INTRODUCTION 3 



through millions of years, yet we are daily reminded of 

 its evanescent nature. Its power of reproducing itself 

 according to type, none can doubt, yet no two individuals 

 are exactly alike. 



The purely physical phenomena of life, to be rightly 

 appreciated, must always be considered in relation to the 

 psychical phenomena which are the soul of life. These 

 subtle and intangible forces cannot be experimented with 

 in the laboratory, or expressed in formulae ; we cannot 

 denote their strength in horse-power. Just as the physi- 

 cal manifestations of life begin with lowly types, so 

 the psychical begin, and they gather strength and 

 complexity with the bodies they pervade. These mani- 

 festations we call behaviour, and in their more intense 

 developments, " emotions." 



These emotions present an infinite range of variety in 

 the higher animals, and they attain their maximum of 

 intensity wherever the reproductive activities are con- 

 cerned. The part which these activities play in con- 

 trolling behaviour is by no means always apparent, and 

 is commonly not even suspected. Even man himself is 

 subject to this control. And it is this fact which lifts the 

 " Courtship " of the lower animals out of the category 

 of merely curious phenomena. For the springs of his 

 conduct, his behaviour and " emotions " under varying 

 circumstances, can only be understood, and even then but 

 imperfectly, by comparison with other creatures lower in 

 the scale, so far, of course, as comparison is possible. 

 '^ This line of inquiry, then, takes one back to the simplest 

 living things, among which there is neither marrying nor 

 giving in marriage, neither birth nor death. Life is re- 

 duced to its simplest terms — a speck of animated jelly is 

 all that confronts one, and this is only to be seen under a 



