A DYNAMICAL HYPOTHESIS OF INHERITANCE. 43 



rated by mechanical or other means, also cause changes to be 

 produced in the forms of the single larvae of such coherent 

 groups, and in the spicular skeleton, for the same reason, as 

 is proved by Figs. 23 to 25 given by Professor Loeb.^ Those 

 figures also illustrate the thesis that the aeolotropy of the dis- 

 tinctly developing segments of the egg must be nearly the 

 same, and that component or resultant equipotential surfaces 

 are developed by the interacting molecular machinery of such 

 coherently developing or compound larvae. 



The angular divergence of duplicated tails and toes as well 

 as the axes of monstrous embryos is explained by Barfurth's 

 discovery, taken together with the principle that division of a 

 germ does not change the aeolotropy of its segments. If this 

 interpretation is the correct one, the origin of supernumerary 

 digits must be traced back to mechanical disturbances of the 

 processes of ontogeny. The rationale of the manner in which 

 divergent supernumerary toes may be produced is shown in 

 Fig. 3, representing the regenerating toes of the foot of a sala- 

 mander. 



If the toes were cut straight across at the points I, II, III, 

 nil, the toes would regener- 

 ate normally. If, however, 

 the regenerating surfaces 

 were divided into two areas 

 in each case by a line along 

 which regeneration were pre- 

 vented, two toes would arise 

 ■ from each surface. The an- 

 gular divergence of the pairs 

 of supernumerary toes thus *•' """■•'' 



produced would be measured 



by the angular inclination to one another of the two areas at 

 the end of each original toe that was thus doubly regenerated. 

 In other words, supernumerary digits are the results directly or 

 indirectly of something akin to mutilations. That such dupli- 

 cations may be produced by mutilations there can be no doubt, 



1 Biological Lectures (No. III). Delivered at Woods Holl, Mass., in 1893. 

 Ginn & Co., Boston. 



