240 



SCIENCE. 



[N. S. Vol. XIV. No. 346. 



generation of the beak of tlie domesticated 

 fighting cocks (of the Malay breed) of Mau- 

 ritius. In the mammals neither the legs 

 nor the tail, nor the jaws regenerate, al- 

 though several of the internal organs, as de- 

 scribed in the next chapter, have extensive 

 powers of regeneration. 



The best opportunity to examine the re- 

 generative power in similar organs of the 

 same animal is found in forms like the 

 Crustacea, myriapods and insects in which 

 external appendages are repeated in each 

 or many segments of the body. In decapod 

 Crustacea, including shrimps, lobsters, cray- 

 fish, crabs, hermit-crabs, etc., regeneration 

 takes place in the walking legs of all the 

 forms that have been examined, and this 

 includes members of many genera and 

 families. I have made a special examina- 

 tion of the regeneration of the appendages 

 of the hermit-crab. In this animal, which 

 lives in an appropriated snail's shell, only 

 the anterior part of the body projects from 

 the shell. The part that protrudes is cov- 

 ered by a hard cuticle, while the part of 

 the body covered by the shell is quite soft. 

 Three pairs of legs are protruded from 

 the shell. The first pair with large claws 

 are used for procuring food, and as or- 

 gans of offense and defense ; the second 

 and third pairs are used for walking. The 

 following two pairs that correspond to the 

 last two pairs of walking legs of crabs 

 and crayfishes, are small, and are used by 

 the animal in bracing itself against the 

 shell. The first three pairs of legs have 

 an arrangement at the base, the ' break- 

 ing-joint,' by means of which the leg is 

 thrown off, if injured. The last two pairs 

 of thoracic legs can not be thrown off. 

 The first three pairs of legs are often lost 

 under natural conditions. In an examina- 

 tion of 188 individuals I found that 21 (or 11 

 per cent.) had lost one or more legs. If 

 one of the first three legs is injured, except 

 in the outer segment, it is thrown off at the 



breaking-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 re- 

 generating these legs under natural con- 

 ditions 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. More- 

 over, the new leg is perfect in every re- 

 spect, even to the formation of a new 

 breaking-joint. In this case we have a 

 demonstration that there need be no con- 

 nection 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 anesthe- 

 tized, 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 some- 

 times 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 can not be thrown off, but they have 

 the power of regeneration at any level at 

 which they may be cut off. They are in a 



