 
feeds almost exclusively on the cocoanut. 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 
