﻿have accentuated the development of these 

 substances in certain directions in lines deter- 

 mined by inherent physiological properties, 

 the origin as well as the continuation of 

 which are entirely independent of the prefer- 

 ences of the animal. If insects and birds do, 

 in certain instances, show a preference for any 

 color or color scheme it merely converts an 

 indifferent to a useful property. This is true 

 of attractive as well as of warningcolors. By 

 a recent series of experiments with a number 

 of !tropical plants w^iich have a color scheme 

 resembling that of a poisonous snake, which 

 has been supposed to shield them from attack 

 by animals, it has been found that the degree 

 of hunger of the animals — snails, rabbits, an- 

 telopes, etc.— chiefly determines the choice of 

 food, and that warning devices serve no ac- 

 tual use so far as has been actually demon- 

 stra'^ed. 



It will be found most convenient to discuss 

 the chemical nature and physiological uses of 

 the more prominent coloring substances, under 

 the heads of chlorophyll, etiolin, lipochromes, Enumeration 

 anthocyan or erythrophyll, and various spec- 

 ial colors both red and yellow, to be found 

 within the limits of families, or ecological 

 groups. The manner of occurrence and their 

 universal unstability are such that it has 



of colors 



