HEREDITY. 



INTRODUCTION. 



PHYSIOLOGICAL HEREDITY. 



HEREDITY is that biological law by which all beings endowed 

 with life tend to repeat themselves in their descendants : it 

 is for the species what personal identity is for the individual. 

 By it a groundwork remains unchanged amid incessant variation ; ' 

 by it Nature ever copies and imitates herself. Ideally con- 

 sidered, heredity would simply be the reproduction of like by like. 

 But this conception is purely theoretical, for the phenomena of 

 life do not lend themselves to such mathematical precision : 

 the conditions of their occurrence grow more and more complex in 

 proportion as we ascend from the vegetable world to the higher 

 animals, and thence to man. 



' Man may be regarded either in his organism or in his 

 dynamism : in the functions which constitute his physical life, or 

 in the operations which constitute his mental life. Are both of 

 these forms of life subject to the law of heredity? "are they subject 

 to it wholly, or only in part ? and, in the latter case, to what extent 

 are they so subject? 



c The physiological side of this question has been diligently 

 studied, but not so its psychological side. We propose to supply 

 this deficiency in the present work.'' But the hereditary trans- ' 

 mission of mental faculties considered in its phenomena, its laws, 

 its consequences, and especially in its causes is so closely con- 

 nected with physiological heredity, that we are compelled to 



