Tank Nr. 23. 
41 
one suitable for its size, it puts its tail into it; but if it does not, it first 
eats out the whelk and then takes possession of the shell. In the course 
of many generations the hind portion of the body has become so accustomed 
to a borrowed covering, that it is quite soft, and resembles an unjointed sack 
(Fig. 61) possessing at its extremity a pair of rudimentary legs; with 
these it holds so fast to the shell that in trying to extricate the animal you 
may very often tear it to pieces. The shell thus serves as a protection, and 
is usually so large, that the Hermit-crab can withdraw 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 open¬ 
ing towards itself, and with one quick dart forsakes its old shell, and 
Fig. 61. Pagurus striatus , V 2 nat. size. Fig. 62. Eupagurus Prideauxii in a 
Tank 23. shell and bearing the Anemone 
Adamsiapalliata, 1 / 2 na t*size. Tank23. 
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 ar 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. 15), so that its enemies 
(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 occasionally catch 
some bits of the crab’s own meal. This is the case with the beautifully 
purple-spotted Anemone Adamsia palliata (Fig. 62), 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 
