CONTENTS xiii 



ditions — The origin of the eye and ear from the skin — The 

 origin of the central nervous system in the skin — The origin 

 of the nerves in (a) a primitive connection between the 

 central system and muscle ; and (b) an equally primitive con- 

 nection between the internal movements and the governing 

 central system ; and (c) a correlation between (a) and (6) . 140 

 The stiffening of these inward and outward responses into habit 

 and tradition — The evolution of more complex responses 

 based upon a groundwork of muscular and sensitive re- 

 sponse — The greater strenuousness of life on land and in 

 air has led to the evolution of complex instincts — The 

 power of profiting by experience — The domestication of 

 animals, and its far-reaching effects on man's social life . 144 



CHAPTER VIII 



THE COLOURS OF ANIMALS 



The primary meanings of animal colours : 



Colours the outcome of inward processes — The relation 

 of animal pigments to light — Exposed surfaces of the 

 body more deeply coloured than shaded ones — Experi- 

 mental evidence on the colouring action of light — The 

 bleaching effect of darkness — Agreement between plant 

 foliage and animals in colour distribution — The green 

 pigment of plants concerned in nourishment — The red pig- 

 ment of blood and muscle a respiratory substance, and only 

 secondarily a decorative one — The relation between the 

 two in chemical composition — Loss of green pigment in 

 parasitic plants ; temporary loss in minute flagellate 

 organisms when supplied with organic food, reacquire- 

 ment of the green colour under inorganic nourishment — 

 Nature of these Flagellata : a connecting-link between 

 animals and plants — The adoption of solid food and the 

 origin of muscle gave the animal branch of this family 

 greater facilities for distribution and involved more efficient 

 oxidation — Evolution of the blood pigments . . . 149 



The evolution of red and yellow fatty pigments — Wide 

 distribution of these in animals and plants — Association of 

 these pigments with stores of reserve food — Association 

 of fat with these pigments in the skin and other tissues 

 of the ^Esop prawn — Evidence for the formation of this 



