286 BULLETIN OF THE BUREAU OF FISHERIES. 



always so. Distortions arise which may have been caused by a pinch and arrest of 

 growth while the claw was soft or by injury to the stump. In the latter case the 

 member might be only partially restored, and unequal growth would account for 

 the defect. 



A small budUke swelling is sometimes seen near the apex of either division of the 

 claw, and it formerly seemed to me improbable that this could be due to a simple 

 injury since such appearances are rare, while injuries to the big claws must be excessively 

 common. I further assumed that, given such an outgrowth, a progressive series of 

 changes might take place with successive molts, the swollen part becoming bifid and 

 eventually completely divided. To continue the account upon this basis: With the 

 growth of the animal, the superadded part, whether it be upon dactyl or propodus, 

 seems to be shifted at each molt farther and farther back upon the claw, and meantime, 

 in most cases, to undergo fission in a vertical or somewhat oblique plane. This fission 

 apparently proceeds until one or both of the supernumerary dactyls are entirely 

 separated. The opposing edges of these become gradually toothed, so that each is 

 almost an exact copy of the original. According to the principles laid down by Bateson, ' 

 the part which is nearer the original joint corresponds with the appendages on the 

 opposite side, that which is farthest away with those on the same side of the body. 

 Many cases occur, however, which do not conform to this and apparently to no other 

 rule (see J49, p. 144-148). 



Since the appearance of my earlier work referred to above, the excellent researches 

 of Przibram {220-223) ^^d Emmel have added greatly to our knowledge of this 

 subject. The former has shown that in all probabiUty monstrous growths of every 

 kind result from a regenerative process following upon injury. However, such growths 

 are comparatively rare and follow only upon injury of a certain kind, or upon an 

 injury inflicted at a certain time with respect to the molting period, or under certain 

 conditions of the animal which are not fully understood. 



Przibram found that when an injured leg was retained duplication of the part 

 might arise through a division of the regeneration rudiment, as in vertebrates, and it 

 was further shown by Miss Reed that when a leg of the hermit crab is thrown off, if the 

 base is split lengthwise so as to divide the nerve, there often appear two new legs, each 

 connected with one end of the nerve. It would thus appear that duplication of a limb 

 is subject to the will of the experimenter, and that duplicated parts may often arise in 

 nature through an accidental injury to the nerve rudiment. Further, in 1905 Zeleny 

 {290) obtained by experimental means the regeneration of a double chela in the fiddler 

 crab. Two cases where duphcation of parts of the big claw followed directly upon 

 injury to the claw itself or to a regeneration bud have been recorded by Przibram {223) ; 

 the first concerned a specimen of Portunus hastatus, which suffered in an aquarium the 

 loss of both points of its big right claw in an irregular manner, and regenerated within 

 three months; after molting, the dactyl became doubled, while the propodus was 

 unchanged. The second case arose through an artificial division of a normal regenera- 

 tion bud of the last walking leg of a Carcinus maenas. The operation was performed 

 with fine scissors on May 14, 1901, and after the molt, which occurred on June 2, the 

 protopodite showed two separated dactylopodite buds. Since this animal died on 



