MARINE ARTHROPODS 259 



cast skin without considerable injury to the new claw that is already 

 formed, though as yet in a soft condition, within the old and hard 

 one. But it has been observed that this plate actually cuts through 

 the new claw, and that the claw thus divided almost immediately 

 closes up and unites again. 



The moulting process being over, the crustacean's body extends 

 itself within the new, yielding skin; and, the latter becoming 

 gradually hard by tbe deposition of carbonate of lime, the creature 

 is able, after a period of rest, to roam at large again, without much 

 fear of injury, until the time for the next moulting has arrived. 



Those who have made but a slight acquaintance with the 

 common crustaceans of our shores must have noted the frequency 

 with which imperfect specimens occur specimens with missing 

 appendages, or with a well-formed limb on one side of the body 

 opposed to a puny and almost useless fellow on the opposite side. 

 As to the loss of appendages, this matter will be readily understood 

 by those who have watched crustaceans, arid especially crabs and 

 lobsters, in their native element, so often do these pugnacious 

 creatures become engaged in furious broils with their neighbours. 

 And, when we are at work at the collection of various species on the 

 sea shore, how often do we find that a creature escapes from our 

 grip by leaving us in possession of a severed limb, while the owner 

 retreats rapidly among the stones and weeds apparently none the 

 worse for its trifling loss ! This is, in fact, a very common method 

 of securing its escape from an enemy ; and it appears that many 

 crustaceans have the power of thus rendering a seized limb so brittle 

 that it may be snapped off with the greatest of ease. 



We have spoken of the loss thus sustained as a trifling one ; 

 and so it is, for crustaceans have the faculty of reproducing lost 

 appendages; and though the loss may be one of considerable 

 inconvenience at first, a new limb eventually appears in the place of 

 each one so willingly discarded. 



When such mutilations occur, it will be observed that the 

 severed limb invariably breaks away at the end of the first or 

 basal joint a point where the bloodvessels are so narrow and 

 contractile that but little loss of blood takes place when the 

 rupture is made and it has been said that the animal would soon 

 bleed to death if the fracture were to take place at any other point. 

 As it is, the wound soon heals, but no trace of a new limb is to be 

 seen, at least without dissection, until the time of the next moult. 

 The part is developing, however, beneath the cover of the basal 



