DOUBLE CHELA IN THE FIDDLER CRAB. 



153 



completely separates the two dactyls and forms a very distinct 

 groove in the propodite. 



One of the resultant pinchers (DI] the one more directly in 

 the line of the axis of the chela is stouter than the other. In 

 the stouter chela the dactyl and index are approximately of equal 

 length. In the smaller chela (D'f'J the dactyl is very notice- 

 ably longer than the index. Except for these slight differences 

 and the more slender character of the smaller chela it is a per- 

 fect mirror image of the other. As the split is deeper on the 

 index than on the dactyl side, the dactylopodites are nearer 

 together than are the indices. The planes of the two chelae 



D 



I 



FIG. I. Double chela of Gt-Iasinnts pitgUator (X I 2 )- Left figure : viewed from 

 pollex border. Right figure : viewed from index border. 



therefore converge slightly on the dactyl side and diverge on the 

 index side. In life both parts of the double chela functioned as 

 pinchers. 



DISCUSSION. 



The double chela which has been described evidently comes 

 under the group of true double appendages, a group the exist- 

 ence of which Bateson ! was loath to admit since he considered 

 the possibility that the supernumerary appendage in such cases 

 is in reality itself double, as is true in a great number of the 

 abnormal limbs so far described. 



1 Bateson, " Materials for the Study of Variation," 1894. 



