Ill] OF REGENERATION 279 



If we amputate a claw, or if, as often happens, the crab "casts 

 it off," it undergoes a process of regeneration — it grows anew, 

 and does so with an accelerated velocity which ceases when 

 equilibrium of the parts is once more attained : the accelerated velocity 

 being a case in point to illustrate that vis revulsionis of Haller to 

 which we have already referred. 



With the help of this principle, Przibram accounts for certain 

 curious phenomena which accompany the process of regeneration. 

 As his experiments and those of Morgan shew, if the large or knobby 

 claw (A) be removed, there are certain cases, e.g. the common 

 lobster, where it is directly regenerated. In other cases, e.g. 

 Alpheus*, the other claw (B) assumes the size and form of that 

 which was amputated, while the latter regenerates itself in the 

 form of the lesser and weaker one; A and B have apparently 

 changed places. In a third case, as in the hermit-crabs, the A- 

 claw regenerates itself as a small or 5-claw, but the 5-claw 

 remains for a time unaltered, though slowly and in the course of 

 repeated moults it later on assumes the large and heavily toothed 

 ^-form. 



Much has been written on this phenomenon, but in essence it is 

 very simple. It depends upon the respective rates of growth, upon 

 a ratio between the rate of regeneration and the rate of growth of 

 the uninjured limb: that is to say, on the familiar phenomenon of 

 unequal growth, or, as it has been called, heterogony*. It is com- 

 plicated a little, however, by the possibility of the uninjured limb 

 growing all the faster for a time after the animal has been relieved 

 of the other. From the time of amputation, say of A, A begins to 

 grow from zero, with a high "regenerative" velocity; while B, 

 starting from a definite magnitude, continues to increase with its 

 normal or perhaps somewhat accelerated velocity. The ratio 

 between the two velocities of growth will determine whether, by a 

 given time, A has equalled, outstripped, or still fallen short of the 

 magnitude of B. 



That this is the gist of the whole problem is confirmed (if con- 

 firmation be necessary) by certain experiments of Wilson's. It is 



* E.' B. Wilson, Reversal of symmetry in Alpheus heterocheles, Biol. Bull, iv, 

 p. 197, 1903. 

 t See p. 205. 



