SCORPIONS, SPIDERS AND CRABS 255 



been confined to such as, during adult life, at least, are 

 land-dwellers. But the aquatic types known as the 

 " Crustacea '' furnish some extremely interesting facts 

 in regard to the problems of sex. In the first place, they 

 too possess a stridulating apparatus. This is curious, 

 but not surprising, because, although the skeleton of 

 such creatures is of a harder and almost stone-like 

 character, the development of roughened surfaces work- 

 ing in opposition to one another might well have been 

 foretold to occur, at least in some individuals. Colonel 

 Alcock — a naturahst who has contributed largely to our 

 knowledge of marine animals by his researches in the 

 Indian Ocean — in his most delightful book " A Naturahst 

 in Indian Seas," describes what he calls a " musical 

 crab." This is the great-horned Coromandel Strand Crab 

 {Ocypoda macrocerd). In both sexes of this remarkable 

 genus he says, " the nippers, or chelipeds, are singularly 

 unequal in size, and in all the species but one there is 

 present on the inner surface of the ' hand ' of the larger 

 cheliped a transverse row of five teeth, which, when 

 the cheliped is flexed, can be made to play against a 

 ridge or another row of teeth on its * arm ' . . . much 

 as a man might rub one side of his chest with the palm 

 of the corresponding hand. The whole mechanism, 

 except that it is on a larger scale and has a more finished 

 appearance, is very much like that by means of which 

 crickets and grasshoppers produce their shrill music, 

 and no one has ever doubted that it is used for the same 

 purpose, though very few people have actually heard 

 it in action. I myself . . . was beginning to think that 

 the structure must, after all, have some quite other 

 function, when one morning ... on the sandy wastes 

 of the Godavari delta, I at last, like Ancient Pistol, heard 



