48 ADAPTATION OF STEUCTUEE TO HABIT. 



bottom may be very narrow, and I am not sure but that 

 the Crab likes it all the better, for he is expressly 

 formed for such a dwelling ; his body is particularly 

 flat, his legs move in the same plane, and his claws, 

 though large for his size, are remarkably flat also, 

 thinned out, as it were, to an edge ; so that the whole 

 animal has somewhat the appearance of having been 

 crushed flat by the pressure of the stone under which 

 he lives. Here then is a beautiful adaptation of 

 structure to habit ; but there is more of the same kind. 

 The Crabs are carnivorous, and in general they are 

 very active, wandering continually in search of prey, 

 which they seize when observed with their claws. 

 How is our little Broad-claw to live, clinging fast to 

 his cranny, which he forsakes not from one month's 

 end to another. Like the thrifty housewives of 

 London, who do not go to market, but have their 

 bread and meat and groceries brought to their door. 

 Let us see how this is managed. Professor Bell 

 in his beautiful " History of British Crustacea," thus 

 alludes to one character of this genus. " External 

 pedipalps greatly developed ; the second joint very 

 large, rounded, with a single tooth on the outer 

 anterior angle ; the third joint much smaller, irregu- 

 larly trigonal, and with the remaining joints fringed 

 with long hair at the edges." In fact, however, all 

 these joints are fringed with hair, which curves in- 

 wards, but its use in the economy of the animal 

 has not yet, so far as I am aware, been made known. 

 Watching a Broad-claw beneath a stone close to 

 the side of my tank, I noticed that his long antennas 

 were continually flirted about ; these are doubtless 



