82 PROBLEMS OF GENETICS 



will. All we know is that it can "remain itself" when much is 

 removed, and when much rearrangement has been affected, 

 which is a different thing altogether. 



I scarcely like to venture into a region of which my ignorance 

 is so profound, but remembering the powers of eddies to re-form 

 after partial obliteration or disturbance, I almost wonder whether 

 they are not essentially machines which remain themselves 

 when parts of them are removed. 



Real progress in this most obscure province is not likely to be 

 made till it attracts the attention of physicists ; and though they 

 for long may have to forego the application of exact quantitative 

 methods, I confidently anticipate that careful comparison 

 between the phenomena of repetition formed in living organisms 

 and the various kinds of segmentation produced by mechanical 

 agencies would be productive of illuminating discoveries. 14 



14 The conclusion expressed (p. 72) that the extra appendages of Arthropods 

 result from injury, may have to be modified in view of the remarkable evidence 

 lately obtained by Miss Hoge {Jour. Exp. Zool., 1915, xviii, p. 241) showing that 

 in Drosophila the production of extra paired legs is a Mendelian character behav- 

 ing as a recessive of a peculiar kind, easily modified by temperature. The case of 

 the Prionus {Materials, p. 544) found with all six legs bearing extra parts had 

 always seemed to me inconsistent with the suggestion that injury was the exciting 

 cause, especially since in a second specimen of Prionus two legs had been found 

 thus affected. Nevertheless here, and even in the Drosophila strain, it might 

 be argued that the essential distinction may consist in a natural liability to 

 autotomy at some developmental stage, the extra growths being produced in con- 

 sequence of this. 



