22 8 Dwellers of the Sea and Shore 



crab has for swimming lies in the leaflike appendages 

 under the abdomen. In this respect its walking legs 

 are very inefllicient, but they are eminently adapted 



_{to the work they chiefly perform; that is, propelling 

 the animal through the sand and mud. If we 

 examine the under side of this quaint creature, a 

 confusing array of appendages confronts us, but a 

 brief though careful inspection will soon familiarize 

 them. Taking first the head region, we find this 

 forms a great cavity, or bowl, in which are contained 

 six pairs of chelate legs (having claws), and one pair 

 of broad horny plates called the operculum. The first 

 pair of legs is small and lies just in front of the mouth. 

 In the male the second pair of claws is larger than in 

 the female. The sixth pair of legs is composed of 

 large, strong segments like the four pairs immediately 

 preceding it, but its claws are of a diminutive size. 

 These latter legs are further peculiar in that they are 

 modified near the ends into a whorl of three flat or 

 oarlike expansions which spread out in use, thus apply- 

 ing greater surface to the yielding sand. The base of 

 this pair of legs has another process termed the 



^ flabellum. With the exception of the first pair, all the 

 legs are set at an angle to the body which enables the 

 animal to bring the greatest power or purchase to bear 

 in forcing its way through the substratum. But there 

 is one extraordinary feature of the legs that will strike 

 the most casual observer; for in no other living animal 

 is there a similar adaptation. Nor for the particular 

 purpose it subserves, is there one quite so singular. 

 Like its ancient forebear, the trilobite, the horseshoe 

 crab carries its teeth on its legs. Excepting the first 



