172 PROBLEMS OF GENETICS 



from Gallipoli (E. M. M., 1 88 1, p. 95). Staudinger does not 

 distinguish the intermediates from the northern, but he gives 

 "egerides" for Armenia and Fergana (Central Asia). As against 

 the mere proximity of a great mountain chain being the influence 

 which keeps the Riviera population intermediate may be 

 mentioned the fact that the northern foothills of the Pyrenees 

 have the pure southern type, and the climate of Cambo must 

 surely be far cooler than that of Nice. The exact locality of 

 the Greek specimens is not given, but there can be no part of 

 Greece which is not much hotter in summer than Brittany, or 

 Calvados, which have the intermediate, not the English type. 

 In face of these facts it can scarcely be maintained that 

 average temperature is the efficient cause of the particular tone 

 of colour which the butterfly shows in a given region. Never- 

 theless it is clear that climate counts for much in determining 

 the distribution. It is noticeable that though the pale egerides 

 can be established in a warm climate we never find egeria in cold 

 climates, and even the intermediate is not found in places that 

 have a hard winter. I suspect that the distribution of the 

 broods through the year and the condition of the animal at the 

 onset of hard frost are features which really determine whether 

 a strain can live in a particular place or not. Though the truth 

 of the suggestion cannot be tested by experiments in captivity, 

 which at once introduce disturbances, I incline to the idea that 

 egeria has not got the right periodicity for northern climates. 

 If it could arrange its life so that the population consisted either 

 of young larvae, or perhaps of thoroughly formed pupae 11 at 

 the onset of winter, it might, for any obvious reason to the 

 contrary, be able to live in England. It is irregularly "poly- 

 voltine," as the silk-worm breeders say, and as soon as a little 

 warmth encourages it, a new generation starts into being, which 

 if the frost comes at an untimely moment, is immediately 



11 My experience agrees with that of Mr. H. Williams (Ent. Rec, VIII, 1896, 

 p. 181) that pupae, well-formed, can stand considerable frost; but I used to find 

 that half-grown larvae usually died if unprotected, and I believe that larvae which 

 attempted to pupate in warm autumn weather and then got caught by frosts, 

 always died. Small larvae which can creep into shelter at the bottom of the plants 

 survived, and I expect that in the north the winter is usually passed in that state 

 (see also Merrifield, F., Ent. Rec, VIII, 1896, p. 168, and Carpenter, J. H., ibid.). 



