512 Mr. G. Lewis' supijlevientary note on the 



I must refer again to the Carahidce and Buprestidce. In 

 the first family we have noticed that bright species occur 

 in the Spanish mountains in a brilHant sun of a dry 

 atmosphere ; colour here is the effect of direct sun-rays, 

 because it is the upper surface alone which is brilliant ; 

 Carahidce being on the under surface black. And another 

 thing requires special notice, — the elytra are most fre- 

 quently of a different tint to the head and thorax. As 

 the insect rambles, the abdomen is carried on in the 

 same parallel line, but the head and thorax move as the 

 animal feeds or runs, and they present to the sun a 

 different superficies, such as has been noticed in the 

 fiight of butterflies, and the result is two distinct colours. 

 Many of the Geodeijhaga have the elytral margin alone 

 brilliant, and this is the surface which receives the full 

 force of direct solar-rays ; and it is in this spot that 

 colour in many species evidently begins, for even in 

 bright species colour is brightest there. In the second 

 family we find the under surface of the body is as bril- 

 liant as the u]3per, except in the Madagascar species, 

 when the under surface has the greater brilliancy. 



Professor Tyndall tells us : — " The heating of the 

 tropical air by the sun is indirect. The solar beams 

 have scarcely any power to heat the air through which 

 they pass ; but they heat the land and the ocean, and 

 these communicate their heat to the air in contact with 

 them. The air and the vapour start upwards charged 

 with the heat thus communicated to them." Here is an 

 upward movement, and in the tropics where this takes 

 place we find insects which sit on foliage are brilliant 

 beneath, as the heat-rays, moving upwards, affect the 

 under parts of the beetles in the same way as direct 

 rays affect th,e Spanish Carabi. There is nothing essen- 

 tial in the direct sun-rays of the tropics to create colour 

 quicker or in a greater degree than in temperate zones, 

 but the heat of the air and the moisture there promotes 

 a more vigorous growth in the organisms on which it 

 acts ; and perhaps the sun-ray sculpture is rendered 

 permanent sooner there. For there is little doubt that 

 species are less permanent in the tropics than in tempe- 

 rate zones ; that is to say, they are more impressible and 

 liable to quicker modification in the same ratio as their 

 vital energy is greater. The winter in our own lati- 

 tude reduces the growing period of organic life by perhaps 

 one-half, and the feebleness of growth during the other 

 six months lessens it much more. 



