4 PHYSIOLOGICAL GENETICS 



process or processes; and in both cases, the quantity and quality 

 of the possible change are limited by the degree of freedom left 

 to the individual developmental processes without destroying 

 their integration into :i more or less normal whole. 



These considerations show that it is <>i primary importance 

 for an understanding of the action of the gene to compare tho 

 effects of the mutated gene upon development with effects 

 produced by external agencies upon the development of the Wild 

 type. 



1. THE PHENOCOPIES 



A. Description 



In his classic researches upon the wing pattern of butterflies, 

 Standfuss (1896) showed that it is possible to change this pattern 

 by the action of extreme 1 temperature in the pupal stage so that 

 the experimentally produced pattern cannot be distinguished 

 from the pattern of known races of the same species; e.g., heat 

 treatment of the Swiss Papilio podalirius could produce a form 

 looking like the variety P. zanclaeus found in Sicily. Central 

 European Papilio machaon pupae treated with heat gave rise 

 to butterflies resembling the Syrian race P. sphyrus or the 

 Turkestan race P. centralis. Central European Vanessa urticae 

 pupae treated with low temperature produced types like the V. 

 polaris from Lapland ; and the same treated with heat gave forms 

 indistinguishable from the race V. ichnusa of Sardinia (Fig. 1). 

 In this case, the geographic races that were copied in the experi- 

 ment were known to be constant and therefore presumably 

 genetically different from the main form, though this genetic 

 difference \vas not established. 1 The facts were used mostly 

 for phylogenetic and Lamarckian speculations, and only in 

 1917d, 19206, and 1927c did Goldschmidt point out their impor- 

 tance for the understanding of the action of the gene. Recently 

 Goldschmidt (1935a) proposed the term phenocopy for such forms, 

 produced experimentally from the Wild-type form, the phenotype 

 of which copies or duplicates the appearance of a mutant (or 

 combination of mutants) of the same form. We shall use this 

 term henceforth. 



1 In other experiments, heat treatment of female pupae produced the male 

 type of wing pattern. Here, of course, as we know now, the normal differ- 

 ence is controlled by genes. 



