504 Mr. G. Lewis' supplementary note on the 



it has been said, that after colour has appeared in a 

 • species, by some cause not explained, sexual selection 

 can continue to improve it. But a truer explanation of 

 insect-colour, to my mind, would be, if it could be shown 

 that by little and little, in minute gradations, through 

 long periods, sun-rays are the cause of it. And this, I 

 think, is the origin of it, through what may be termed 

 Photoplasticity, a photoplastic process by which the 

 various rays or wave-movements from the sun impress 

 living organisms with the structure necessary for colour. 

 What we call bright colour does not exist in obscurity ; 

 light is necessary to appreciate it, and is, I think, the 

 factor which produces it, and that nocturnal insects are 

 black because they are not affected by the direct rays 

 from the sun. 



Professor Tyndall, in 'Forms of Water,' 1878, says of 

 the wave theory of light, ''It is because of its com- 

 petence to explain all the phenomena of light that the 

 wave theory now receives universal acceptance on the 

 part of scientific men." So the theory of the mechanical 

 action of light may be accepted as the cause of colour, 

 if it is sufficient to explain the phenomena of colour; 

 and it is the object of a portion of this short note 

 to bring forward a few facts tending, as I think, to 

 prove it. 



Damaster hlaptoides is a nocturnal insect ; it is a 

 night-rover, and during the day secretes itself in the 

 rotten touchwood of old trees, remaining always well 

 out of the light. Noctnce are not nocturnal in this sense, 

 as they are exposed to certain rays of light during the 

 day. Some, e. g. Aplecta tincta and others, possess a 

 colour called a protective colour, and rest on mottled 

 moss-grown bark in the daytime, and it is then their 

 colours are originated, not during flight, for their tints 

 are not then visible, and it is on the upper wings alone 

 that maculation appears. If we believe that there has 

 been, and still is, a continuous modification of species 

 throughout Nature, we must consider that the Noctiue 

 and the lichens have grown together, each out of some 

 older form, sufficiently long to have been more or less 

 modified side by side, as the contingencies of their 

 existence dictated change ; and, as their colours assimi- 

 late, we must, I think acknowledge, that they have 

 acquired them by the same natural processes ; say, for 

 instance, in the subdued light-rays of an umbrageous 



