1 899] RE GENERA TION 3 1 3 



the purpose, that appendages are sometimes regenerated, not in the 

 present modern form but, in all probability, on an older type. In 

 fact, reversion to an ancestral type occurs: i.e. the regeneration-" Anlage" 

 has not yet quite reached the same stage as the variation of the part 

 itself. Thus the appendages of Blatta, although growing again satis- 

 factorily, are then, according to Bateson, provided with a four-jointed 

 instead of a five-jointed tarsus, and the same thing has been observed 

 by Bordage in the Phasmidae. Fritz Miiller also records that the long- 

 clawed forceps of a Brazilian shrimp, Atyoida potimirim, is replaced 

 by the older short-fingered type of forceps, similar to that of the allied 

 genus Caridina. Such cases might, of course, be regarded as showing 

 an insufficiency of regenerative power to replace the lost limb perfectly ; 

 but Barfurth has shown that on removal of the four-fingered fore-limb 

 of the axolotl a five-fingered atavistic limb grows in its place. In 

 face of such facts the hypothesis of a general power of regeneration, 

 which restores the damaged " life crystal " to its integrity, is obviously 

 untenable. Here the " crystal " is restored after an older pattern, and 

 one cannot see why this should be so, since the whole has been no 

 more altered than a dodecahedral crystal would be if the point were 

 broken off. If, in that case, the missing portion were suddenly to be 

 re-crystallised on another " system," it could only be because the 

 elements from which the restoration started were, not the remaining 

 whole, but particular parts belonging to another " system," or — to trans- 

 late into the language of biology — because at the injured places there 

 were regeneration-" Anlagen " of earlier origin which came into play as 

 the result of the injury. The existence of " Anlagen " is thereby proved. 

 It has been said that to explain such facts by reversion is to give 

 no explanation at all ; and that such an interpretation, though resulting 

 in ranging the facts under a definite category of phenomena, in no 

 way elucidates the cause which, after the loss of an eye, induces the 

 appearance " of a different type of ancestral-organ. This, however, is 

 just what we want to know " (Herbst). For my own part, I think it 

 is better not to want to know too much all at once. It may be that 

 some day we shall attain to a knowledge of the actual physico-chemical 

 processes which condition development ; but, in the meantime, we are 

 many times the distance to Sirius short of that knowledge, and we 

 shall do well to content ourselves with first striving after nearer goals. 

 Even the simple recognition that we have here to do with a case of 

 atavism — that is, of reversion to an ancestral form — is a creditable 

 piece of knowledge, since it at least enables us to understand why 

 the lost eye of the crab is not replaced by, say, a tuft of feathers, or 

 a monkey's tail. Perhaps, however, the idea here expressed, that the 

 regeneration-" Anlage " lags behind the phyletic transformation of the 

 part itself, may carry us a step farther, always presupposing that we do 

 not regard the principle of Natural Selection as " the greatest error of 

 the century " (Driesch). 



