258 



CRUSTACEANS. 



The second family (Ocypodidce) is typically represented by the swift land- 

 crabs (Ocypoda), which appear to be less strictly terrestrial than the last, although 

 unable to endure a long sojourn in the sea. Indeed, from the adoption of a land 

 life their breathing-organs have become so modified that these crabs may be drowned 



swift land-crab (nat. size). 



by an immersion of twenty-four hours. They frequent sandy beaches, and when 

 chased run with such speed, as to make their capture a matter of difficulty. 

 They burrow deep perpendicular holes in the sand. In these they stay when 

 the tide is up, but at low water they wander over the beach in search of food, 

 which consists of sand-hoppers or any offal cast up by the waves. 



These crabs are gregarious, in the sense that numbers frequent the same spot. 

 Each has a burrow to itself, and if one of them tries to enter by mistake the 

 burrow of another, the rightful occupant makes a loud scraping noise to warn the 

 intruder of its error ; whereupon the latter retreats in search of its own abode. 

 So strong is this instinct against trespassing, that a crab will always risk the 

 chance of a fresh run for safety, rather than persevere in seeking concealment in 

 the home of another. 



Nearly allied to the foregoing are the calling-crabs (Gelasimus), represented by 

 a number of species from the warmer parts of the world. The carapace is broad 

 ^^^ and squared in front, and the long slender eye- 



stalks lie when at rest along its front border, 

 sunk in the orbits. But the most remarkable 

 characteristic is the enormous size of one of the 

 pincers in the male ; and it is from the habit of 

 brandishing this claw, as if beckoning, that the 

 name of calling-crab is derived. So abundant 

 are these crabs, that they may frequently be 

 seen by the thousands either running over the 

 sand or peering out of their holes. These holes, 

 which are thickly scattered over wide areas, lead into burrows frequently a foot 

 or more in depth. The crabs scrape up a heap of sand, and grasping the pellet 

 with three of the legs of one side, carry it to some distance before letting it 



calling-crab (nat. size). 



