68 THE OCEAN. 
appearance crawling under the perpetual shadow of 
its own tree, the burden of whose weight, however, 
was probably more than compensated by the pro- 
tection it afforded against enemies. 
A singular little creature, called the Hermit Crab 
(Pagurus), the hinder part of whose body is unpro- 
tected, except by a soft skin, is endowed with an 
‘instinct which prompts it to seek some univalve 
shells, into which it thrusts its abdomen, henceforth 
using it as a house. Now there is a species of 
Sponge found on our coast (7. suberea), of a corky 
substance, which grows on the surface of similar 
shells, overspreading and enveloping them; and it 
so happens that in the great majority of instances, 
the Sponge is found upon the individual shells in- 
habited by the Hermit. Gradually and insensibly 
the Sponge grows over the shell, and at length creeps 
round the edge of the lip, and begins to line the 
inside: the constant motion of the crab, who is very 
active, retards the growth for a while, but eventually 
the Sponge prevails, and the Hermit, finding his pre- 
mises becoming every day more and more contracted, 
is at length compelled to seek another lodging. A 
proceeding very similar to this, but which the Her- 
mit Crab finds rather, to his advantage than discom- 
fort, takes place in the growth of a species of Coral 
(Aleyonium echinatum). This coral also very fre- 
quently grows on a shell selected for a habitation 
by the little crab; but as it grows, it does not line 
the shell, but becomes moulded, as it were, to the 
form of the enclosed animal, thus increasing the size 
and commodiousness of the dwelling, and precluding 
