482 Victor E. Emmel 



Przibram ('07), in his recent extensive work on ''Die Scherenum- 

 kehr bei decapoden Crustaceen," found experimentally that a 

 reversal of chelae could be obtained in six genera and eleven species 

 of Crustacea, including forms in both the Macrura and Brachyura. 

 He then inquires whether this capacity for reversal of asymmetry 

 is a constant characteristic for a given species. Here he finds 

 that the statement that a reversal of asymmetry always follows 

 the amputation of the crusher ("^ — schere") in a crustacean 

 requires modification. For it appears that the readiness with 

 which reversal occurs varies inversely with the size of the animal. 

 Specimens of Athanas, Alpheus, Typton, Callianassa, Carcinus 

 and Portunus, which are under 10 mm. in carapace length, 

 showed a quick and complete reversal of asymmetry. But, on the 

 other hand, the larger specimens showed a decrease in the tendency 

 toward transposition of the chelae, so that when the large chela is 

 removed the chela on the opposite side retains its original form. 



It appears therefore that the relations found in the control of 

 asymmetry at difi'erent stages of development in the lobster, are 

 also true for other Crustacea with asymmetrical chelae. For both 

 in the lobster and in the forms described by Przibram, the various 

 stages in their development form a series beginning with a com- 

 plete control of asymmetry and ending with the disappearance of 

 such control. In other words, the possibility for experimental 

 control and reversal of asymmetry seems to be correlated in some 

 way with the degree of differentiation or development, so that the 

 greater the degree of development the more stable is the asymme- 

 try of the organism. 



SUMMARY 



1 In the first four stages of the lobster's development, a crusher 

 may be produced on either the right or the left side of the body by 

 the autotomous amputation of the chela on the opposite side — the 

 regenerated chela becoming a nipper. 



2 During the fifth stage, although the chelae are apparently 

 still symmetrical, the possibility for such experimental control 

 disappears. 



