192 LECTURES ON BIOLOGY 



versely, in warmth the eggs of the summer-form will duly 

 produce once more a summer-form. Analogous results were 

 produced by experiments made with other butterflies in which 

 seasonal dimorphism occurs. We have, therefore, good grounds 

 for believing that the different races of the various species of 

 butterflies which live in the Northern zones were produced by 

 climatic influences. This is in particular proved by a case 

 mentioned by Eimer. ' The common Lycseniad, Polyommatus 

 phlceas, which occurs from Lapland to Sicily, has in Lapland 

 one generation, in Germany two. But only in South Germany 

 are these two generations distinct ; in North Germany they are 

 still identical.' 



' Another Blue, Lyccena agestis, exhibits a double seasonal 

 dimorphism, for it occurs in three forms. A and B in Ger- 

 many alternate as winter and summer forms. B and C in Italy 

 occur successively as winter and summer forms. Form B, 

 therefore, occurs in both climates, but in Germany as a summer 

 form, in Italy as a winter form. The German winter form A 

 is entirely absent in Italy, whilst the Italian summer form does 

 not occur in Germany. We have here a distinct if small 

 chain of changes, obviously caused by climatic conditions.' 



As in the higher animals, so in the butterflies the sexes 

 frequently differ widely in appearance. The male ' lemon- 

 butterfly ' (Rhodocera rhamni) is distinguished by a brilliant 

 yellow colour, but the wings of the insignificant female are 

 pale yellow, almost of a whitish hue. If we keep the pupae at 

 room temperature the seasonal dimorphism disappears, and the 

 female butterflies, too, rejoice in the decorative colours of the 

 male. Standfusz has further succeeded with the magnificent 

 Parnassius apollo to give by warmth to the female the colour 

 of the male, by cold, to the male the colour of the female. When 

 we see this correlation of temperature and colour and design 

 in animals is it a wonder that doubts should arise whether so- 

 called protective coloration and colour-adaptation can be regarded 

 as a result of natural selection? Is it not rather more likely 

 that the colouring, etc., is the effect of different stimuli which 

 so far we have been unable to analyse ? 



Like heat and cold, light has a far-reaching influence upon the 

 shape and colour of the organisms. Everyone knows that the 



