EXPRESSION BY HEREDITY. 43 



words only can be said here on the very wide and 

 deep subject of expression by heredity, that is, ex- 

 pression of the conditions of the life-history of the 

 individual, as demonstrated in its offspring, the off- 

 spring showing the effect, or outcome, of forces 

 afferent to one or both parents. 



For our present purpose I think we may classify 

 the phenomena of heredity in terms of certain 

 properties: (1) trophic phenomena; (2) motor, or 

 kinetic, phenomena ; (3) reflex action ; (4) reten- 

 tiveness. We are here dealing solely with the 

 criteria or objective signs of heredity, not with its 

 essential nature. A general review and considera- 

 tion of the facts of heredity enables us to say 

 that we may look upon the four criteria, above 

 mentioned, as the main modes of expression of 

 heredity as a property in the subject. This mode 

 of expression will be discussed in chap. xvi. 



In concluding this chapter we must refer to 

 " expression " in the more limited sense in which 

 the term is commonly used as regards man and 

 animals. " Expression " is a term commonly used 

 to signify the modes in which we judge from out- 

 ward appearances of the mental or physical condi- 

 tion of the individual at the time of observation ; 

 thus we speak of the expression of pain, joy, intelli- 

 gence, hunger, sleepiness, etc. It is our business 

 here to study these expressions, these outcomes or 

 ejecta, these uniform objective concomitants of the 

 hidden conditions intelligence, hunger, sleepiness, 

 consciousness, feebleness. It is not for us here to 

 study subjective conditions or feelings and states 



