BRISTLE INHERITANCE IN DROSOPHILA 457 



complete the conception that is held by most adherents of the view 

 that multiple factors or modifying genes are responsible for the results 

 of selection (p. 51). 



Among the authors who do not accept the substance of the 

 multiple-factor theory may be mentioned Goldschmidt and Sum- 

 ner. Goldschmidt ('18) gives a brief outline of experiments 

 with gyspy-moths. His results are said to agree closely with 

 those of Castle. Different races are characterized by different 

 amounts of pigment in the larval stages; crosses between any of 

 these races always give simple 3 : 1 ratios. In certain races the 

 degree of pigmentation shifts with the successive stages of larval 

 development; a time factor introduced that is inherited indepen- 

 dently of the color factor and determines the degree of pigmenta- 

 tion that is finally attained. The interpretation is based on the 

 hypothesis than an extensive series of multiple allelomorphs is 

 involved in distinguishing the different races. These really are 

 different quantities of a substance that determines the velocity 

 of the reaction of pigment formation. Given a constant develop- 

 mental factor and the quantity of this substance will always 

 determine the degree of pigmentation reached. In support of 

 the idea that even within the same race the amount of this sub- 

 stance may vary and so yield to selection, the results of selecting 

 in the Fi of a cross are cited. Although the F2 gave the 3 : 1 

 ratio as always, the grades of the offspring from different Fi 

 grades were correspondingly different. Hence there were vari-' 

 ations in the substance in the parent races. The full report of 

 Goldschmidt's experiments will present much interesting and 

 valuable data, but, if the phenomena shown by his moths so 

 closely resemble those shown by the hooded rats, one wonders if 

 the same interpretation will not be required by both experiments. 

 Either the Goldschmidt theories will have to be made to fit the 

 mass of data that leans in the opposite direction, or else the full 

 data will be found to accord with the hypothesis that the majority 

 of experiments seem to demand. 



From the behavior of different geographical races of Peromiscus 

 when the environments were interchanged and when raised in 

 cages in the same environment, and when crossed, Sumner ('18) 



