256 HANS PRZIBRAM 



found on the right and left part of the body, this may well be 

 attempted. It may be recalled that many decapod Crustacea 

 present an unequal development of the chelae, a phenomenon 

 which I had described as 'heterochely,' and of which the pho- 

 tograph of Alpheus ruber (fig. 3) may serve as an example. All 

 crayfish in which heterochely is independent of their sex, and 

 which show no other asymmetry in their organization, are cap- 

 able of transforming the small chela into a large one, while a 

 small chela regenerates in the place of the original large chela, if 

 the removal of the large chela occurred at a sufficiently early 

 stage. This reversal of chelae was first observed in Alpheus 

 dentipes, of which a photograph is shown in fig. 4. 



The interchangeability of the chelae indicates that the capacity 

 of forming a large chela is present on both sides of the organism, 

 but the development of the new potentiality and the transforma- 

 tion does not involve a reversal of the symmetry of each chela; 

 on the contrary, while the crusher and nipper character of the 

 claws become thus reversed, both the right and the left chelae 

 retain the symmetry of the right or left side. Whereas in Alpheus 

 individuals not operated upon may have the large or crusher claw 

 either on the right or left side of the body, there exist other hetero- 

 chelous decapods in which the first differentiation of the crusher 

 claw occurs always on a definite side. 



In our common heterochelous crabs, Carcinus, Portunus and 

 Eriphia (the last is shown in fig. 5) this is always the right side, 

 and left handed individuals, as I have proved experimentally, 

 arise through the reversal of the claws occasioned by the loss of 

 the right chela. When big crabs are used, representing older 

 stages, the change from the right-handed to the left-handed con- 

 dition proceeds very slowly, and at first the chelae appear of equal 

 size, because the regeneration of the small claw instead of the 

 large crusher is fully completed while the previously small, left 

 claw has not yet transformed itself into a crusher. This secondary 

 homochely is illustrated by a photograph of a regenerating 

 Eriphia (fig. 6), which represents also a monstrosity of an 

 extra double dactylopodite borne on the right chela. This 

 monstrosity found in nature must be recognized as having been 



