THE REGENERATION OF A DOUBLE CHELA IN 

 THE FIDDLER CRAB (GELASIMUS PUGI- 

 LATOR) IN PLACE OF. A NOR- 

 MAL SINGLE ONE. 1 



CHARLES ZELENY. 



The double chela described in the present paper was regen- 

 erated from the distal end of the stump of the smaller chela of a 

 male fiddler crab (Gelasiinus pugilator) after autotomy of that 

 appendage at the breaking joint. The case seems of interest not 

 only because it is a regeneration product but also because it 

 belongs to the rare class of truly double appendages. 



The crab which developed the double chela originally possessed 

 a normal small chela on the right side and a normal large chela 

 on the left and was operated on at Cold Spring Harbor on July 

 2, I9O2. 2 The nerves of the two chelae were injured by a needle, 

 the injury in each case resulting in immediate autotomy of the 

 appendage at the breaking joint. The crab was isolated and fed 

 on ]\Iytihts (horse-mussel). It moulted on August 4, 33 days 

 after the operation. On both sides the regenerated chelae were 

 of considerable size and the right or smaller one was seen to be 

 double. The crab was kept under observation for 17 days after 

 the moult, or 50 days after the operation. Two views of the 

 chela are given in the accompanying figure which shows the 

 terminal four podomeres. The first, 3 second and third podo- 

 meres are of the typical single form. The fourth podomere, how- 

 ever, is divided terminally so that there are two entirely separate 

 indices (/, /'). The split extends well down into the body of 

 the propodite on this side. In connection with each index there 

 is a dactylopodite (D, /)'). The split on the dactyl side of the 

 propodite, though not as deep as on the index side, nevertheless 



1 " Contributions from the Zoological Laboratory of Indiana L^niversity," No. 67. 



2 The operation was performed as part of a series of experiments on compen- 

 satory regulation which are described in a paper now in press under the title of 

 "Compensatory Regulation," Journal of Experimental Zoology, Vol. II., No. I. 



3 Not shown in the figure. 



I 5 2 



