CHAPTER XXVII 



THE LITTOEAL AND MARINE FAUNA' 



There is another group of settlers in the atoll which has 

 neither come by flying nor by chance flotsam in the ocean drifts, 

 and this is the large army of crabs that has invaded the 

 land so successfully. The crabs of the atoll show a series of 

 transitions between those forms that live entirely in the waters 

 around the group and those that, living always on the land, 

 seek, so far as I have observed, those parts of the islands 

 farthest removed from their ancestral home. 



Around the sandy beaches of the lagoon live several species 

 of the genus Ocypoda, and they are interesting and rather 

 beautiful crabs of . a pale olive-grey colour, and of excessively 

 active habits. They run sideways on the extremities of their 

 long legs, and their two wonderful eyes are held above them 

 as watch-towers, for ever turning this way and that as danger 

 threatens. These crabs live in spiral burrows along the sandy 

 margins of the lagoon, and digging one out of his burrow 

 is a rather difficult proceeding, for the holes are deep and 

 winding. Concerning the spiral nature of the burrows a 

 point of interest arises, for is it always possible to tell from 

 without which way the spiral is wound within. At the 

 mouth of each burrow is a little shoot of sand, cast out by the 

 crab in his excavations ; at times the sand-heap is to the 

 right, and at times to the left of the hole, and the tailing out 

 of the shoot leads to the hole in a curve which commences the 

 spiral of the whole boring. 



There is no mere chance concerning the winding of these 

 tunnels, for the right-handedness or left-handedness of their 

 spiral depends upon which of the cheln3 of the individual is 

 the most developed. If the crabs are watched, it will be 



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