AN ABERRANT LIMB IN A CRAY-FISH. 83 



mode of formation of such structures. The appearance of the 

 limb suggests a new growth following some injury in which the 

 material for claw making was partly severed and displaced. 

 This might happen, we can suppose, not only in the egg and in 

 the young, but in the adult, especially at the periods of shedding 

 when the interior of the claw is soft and the blood peculiar. 

 That limbs may regenerate from a peripheral wound was shown 

 by Herrick for the tips of the claws and by Morgan l for large 

 parts of the limb. Possibly then such a monstrosity as this 

 might arise in regeneration following an injury to the propodite. 

 An attempt to get experimental evidence resulted in failure, 

 but this is what would be expected from the rarity of such mon- 

 strosities and from the difficulties in keeping the material long 

 enough. In that attempt 103 mature Canibanis affinis were oper- 

 ated on in February. In each a deep cut was made in the 

 carpodite of each chelate walking leg at a point corresponding to 

 the pronged structure in this abnormal limb. In ten days many 

 had healed, some could again use the dactyl and some had 

 dropped the parts peripheral to the cut. Subsequently a piece 

 was removed where the cut had been made in order to prevent 

 such rapid healing. The breeding season then came on and 

 after some months all the specimens had died without shedding 

 and no new formations were found. 



1 Morgan, " Regeneration of the Appendages of the Hermit Crab and Crayfish," 

 Anat. Anz., XX., 1902. 



