Crustacea. 7657 



colony as thick as rooks are to be found ranged together ; there the 

 little things sit and pnsh out the head only, and with the long antennae 

 beat the water, keeping guard. These nests in their appearance 

 bear no unstriking resemblance to that of many birds. 



Others, again, change the style of their abodes; instead of secreting 

 threads they make use of mud and clay to perfect the walls, and then 

 secrete a substance that forms a silky lining upon the internal surface. 

 These abodes are generally long and tubular, open at each extremity, 

 and although they are apparently of the diameter suited closely to fit 

 "**the animal, yet they have the power to turn in their abodes. If an- 

 noyed at one extremity, they will turn round and push their heads 

 out of the other. This abode is their place of refuge, and nothing 

 will drive them out but the destruction of their homes. In this way 

 lives the genus Cerapus, which Mr. Say tells us has the power of 

 swimming about with its house on its back, and will crawl amongst 

 the weed, still dragging it after ; not so its near ally, the Siphonoecetus, 

 which anchors its tube to the branches of some zoophyte. 



The habit in these lower forms brings to mind the instinct of the 

 soldier crab, which secures for its convenience the cast-off shells 

 of some mollusk. The species of this genus, when young, bear a 

 near relation to the form of a young lobster. The body of the animal, 

 which is soft and fleshy in the adult, is covered with the integument 

 common to them, traces of which remain in patches even in the adult. 

 During the earlier period the soldier crab swims the surface of the sea 

 in fine weather, but when it grows a little older it seeks a shelter in 

 some convenient shell. These generally they find dead, but some- 

 times they turn out the possessor, making an attack at some con- 

 venient moment, and probably " eat it out of house and home," in the 

 truest meaning of the saying. They no doubt attack and devour 

 mollusks, but the probability is that they do this for the sake of food, 

 and not to obtain the shell in which to reside, but that afterwards, 

 should they want a shell — and they often do change, "just for the fun 

 of the thing " — they may take possession of the one that they had 

 emptied. This statement, probably, holds more true of the older 

 forms, which generally live in the shell of the common whelk, which 

 generally outgrows its abode, so that it is not easy to draw itself into 

 the shell, and therefore falls an easy prey to the burglar crab. Into 

 the shell, when empty, the young crab gets, and, choosing one 

 corresponding in dimensions, occupies it until it outgrows it ; then 

 seeks a fresh and larger shell. We have been told how it rambles 

 along the beach in search of a new habitation, and, having found it, 

 VOL. XIX. 3 A 



