108 THE RIDDLE OF THE UNIVERSE. 



acquired were handed on to posterity by heredity ; in 

 their formation and preservation natural selection 

 plays the same part as in the transformation of every 

 other physiological function. Darwin afterwards 

 developed this fundamental thought in a number 

 of works, showing that the same laws of " mental 

 evolution " hold good throughout the entire organic 

 world, not less in man than in the brute, and even in 

 the plant. Hence the unity of the organic world, which 

 is revealed by the common origin of its members, 

 applies also to the entire province of psychic life, from 

 the simplest unicellular organism up to man. 



To George Romanes we owe the further develop- 

 ment of Darwin's psychology and its special appli- 

 cation to the different sections of ps} T chic activity. 

 The two volumes of his work on evolutionary psychology 

 which were completed are among the most valuable 

 productions of psychological literature. For, con- 

 formably to the principles of our modern monistic 

 research, his first care was to collect and arrange all 

 the important facts which have been empirically 

 established in the field of comparative psychology 

 in the course of centuries ; in the second place, these 

 facts are tested with an objective criticism, and syste- 

 matically distributed ; finally, such rational conclu- 

 sions are drawn from them on the chief general 

 questions of psychology as are in harmony with the 

 fundamental principles of modern monism. The 

 first volume of Romanes's work bears the title of 

 Mental Evolution in the Animal World; it presents, 

 in natural connection, the entire length of the chain 

 of psychic evolution in the animal world, from the 

 simplest sensations and instincts of the lowest animals 

 to the elaborate phenomena of consciousness and 



