REGENERATION AND LIABILITY TO INJURY 99 



ing-joint, and a new leg regenerates from the broken-off end of the 

 stump that is left. The new leg does not become full size, and is of 

 little use until the crab has moulted at least once. The leg breaks 

 off so close to the body, and the part inside of the breaking-joint is 

 so well protected by the bases of the other legs, that it is scarcely 

 possible that the leg could be torn off inside of the breaking-joint, 

 and, as a matter of observation, all crabs that are found regenerating 

 their legs under natural conditions do so from the breaking-joint. 

 If, however, by means of small scissors, the leg is cut off quite near 

 the body, a new leg regenerates from the cut-end, even when the leg 

 is cut off at its very base. The breaking-joint would thoroughly pro- 

 tect from injury the part of the leg that lies nearer to the body, and 

 yet from this inner part a new leg is regenerated. Moreover, the 

 new leg is perfect in every respect, even to the formation of a new 

 breaking-joint. In this case we have a demonstration that there need 

 be no connection between the liability of a part to injury and its 

 power of regeneration. 



In still another way the same thing may be shown. If the crab 

 is anaesthetized, and a leg cut off outside of the breaking-joint, it is 

 not, at the time, thrown off the nervous system, through whose 

 action the breaking off takes place, being temporarily thrown out 

 of order. After recovery, although the leg is thrown off in a large 

 number of cases, it is sometimes retained. In such cases it is found 

 that from the cut-end the missing part is regenerated. In this case 

 also we find that regeneration takes place from a part of the leg that 

 can never regenerate under natural circumstances. 



The third and fourth legs of the hermit-crab cannot be thrown 

 off, but they have the power of regeneration at any level at which 

 they may be cut off. They are in a position where they can seldom 

 be injured, and I have never found them absent or injured in crabs 

 caught in their natural environment. The soft abdomen is protected 

 by the snail's shell. At the end .of the abdomen the last pair of 

 abdominal appendages serve as anchors to hold the crab in the shell. 

 These appendages are large and very hard, and can seldom be in- 

 jured unless the abdomen itself is broken, and under these circum- 

 stances the crab dies. Yet if these appendages are cut off they 

 regenerate perfectly, and after a single moult cannot be distinguished 

 from normal ones. 



The more anterior abdominal appendages are present only on one 

 side of the adult, although they are present on both sides of the larva, 

 and, to judge from a comparison with other Crustacea, these append- 

 ages have degenerated completely on one side, and have become 

 rudimentary in the male, even on the side on which they are present. 

 They too will regenerate if they are cut off. In the female these 



