480 Victor E. Emmel 



neither one nor both chelae produced a reversal of the original 

 asymmetry. 



DISCUSSION 



Until recently the phenomenon of reversal of asymmetry or 

 compensatory regulation, which Przibram and Zeleny found in 

 Alpheus, was not supposed to occur in such forms as the lobster 

 or hermit crab. It appeared that these species were characterized 

 by a "direct regeneration" of the original asymmetry. But the 

 discovery that under certain conditions the adult lobster might 

 regenerate a crusher from the stump of the amputated nipper 

 chela (Emmel '06^) demonstrated that in the lobster, at least, both 

 sides of the body might still retain the potentiality for the more 

 highly differentiated type of crusher claw. The present results 

 which show that asymmetrical differentiation can be controlled at 

 early stages of development in the lobster, suggest that similar 

 relations in the development and stability of asymmetry may be 

 found in other Crustacea.^ 



Various theories have been advanced concerning the factors 

 which determine right or left asymmetry, and which may be dis- 

 cussed on the basis of the preceding experiments. 



Herrick ('05) studied the shrimp Alpheus, and concluded that 

 asymmetry of the chelae in Alpheus and also in the lobster "is 

 probably one of direct inheritance, all members of a brood being 

 either right or left handed. That is to say, the normal position of 

 the toothed or crushing claw is not haphazard, but is predeter- 

 mined in the egg" (p. 225). 



Conklin ('03, '05), without discussing inheritance, shows how 

 inverse symmetry may be determined in the egg. He found rea- 

 son for believing that the cause of inverse symmetry, which occurs 

 regularly among some species and occasionally among all, man 

 included, is to be found in the inverse organization of the egg, and 



^ It is interesting to find this suggestion already anticipated by Przibram. In his important mono- 

 graph published in the Archiv. f. Entw.-Mech., Bd. 25, 1907, p. 310 (received while the present 

 paper was being written), he discusses the question," Is the possibility of the reversal of chelas present in 

 those forms which have hitherto shown no reversal ?" He concludes that in some of these (Callianassa 

 and Carcinus) the asymmetrical relations may be altered. 



