ORIGIN OF A POLYDACTYLOUS RACE OF GUINEA-PIGS. 29 



POSTSCRIPT. 



A critical examination of the results obtained by Bateson, Punnett and 

 Hurst (see Bateson, Saunders, Punnett and Hurst, :o5) in poultry indicates 

 that there too the inheritance of extra-toe is not strictly Mendelian, but cor- 

 responds with what I have found to be the condition in the most [>otciit poly- 

 dactylous sires. In poultry the extra-toe has been for a long time an estab- 

 lished character of certain breeds. During all that time selection has un- 

 doubtedly been exercised in its favor, so that it is not surprising to find the 

 character more strongly dominant than in my four-toed race of guinea-pigs. 

 Nevertheless both Bateson and Hurst record cases in which polydactylous 

 chicks are produced by normal parents of polydactylous ancestry. 



Similar observations have repeatedly been made concerning the inher- 

 itance of polydactylism in man. See Ballowitz ( 104) and Davenport ( :o4). 

 Polydactylism usually makes its (recorded) appearance in some note-worthy 

 form, is transmitted more or less strongly through two to five generations 

 and then disappears, doubtless so weakened by repeated out-crosses that its 

 manifestations, if any occur, are no longer observed. 



Apparently it is only when selection is exercised for the polydactyl 

 character and like individuals are mated to each other that a polydactylous 

 race can be established. In its origin, polydactylism is a discontinuous varia- 

 tion or mutation, but without the aid of selection it would probably never 

 become a racial character. Is not the same thing true of a great many of 

 the characters which serve to distinguish the various races of domesticated 

 animals and plants? 



11. BIBLIOGRAPHY. 

 Ballowitz, E. 



:04. Ueber hyperdactyle Familien und die Vererbung der Vielfingerigkeit des 

 Menschen. Archiv. f. Rassen-und-Gesellschafts-BioI. Bd. i, pp. 347- 

 365, II Fig. 

 Bateson, W., Saunders, E. R., Punnett, R. C, and Hurst, C. C. 



:0S. Experimental Studies in the Physiology of Heredity. Report II. to the 

 Evolution Committee of the Royal Society. 154 pp. 

 Castle, W. E. 



:0S. The Mutation Theory of Organic Evolution, from the Standpoint of Animal 

 Breeding. Science, n. s., vol. 21, no. 536, pp. 521-525. 

 Davenport, C. B. 



:04 Wonder horses and Mendelism. Science, n. s., vol. 19, no. 473, pp. 151-153. 



