MARINE ARTHROPODS 283 



the shell has already been secured by the clinging petals of this 

 dangerous marine flower, the hermit will speedily quit its home 

 and endeavour to rush from the many snares in order to secure its 

 freedom. Orj it not infrequently happens that the occupied shell is 

 one that has withstood many a storm, but not without the loss of 

 the apex of its cone. In this case the insertion of a very flexible 

 fibre into the opening thus made will cause the hermit to leave its 

 home in the possession of the enemy. 



Having, by some means or other, managed to drive the crab 

 from its shell, we place it in a shallow rock pool, or in a vessel of 

 sea water, and observe the chief features of its structure. 



The first thing that strikes one is the absence of a calcified skin 

 on the extended abdomen, which is so soft that, remembering with 

 what eagerness fishes will attack and devour crabs of all kinds, we 

 can at once understand the necessity of such a home as the creature 

 selects. Again, we observe the presence of appendages at the tip 

 of the abdomen by means of which the crab is enabled to hold 

 itself securely in the shell. Also, when we note the general form 

 of the armoured portion of the body, and the position of the soft- 

 skinned abdomen, we can see how well adapted the whole is to fit 

 snugly into the spiral shell of a whelk or winkle. 



We also observe that one of the pincers is much larger than the 

 other, and the value of such an arrangement may be estimated 

 when we see the animal at home. The smaller claw, together 

 with the other appendages used for walking or prehension, can be 

 retracted within the shell, but the large claw, which constitutes a 

 formidable weapon of attack and defence, is not only in such a 

 position as to be ready for immediate use ; but, lying as it does in 

 front of the body, with other portions hidden more or less behind 

 it, it serves the purpose of a shield when the animal retires. 



If we place a homeless hermit crab in a rock pool, the be- 

 haviour of the creature immediately suggests a feeling of uneasi- 

 ness a sense of danger for it moves about in a very erratic fashion 

 that is quite different from the straightforward and deliberate action 

 of the same animal when properly protected ; and very amusing 

 results may be obtained by making it the subject of a few harmless 

 experiments. For instance, drop down before it an empty whelk- 

 shell that is much too large to properly accommodate its body. It 

 will immediately approach the untenanted house, search and probe 

 it well with its antennae and other appendages, and then, finding it 

 uninhabited, and having no apartment of more suitable size at 



