STRAND CRABS 213 



flats with those of the smaller fiddler-crab (Gelasiimis 

 anmilipes). Both these crabs are amphibious, living in 

 fact more on dry land than in the sea, and both are 

 remarkable for their activity and intelligence : indeed, 

 after much observation of them, I am inclined to think 

 that the crabs of these two genera are about the most 

 gifted members of the whole crustacean class, and 

 among Arthropods are inferior to none but the social 

 insects. Though they have seven pairs of gills, which 

 are well developed and functional, yet the gills do not 

 nearly fill the enormous gill-chambers, and it is mainly 

 by means of these capacious gill-chambers and by the 

 thick and vascular membrane which lines them that 

 Ocypoda and Gelasimus are able to breathe on dry land : 

 a special air-slit, which opens between the bases of the 

 second and third pairs of running legs and is well 

 protected by a thick filter of hairs, allows air to enter 

 and leave the gill-chambers. 



In the adults of all but one of the species of Ocypoda 

 the eye-stalks are produced beyond the eye itself, to form 

 a pair of long slender horns, and these are particularly 

 conspicuous in O. macrocera. What the use of these 

 horns may be we do not exactly know, but it is possible 

 that they may serve as organs of touch, seeing that 

 the antennae are rudimentary in this genus. Again, in 

 both sexes of this remarkable genus the nippers, or 

 chelipeds, are singularly unequal in size, and in all the 

 species but one there is present on the inner surface 



