CLIMATIC VARIETIES 175 



incline to answer this question by reference to segregation, and 

 perhaps by an appeal to selective mating. The suggestion that 

 segregation does take place is certainly true to some extent. 

 There are, however, difficulties in the way, and the whole subject 

 is one of great complexity. My own experiments were made in 

 pre-Mendelian times and were not arranged with the simplicity 

 which we now know to be essential. The results are neither 

 extensive enough nor clear enough to settle the many collateral 

 questions which have to be considered, and the work ought to 

 be done again. Nevertheless, some notes of the observations 

 may have a suggestive value. 



When I began, I did not sufficiently appreciate that the 

 "napi" group, omitting the North American forms, and the 

 Asiatic representatives, has at least three chief types in western 

 Europe. The differences we have to deal with are manifested 

 by the females only, so in this account particulars as to the males 

 are omitted for the most part. These are (1) our own British 

 napi; (2) the form found in the south, from the Loire downwards, 

 and in the Italian Alps, which I think may be spoken of as 

 meridionalis; (3) bryoniae, which is a form clearly recognizable 

 in the female only, and is found only in the arctic regions and 

 in the Alps above 2,500 feet. The first two have several broods, 

 two, three, or more, according to opportunity, and the first 

 brood is different from the later ones. In napi the markings on 

 the upper surface are a dark grey but in meridionalis they are a 

 pale silvery grey and much less extensive. In the later broods 

 of napi there is much less general irroration of the veins, and the 

 spots stand out as more defined and blacker. These differences 

 vary greatly in degree of emphasis. In meridionalis the later 

 broods are entirely different from the first. Instead of having 

 silvery markings they have the ground colour quite white, with 

 the spots large and a full black. On the under side of the hind 

 wings the usual green veins are almost absent, and I have seen 

 individuals which could scarcely be distinguished from rapae. 

 To these later broods the term napaeae is sometimes applied, 

 but I here use meridionalis for the southern race in general as 

 applicable to all broods. 



