CHAPTER I 



THE COLOURS OF ORGANISMS 



Colour Phenomena in General ^ — Distinctions between Pig- 

 mental and Structural Colours — Characters of Structural 

 Colours and their Classification — Production of Light by 

 Organisms (Phosphorescence). 



It is not necessary here to consider in detail the 

 physical aspect of colour. Every one is more or less 

 familiar with the fact that, in general terms, objects 

 appear to us to be coloured because they absorb 

 certain of the elements of white light and reflect 

 the remainder. Thus the substance vermilion 

 appears to us to be red because it absorbs all the 

 components of the incident light except the red, 

 and this it reflects ; it is a fundamental property of 

 vermilion that it possesses this power of selective 

 absorption. Practically all bodies do exercise 

 selective absorption to a greater or less extent, 

 but it is only when the absorption is marked in 

 the visible part of the spectrum that we definitely 

 recognise the bodies as coloured. When such 

 coloured bodies can be employed to impart their 

 own colour to animal or vegetable substances they 



