178 PROBLEMS OF GENETICS 



To obtain really exact knowledge of the number of factors 

 and their properties it would be necessary to repeat the work. 

 After the beginning, I made a mistake in using British napi 

 instead of meridionalis and the results were much confused 

 thereby. The contrast between meridionalis and the various 

 dark forms is much greater and classification of the types would 

 have been therefore easier. The British form is presumably 

 meridionalis plus the factor for the basal pigmentation. The 

 problem is greatly complicated by the differentiation of the 

 seasonal forms. The first point to be determined is whether 

 bryoniae is capable of producing a second brood when it is thor- 

 oughly pure-bred, and whether such a second brood is, as I 

 suspect, normally intermediate in character. 



In the Alps generally there is no definitely intermediate 

 population; nor I believe, is any such population met with in 

 the north where the arctic bryoniae meets napi, but as to this 

 I have no precise information. One curious fact, however, must 

 be mentioned, namely that there is a population that can prob- 

 ably be so described with fairness established at Modling near 

 Vienna. This is not in any sense an Alpine locality, and does 

 not, as I am told, differ in any obvious way from the other sub- 

 urbs of Vienna. Dr. H. Przibram was so good as to send me a 

 set taken at this place, representing a second brood, and they 

 were decidedly heterogeneous, ranging from an intermediate 

 form such as bryoniae fertilised by napi usually produces, to a 

 light yellowish second-brood type with little dark pigment. 

 There are also two actual bryoniae. Whether true napi also 

 occur there I do not know, but I have no doubt they do. It 

 would be well worth while to investigate the Modling population 

 statistically, and to breed from the intermediates which might 

 not impossibly prove to be heterozygotes. There are also records 

 of such intermediates being occasionally found in some parts of 

 Ireland, in the north of Scotland, and in south Wales, 19 but I do 

 not know of any regular colony of these forms. We can scarcely 

 avoid the inference that one or more of the factors which make 

 up bryoniae may be carried by these intermediates. It is not 



19 See figures in Barrett, G. C., Lepidoptera of Brit. Islands, I, pt. 3, p. 25. 



