AN ABERRANT LIMB IN A CRAY-FISH. 



E. A. ANDREWS. 



A striking aberration in the form of a third, left-walking leg 

 of a female Cambarus Bartoni found in class dissection in Febru- 

 ary, 1892, seems of enough interest to warrant its being put on 

 record. 



A view of the anterior face of the limb (Fig. i) shows a mark- 

 edly forceps-like structure in addition to the usual forceps at the 

 end of the limb, so that there are four instead of the usual two 

 terminal points. 



The added structure is, however, not a true forceps with one 

 movable finger, but a movable piece with two immobile prongs 



FIG. I. Camera sketch of anterior face of left third leg of C. Bartoni. Genita 



opening indicated in black. 



that otherwise resemble the index and pollex of a forceps. This 

 is evident in the enlarged view, Fig. 2. 



The real forceps in this limb is nearly normal, but on compar- 

 ing it with an anterior view of the third walking leg of a normal 

 C. Bartoni (Fig. 3), of about the same size, we may note some 

 differences. Thus, in place of the straight-lined articulation of 

 dactyl and propodite, we find the propodite presenting a hollowed, 

 socket-like face where the dactyl articulates. Again, while the 

 dactyl and the index are both normal in form, the dactyl is not 

 a straight continuation of the propodite, but bends down at a 

 noticeable angle, thus increasing the wide divergence of the 

 double set of tips of this limb. 



The propodite departs from the usual form in being wider dis- 

 tally where it bears, as it were, a large protuberance that is 



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