92 THE LIFE OF CRUSTACEA 



activity quite foreign to the nature of their original 

 molluscan inhabitants, and closer examination will 

 show that each contains a Hermit Crab, which 

 retreats into the shell when disturbed. If extracted 

 from the shell, the Crab (Fig. 36) can be seen to be 

 most beautifully adapted to its peculiar mode of life. 

 The abdomen is soft and spirally twisted to fit into 

 the interior of the spiral shell, and the uropods, 

 instead of forming a tail-fan, are modified into 

 holding organs, with roughened, file-like surfaces 

 which can be pressed outwards against the walls of 

 the shell, and wedge the body so firmly that an 

 attempt to drag the animal forcibly from its retreat 

 often results in tearing it in half. The front part of 

 the body, which is exposed when the animal is 

 walking, retains its shelly armour. One of the 

 pincer-claws, most commonly the right, is much 

 larger than the other, and serves to block the open- 

 ing of the shell when the body is withdrawn into it. 

 The next two pairs of legs are long and slender, and 

 are used for walking ; but the last two pairs are 

 short, with a roughened surface at the end, and 

 serve to steady the body in the mouth of the shell. 

 The swimmerets on the right side of the body, 

 which is pressed against the central pillar of the 

 shell, have disappeared, but those of the left side 

 remain. 



As the Hermit grows, it is necessary for him to 

 remove from time to time into a larger dwelling. 



