GEOGRAPHICAL DISTRIBUTION OF INSECTS. 281 



the production of any region, that these are influenced as much 

 by the mean temperature of the coldest and hottest months ; 

 that often, countries, possessing the same mean annual tem- 

 perature, differ surprisingly in their mean summer and mean 

 winter temperatures ; that, as we approach the equator, the 

 temperature of elevated districts will become more and more 

 uniform throughout the year, and less resemble that of the low 

 grounds of higher latitudes, where the mean temperature is the 

 same. Nor should he omit to observe the nature of the soil, 

 the humidity or dryness of the atmosphere, and the generally 

 clear or cloudy state of the sky, which so much influences 

 vegetation. 



In speaking of the generally cloudy state of the sky, I allude 

 more particularly to parts where, as on the coast of Peru, 

 or in the neighbourhood of Turbaco, in Colombia, the sky is 

 almost always covered with a sort of haze, which of course 

 diminishes much the effect of the sun's rays. It would be 

 highly interesting to observe carefully the insects of parts situ- 

 ated under such a sky, because thence we might be enabled to 

 form many interesting conjectures as to the effect of light upon 

 their colouring. Without doubt the greater intensity of light 

 in the equatorial regions adds to its richness and brilliancy. 

 M. Boisduval informs us that Urania Rhiphceus, if disclosed 

 from the pupa in the shade, never attains its full beauty, the 

 colouring always being fainter than when the wings are ex- 

 panded in the sun. 



Latreille, in his " Introduction a la Geographie Generale 

 des Arachnides et des Insectes," observes, " Je crois pouvoir 

 assurer que l'augmentation de la lumiere tend a convertir le 

 jaune en rouge ou en orange, et que sa deperdition fait passer 

 ce jaune au blanc. Ce fait s'applique aussi a des coquilles 

 h'Helix nemoralis, ou la livree, qui dans nos climats a le fond 

 jaune est rouge ou rougeatre en Espagne : des qu'en allant 

 du nord au midi Ton arrive a l'lle de Teneriffe, Ton s'apercoit 

 deja que notre papillon du chou (Papilio Cheiranthi, Ilubn.) et 

 celui qu'on nomme le Vulcain {Atalatita) ont eprouve une modi- 

 fication dans leurs couleurs." This may all be perfectly true, 

 but there follows a sentence which, I must confess, a little 

 staggers me; and if M. Latreille brings forward the fact there 

 stated to support his theory, that the diminution of light "fait 

 passer ce jaune au blanc," nothing could be more unfortunate, 



NO. III. VOL. II. o o 



