100 THE ENTOMOLOGIST. 



in India, we shall generally find that the Indian insect is the 

 smaller and duller coloured of the two. 



It is therefore evident that we can dismiss the idea that the 

 colours of butterflies are directly due to the abundance or absence 

 of sunshine. Everything, on the contrary, seems to point to 

 their being the outcome of the organic environment. Other 

 writers (like Mr. Tutt), more in harmony with the natural 

 selection school, maintain that colours with a melanic or melano- 

 chroic tendency are useful to their possessors by enabling them 

 to resemble their surroundings, especially when they reside at 

 high altitudes among the mountains, and thus enable them, 

 when at rest, to escape detection by their enemies. When this 

 is the case at the lower elevations I can quite agree with them 

 that the value of these sombre hues is considerable under certain 

 circumstances, but when it exists in the higher zones, where 

 insectivorous birds, mammals, and reptiles are generally so 

 scarce, its purpose is not so easy to comprehend. 



Another hypothesis, with especial reference to the genus 

 Erehia, has been launched forth by Lord Walsingham, to the 

 effect that their dark colours, by rapidly absorbing the solar 

 rays, give their possessors greater vitality when on the wing 

 than would otherwise be the case. This character, he supposes, 

 would be especially beneficial to the males in searching for the 

 females ; in other words, it is of selective value. Now it is well 

 known that rich colours in nature are generally correlative with 

 considerable vitality, and it is thus exceedingly probable that the 

 darker colouring of the males is beneficial to their possessors in 

 the manner indicated ; at the same time I do not consider that 

 it constitutes the origin of the particular pigmental colouring of 

 the genus, the primary purpose of which will have to be sought 

 for elsewhere. In support of my contention may be brought 

 forward the fact that there are a large number of light-coloured 

 butterflies also existing at the higher elevations along with the 

 various melanic species of Erehia. Some of these are almost 

 exclusively white. A list of these pre-eminently xanthochroic 

 species, which I have encountered in the Alps and the Pyrenees 

 between the altitudes of 5500 and 9000 feet, is as follows :— 

 Parnassius apollo, P. deli us, P. mnemosyne, Aporia cratcegi, Pieris 

 hrassiccs, P. rapes, P. napi, P. callidice, P. daplidice,^ Euchloe 

 belia var. simplonia, E. cardamines, Leiicophasia sinapis, Colias 

 paheno, C. phicomone, C. hyale, C. edusa, and Bhodocera rhamni. 

 Some of these I have seen in considerable profusion at the 

 elevations of 7000 and 8000 feet. There are also a considerable 

 number of species whose representatives in the higher zones are 

 of a lighter or brighter coloration than the forms existing at the 

 lower elevations. 



On the other hand, melanism exists at lower levels as well as 

 at the higher ones, such, for instance, as in Polyommatus phlceas 



