From the Department of Comparative Anatomy, Harvard Medical School, Boston, Mass. 



THE EXPERIMENTAL CONTROL OF ASYMMETRY 

 AT DIFFERENT STAGES IN THE DEVELOPMENT 

 OF THE LOBSTER. 



VICTOR E. EMMEL 

 INTRODUCTION 



The asymmetry of decapod Crustacea has recently been studied 

 by Przibram ('or, '02, '05, '07), Morgan ('04), Zeleny ('05) and 

 Wilson ('05). This asymmetry is manifest in the first pair of 

 claws or chelae — one of which is larger and frequently structurally 

 different from the other. It has been found in some cases that 

 if the large chela is removed, a small one may regenerate in its 

 place. At the same time, the original small chela on the opposite 

 side of the body may grow into a large one. This transposition 

 of chelae is known as "reversal of asymmetry." A complete 

 reversal of asymmetry follows the amputation of the large chela 

 in the adult of Alpheus as shown by Przibram and Wilson. On 

 the other hand, such a reversal is not obtained in similar experi- 

 ments with the adults of the hermit crab and lobster as found by 

 Morgan and Przibram. This I have confirmed in regard to the 

 lobster by experiments with over 200 adults, in none of which was 

 there obtained a transposition of the chelae. 



The previous studies have dealt only with adult animals. In 

 view of this fact it seemed desirable to investigate the estabHsh- 

 ment of asymmetry at various stages in the growth of the lobster — 

 one of the forms in which reversal does not occur in the adult. 

 This has been done with the results about to be described. 



The work was carried on at the Experiment Station of the Rhode 

 Island Commission of Inland Fisheries, and I desire to express my 

 indebtedness to Dr. A. D. Mead for generously permitting me to 



The Journal of Experimental Zoology, vol. v, no. 4 



