1898.] appbjSTkages in the arthropoda. 953 



(6) The joints of the reproduced portion have relative dimensions 

 which are different from those of the normal joints and 

 render any scheme of identity therewith of doubtful value. 



(c) If the terminal joint or joints of the normal appendage are 

 differentiated from those more proximal, then the terminal 

 joint or joints of the reproduction are similarly differ- 

 entiated in spite of their want of agreem.mt in numerical 

 se(;[uence with the joints of the normal. 



(vii.) Tiie peculiar distinguishing features of reproductions 

 unlike the normal are perpetuated through all subsequent ecdyses, 

 the Jiormal structure not being reassumed at any time. 



(viii.) The reproduced portion of an appendage, whether it is of 

 the type exactly resembling the normal or of the type which 

 differs therefrom as above described, possesses the power of 

 growing with special rapidity, so that, always smaller than 

 its congenital fellow on its first appearance, it sooner or later 

 attains a symmetrical size, provided that this is not prevented by 

 the cessation of general growth. 



(ix.) The structural characters of reproductions which are 

 unlike the normal often possess a high degree of organic stability, 

 and in some cases at least a degree which is quite comparable with 

 that possessed by the characters of the congenital structure the 

 reproduction takes the place of. To account for this high stability 

 in a reproduced structure by the operation of selection seems 

 impossible. 



(x.) In the instance of such a reproduction afforded by the 

 4-jointed tarsus of Blattidse, so establislied is the nature of the 

 reproduced appendage, that when the animal possessing it attains 

 maturity, the relative proportions of its joints undergo the same 

 kind of change as that which is normal in the congenital form of 

 tarsus. It is thus obvious that a reproduction of this kind may 

 not only possess a structural stability comparable v/ith tliat of the 

 normal, but also be dominated by a trophic control so specialized 

 that the changes proper to the several stadia are brought about in 

 the reproduced just as they are in the congenital appendage, being 

 unimpeded by the profound structural differences between the 

 two. 



I must express my thanks to Mr. Adam Sedgwick for placing at 

 my disposal the facilities of the Zoological Laboratory at Cambridge 

 for this work, and to Mr. W. Bateson, not only for the suggestion 

 which incepted the inquiry, but for kind advice and criticism 

 during its progress. 



References to Literature. 



1. Bate, C. Spence. — "Eeport of the Committee appointed to ex- 



plore the Marine Fauna and Plora of the South Coast of Devon 

 and Cornwall." No. 2. Brit. Assoc. Eep. 1868, p. 283. 



2. Bateson, W. — ' Materials for the Study of Variation,' 1891, 



pp. 63 & -115. 

 Proo. Zool. Soc— 1898, No. LXIII. 63 



