72 Part second. 



itself entirely from view in case of danger. As it grows, it must from 

 time to time change its dwelling, when the latter becomes too small; 

 and this it does with great circumspection. When it has found a shell 

 suitable for its purpose, it first examines it carefully all over, poking 

 its claws far into the cavity so as to make sure that there is nothing 

 suspicious lurking within it; then, if all is right, it cautiously prepares 

 to effect the removal. It gets hold of the shell with its claws, places 

 it in an upright position with the opening toward itself, and with one 

 quick dart forsakes its old shell, and slips into the new one, as if it 

 well knew what a tit-bit its soft juicy body would be for a hungry fish. 



But why should often three or even six Sea-anemones be so re- 

 gularly attached to the shell occupied by the Hermit-crab, and yet be in 

 no way organically connected with the crab? It is evidently a friendly 

 alliance which has sprung from some mutual advantage gained; this 

 consists, so far as we can see, in the Hermit-crab being protected by 

 the poisonous stinging-cells of the Anemone (see p. 56), so that its ene- 

 mies (turtles and cuttle-fish) are kept at bay by the pain they experience. 

 The Anemones, on the other hand, have a greater chance of finding 

 food; as they need not wait, like those fixed to a rock, till the food 

 comes within their reach , but are constantly brought into contact with 

 all kinds of animals by the vagabond life of the crab, and may occasion- 

 ally catch some bits of the crab's own meal. This is the case with the 

 beautifully purple-spotted Anemone Adamsia palliata (Fig. 166), which 

 is always fixed to shells inhabited by the Eupagurus Prideauxii , and 

 is so placed that it can catch what falls from the lips of the crab. But 

 the most wonderful thing is that the crab knows its friend, and not 

 only tries to put anemones on shells which are devoid of them, but 

 actually takes its companions along with it, when it changes its house! 

 Observations and experiments have placed this beyond all doubt, and 

 prove this alliance to be one of the most remarkable known among lower 

 animals. 



The life of the Hermit-crabs in the Aquarium is rich in varied and 

 amusing scenes. The droll fights of the little troop, the way they tumble 

 about, flee and follow each other up , the impudent seizures of some 

 and resolute defence of the others during the common meal invariably 

 excite the laughter of the spectator, who is often greatly surprised at 

 the artful and calculating ways of the little creatures. In these habits 

 the Hermit-crabs rank next to the true Crabs , to which we will now 

 turn our attention. 



In the Hermit-crabs we noticed a retrogression in the rudimentary 

 development of the tail, brought about by their mode of life. In the 

 short-tailed Crabs (Brachyura) this retrogression has gone still further, 

 but has been accompanied by an increase in agility. Here the large 

 portion of the body which forms the tail of the lobster, is reduced to 

 a small round or triangular plate which is doubled up under the stomach- 

 region and is therefore not seen from above. The anterior part of the 

 body is laterally expanded and is mostly of a roughly triangular or 

 square shape; the well known Shore-crab may serve as a type. 



To begin with, we would mention the Crabs with a triangular 



