No. 570] 



SPECIES-BUILDIXG 



329 



It has long been known that these two species hybridize 

 in the Mississippi Valley, where both occur. By extended 

 experiments during the past summer and previous au- 

 tumn with eurytheme stock sent to me from Arizona 

 through the kindness of Messrs. V. L. Wildermuth and 

 R. N. Wilson and with philodice from Xew I rainpshire. T 

 have found that the two species mate together readily, and 

 produce vigorous offspring. The species-hybrid males 

 were then mated with eurytheme females, and more than 

 half of the pairs (viz., four out of seven) were fertile. 

 Mated together, however, the species-hybrids showed 

 much sterility. Out of ten such matings, nine were in- 

 fertile. From - the tenth pair, nineteen adult butterflies 

 were produced. 



Orange in this cross is distinctly dominant over no 

 orange, or yellow, but the color of the heterozygote is a 

 pale orange overlying yellow, and is by no means as bril- 

 liant as the almost fiery orange of the large, summer 

 seasonal variety, the typical 11 eurytheme." In broods 

 emerging the last week in August and the first three 

 weeks of September, when intense color may be expected, 

 the heterozygote is pale orange, corresponding approxi- 

 mately to the variety known as keetvadin, whereas those 

 raised in the greenhouse and emerging early in December, 

 resemble the small orange-yellow winter type known as 

 ariadne. Keeieaydiu, according to Wright. 8 occurs at all 

 seasons in California, though probably more abundantly 

 in spring and autumn. Hence he regards this as the 

 typical variety, rather than "eurytheme." It is inter- 

 mediate, however, in size and intensity of color. 



In general, therefore, there is an incomplete dominance 

 of orange, the color of the heterozygote corresponding 

 either to that of the intermediate or to that of the winter, 

 seasonal variety of eurytheme, depending upon the time of 



