MUSEUM OF COMPARATIVE ZOOLOGY. 265 



digits b, c, are simply processes developed from the ultimate segment of 

 the leg without the least mobility. We have here a structure which is 

 neither morphologically nor functionally a claw, but only a counterfeit of 

 one. What force produces the perfect development of teeth on the op- 

 posed edges of these immovable digits, where they cannot be of the 

 slightest service ] It is to be observed that these spurious chelse are 

 always found on the dactylus of claws which have lost their function 

 through the displacement of the dactylus. In such cases there seems 

 to be a futile effort to form a new claw in the way indicated. When 

 one sees how perfectly the dactylus a (e. g. in Plate I. fig. 5) is repeated 

 in the process b, and the index in the process c, even to the details of 

 dentition and setse, he is at once tempted to call upon Darwin's hypothe- 

 sis of pangenesis f to explain the resemblances. It will be observed 

 (see Plate I. figs. 13, 16, Plate II. fig. 6) that a movable dactylus may 

 be duplicated on the propodal segment, but in no case is an articulated 

 segment developed from the dactylus. 



It would be extremely interesting to know whether these monstrous 

 developments are perpetuated throughout the life of the individual, or 

 whether they are got rid of by exuviation. The latter seems hardly 

 probable. Huxleyj says the deformities persist, but whether this state- 

 ment be based on observation or not, I do not know. 



As the specimens which have come under my observation are dry, and 

 the soft parts removed, I can record nothing concerning the arrange- 

 ment of the muscles, nerves, and arteries in those deformed claws. 

 What modifications of the soft parts are brought about by the deformi- 

 ties would be a most interesting subject of study for any one who may 

 come into possession of such specimens in a fresh or alcoholic state. 



Almost all the malformations of the hard parts of Crustacea which 

 have been described are confined to the big claws. These claws, being 

 the chief weapons of offence and defence, are much more liable to receive 

 wounds than any other part of the body, and, as before pointed out, de- 

 formities such as are described in this paper are undoubtedly in most 

 cases the result of injuries. Rb'sel (No. 4) speaks of deformities of the 

 rostrum of crayfishes; Herklots (Nos. 11, 15) describes and figures a 

 triple dactylus of the second pair of legs in Lithodes arctica ; A. Milne 



* In such specimens as that figured on Plate I. fig. 8, where the chela has its func- 

 tional power, the spurious claw is formed in a different way, a being the original 

 dactylus. See p. 258. 



t The Variation of Animals and Plants under Domestication, Vol. II. Ch. XXVII. 



| The Crayfish. An Introduction to the Study of Zoology, p. 39, 1880. 



