The Development of Asymmetry in the Fiddler Crab

Abstract

THE experiments of Przibram ('01, '07, '17) and of others have shown in certain species of decapod crustaceans, in which a larger and a smaller "claw" are normally present, that after the removal of the large claw the smaller claw develops into a large claw. In other species, however, including the fiddler crab (Gelasimus), this renewal does not take place after the removal of the large claw. A new large claw regenerates on the stump of the old one. It was known (Hyman, 1920) that in the earliest stages of the fiddler following the Zoea the two claws (first pair of legs) are equal in size and in shape and are like those of the female or like the small claw of the male. I tried to find out whether, if one claw is removed from young male crabs in these undifferentiated stages, the remaining claw will develop into a large claw. It was necessary first to find at what stage the difference in size of the two claws first appears in the young crabs. Here a new fact of some interest came to light. Collections of young crabs were made at North Falmouth, Massachusetts, on July 10, August 3, September 2 and 15, 1922. Those collected on July 10 were crabs of the preceding summer and will be described later. A iew generation came to land in August and September and those of September 2 and 15 give the results shown in the following table. The crabs fall into three groups: (1) those with unequal claws ("male" and "female" claws, or else juvenile, Fig. 1, c; and Fig. 2, b; and Fig. 3,