76 PROBLEMS OF GENETICS 



crushing claw. Accepting this interpretation, we reach the 

 remarkable conclusion that the bud of new growth consisted of 

 halves differentiated into cutter and crusher as the normal claws 

 are, and that the extra crusher is geometrically a left but physi- 

 ologically a right. Though shaped as a left in respect of the 

 direction in which it points, the extra crusher is really an op- 

 tically reversed right, while the dactylopodite R, which is 

 placed pointing like a right, is really a reversed left (Fig. 12). 



If these indications are reliable 9 and are established by further 

 observation we shall be led to the conclusion that the bud which 



FIG. 12. Right claw of lobster bearing a pair of extra dactylopodites (after 

 van Beneden). The fine toothing on R suggests that this is part of a cutting 

 claw, though the limb bearing it is a crusher. 



becomes an extra pair of limbs does not merely contain the parts 

 proper to the side on which it grows, but is comparable with 

 the original zygotic cell, and consists not simply of two halves, 

 but of two halves differentiated as a right and a left like the two 

 halves of the normal body. 



Phenomena of this kind, evoked by mutilation or injury, 

 together with the cognate observations on regeneration throw 



9 Dr. Przibram, I should mention, concludes that on the whole the facts are 

 against this interpretation, but as more evidence is certainly required, I call at- 

 tention to the possibility. 



