Chap. I. COLOUKS OF TROPICAL INSECTS. 21 



It holds good in all families that the two sexes of the 

 more brilliantly-coloured kinds are seldom equally 

 beautiful ; the females being often quite obscure in 

 dress. There is a very large number of dull-coloured 

 species in tropical countries. The tropics have also 

 species in which the contrast between the sexes is 

 greater than in any species of temperate zones ; in some 

 cases the males have been put in one genus and the 

 females in another, so gTeat is the difference between 

 them. There are species of larger size, but at the 

 same time there are others of smaller size in the same 

 families in tropical than in temperate latitudes. If 

 we reflect on all these facts, we must come to the con- 

 clusion, that climate, to which we are naturally at 

 first sight inclined to attribute much, has little or no 

 direct influence in the matter. Mr. Darwin was led to 

 the same conclusion many years ago, when comparing 

 the birds, plants, and insects of the Galapagos islands, 

 situated under the equator, with those of Patagonia 

 and Tropical America. The abundance of food, the 

 high temperature, absence of seasons of extreme cold 

 and dearth, and the variety of stations, all probably 

 operate in favouring the existence of a greater number 

 and variety of species in tropical than in temperate 

 latitudes. This, perhaps, is all we can say with regard 

 to the influence of climatal conditions. The causes 

 which have produced the gi'eat beauty that astonishes 

 us, if we really wish to investigate them, must be sought 

 in other directions. I think that the facts above men- 

 tioned are calculated to guide us in the search. They 

 show, for instance, that beauty of form and colour is 



