AN ABERRANT LIMB IN A CRAY-FISH. 79 



i 



somewhat anterior to the free tip of the plate. The terminal 

 plates are smaller than the others and have a smaller number 

 of teeth. This number may be as high as twelve toward the 

 middle of the series. In all these respects the plates of the mon- 

 strous growth agree with those of the real claw. No difference 

 was found between single plates of the dactyl and the index, nor 

 between plates of the two prongs nor between plates of the nor- 

 mal and abnormal growths. 



The pronged structure, however, differs from the natural claw 

 both in number of plates and in their arrangement at the angle. 

 While the normal claw has 61 and 67 plates the pronged struc- 



FIG. 4. Camera sketch of posterior view of serrated plates from the abnormal pronged 



structure. 2-D. 



ture has 53 on the prong with a broken tip and 54 on the other. 

 At the angle (Fig. 2) the plates have the arrangement shown in 

 Fig. 5 : the terminal plates are crowded together and the two 

 series interfere at the angle. Plate 52 of the imperfect prong 

 steps out of rank and stands partly in between plates 53 and 54 

 of the series on the perfect prong, which is indicated by the letter 

 T on the fifty-second plate. The angle thus has plates of both 

 series carried into it till they fuse into one curved line. More- 

 over, these plates at the angle are not the same as the terminal 

 plates of the normal claw, nor do they agree in number of teeth 

 with plates at that distance from the tip of the normal claw. 

 They are evidently special terminal plates in their own series but 

 not directly comparable with the normal terminal plates. The 

 prongs are shorter than the index and the dactyl and have not 

 room for a full number of plates. Where they have a free edge 



