MARINE CRUSTACEANS. 259 



and in the water, but half concealed beneath the 

 overhanging fronds, a large crab of the edible 

 species usually brought to market, another kind 

 usually found in rock pools, and two or three 

 hermit-crabs, whose claws are protruded from the 

 mouths of the shells in which they have taken up 

 their abode. Then there are several shrimps, 

 which, terrified by our visit, have darted off, and 

 are busily engaged burying themselves in the 

 sand, on which their semi-transparent bodies 

 would be almost effectually concealed without 

 the process of sinking into the surface. Leaving 

 such of the molluscs as we thus discover to be 

 studied on some future ramble, we shall pay our 

 respects to our hermit and his relations. 



According to the most eminent naturalists, the 

 essential character of the class Crustacea is the 

 combination of branchiae, or breathing apparatus, 

 with jointed limbs and distinct sexes. "The 

 name of this class refers," as Professor Owen ob- 

 serves, " to the modification of the external tegu- 

 ment by which it acquires due hardness for pro- 

 tecting the rock-dwelling marine species from the 

 concussion of the surrounding elements, from the 

 attacks of enemies, and likewise for forming the 

 levers and points of resistance in the act of sup- 

 porting the body and moving along the firm 

 ground. In the crab and lobster tribes the in- 

 ternal layer of the integument is hardened by the 

 addition of earthy particles, consisting of the car- 

 bonate with a small proportion of the phosphate 

 of lime." 



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