REVERSAL OF ASYMMETRY IN ALPHEUS. 2O3 



the dactylus of the male small chela, which is entirely absent in 

 the more modified forms (c. g. t in Fig. 2, B, E}. A comparison 

 of the figures will show that in every respect the specimen is 

 intermediate between the unmodified male small chela (Fig. 2, 

 A) and the more modified form (Fig. 2, B). In specimens of 

 9 days the setose ridge of the dactylus has wholly disappeared 

 (Fig. 3, B] and, except for its somewhat more slender form, is 

 as characteristic as in those of two weeks or more (Fig. 2, E). 



SECOND SERIES. 



In a second series the same operations were performed, but in 

 addition the nerve supplying one or both stumps was cut below 

 the base of the appendage. In one set (C) the large chela was 

 removed and the nerve of the remaining small chela on the 

 opposite side was cut ; in a second set both chelae were removed 

 and the nerves of both stumps cut. This operation, easily per- 

 formed by means of a slender sharp-pointed scalpel, results in 

 the first case in a complete paralysis of the remaining appendage. 

 If after a few days control of the appendage was regained, as 

 often happened before the ensuing moult, the operation was as a 

 rule repeated. The mortality in operations of this type is large, 

 and many of the specimens sooner or later cast the remaining 

 appendage ; hence only eight successful cases were obtained, and 

 of these only two are beyond question. 



C. Of eleven cases in which the large chela was removed and 

 the nerve of the remaining small chela was cut, nine regenerated 

 without reversal, one with reversal, and one with both chelae of 

 the large type. 



D. Of three cases in which both cheloe were removed and the 

 nerves of both stumps cut, all regenerated .without reversal. 

 These cases differed from those recorded under B only in show- 

 ing a slight retardation in regeneration. 



Of the first nine cases recorded under C seven had thrown off the 

 small claw at a varying period before the moult and hence are 

 without value ; for such specimens have lost both chelae. Ex- 

 periments to test this point show in fact that if the large chela be 

 removed and the smaller one be subsequently removed, after a 

 period sufficiently long to admit of complete reversal under 



