314 AUGUST WE ISM ANN [apbil 



Let us now return to Morgan's results with the hermit-crab, in 

 order to attempt an explanation of the fact that all the appendages of 

 this animal have remained capable of regeneration — even those which 

 are protected by the shell in which it lives, as well as the abdominal 

 appendages of the male, which are presumably rudimentary and have 

 no function to fulfil. 



The cause of this seems to me to be the same as in the case I 

 have just discussed, viz. the lagging of the regeneration-" Anlage " 

 behind the progressive transformation of the limb — -the fact that 

 variation, even if it be retrogressive, goes on much more slowly in the 

 regeneration-" Anlage " than in the limb itself. The predisposition to 

 regeneration is useless in the case of limbs which are completely con- 

 cealed and therefore not liable to injury, as well as in the case of non- 

 functional appendages : but it cannot be in any way harmful, and 

 therefore will not be gradually got rid of by an active negative process 

 of selection — as are the abdominal appendages on the right side which 

 are directed towards the axis of the spiral shell— but by that slow 

 process of disappearance of parts which have become useless but are 

 not harmful, which I refer to the operation of germinal selection under 

 the influence of Panmixia. I hope to discuss this process more fully 

 elsewhere, and, for our present purpose, it is not essential to have 

 before us a clear theoretical statement of the gradual degeneration of 

 useless parts and of the regeneration-" Anlagen." If it be certain that 

 this gradual down-sinking and degeneration takes place xoitli extreme 

 sloivncss, we need not wonder that the predisposition to regeneration, 

 which was for ages indispensable to the life of the animals, should still 

 persist long after it has become useless and superfluous. From a 

 phylogenetic point of view, we are justified in saying that the whole 

 group of hermit-crabs came into existence only recently, that is, since 

 the end of the Cretaceous period. In any case, we know that a species 

 of Urodele {Proteus) has lived an incomparably longer time in the 

 caves of Krain, and we need not wonder that in this hermitage it has 

 lost the power of regeneration in limbs and tail, while the hermit-crabs 

 still possess it in their abdominal appendages. 



There is yet another group of phenomena which stamp the power 

 of regeneration as an adaptation on the basis of inherited preliminary 

 conditions, viz. the self-amputation of limbs, a process which has 

 repeatedly been studied of late years. This was described by M'Culloch 

 in 1826, later by Goodsir, and in recent years by Fr^dericq and others. 

 Bordage has also written about the so-called " autotomy " of leaf-insects 

 (Phasmidae), in regard to which he established the fact, mentioned 

 above, that young specimens of Monandroptera inuncans renew the 

 tarsi after amputation with only four joints instead of five. Bordage 1 

 has taken advantage of his recent sojourn on the island of Pieunion to 



1 " Sur les localisations des surfaces de regeneration chez les Phasmides," Compt. Rend. 

 Soc. Biol. Paris, 1S98. 



