94 EVOLUTION AND MAN S PLACE IN NATURE 



disposition are transmitted from one generation to 

 another. 1 This inclusion of mental disposition 

 shows the facility with which a vast inference may be 

 accepted and stated. Even in face of the gigantic 

 undertaking of explaining organic differentiation, it 

 is assumed that the whole manifestations of activity, 

 even intellectual and rational, are to be traced to the 

 ovum in which physical life-movement has its rise. 

 That the germ-cell produces all that belongs, to 

 organic life, may be accepted as a maxim ; but science 

 is still a long distance away from any summary of 

 evidence which can support a wider conclusion. It 

 may not be unwise, therefore, to subdivide the vast 

 subject, postponing the problem as to mental dis 

 position, as well as the still higher phenomena of 

 rational life. We prefer here, at the outset, to deal 

 exclusively with heredity in its earliest form, as 

 beginning in organism, and concerned with the 

 reproduction of structure and function, characteristic 

 of a given species. 



Taking the problem in this form, there are two 

 available points of observation, that which looks 

 towards the mature organism, thence attempting to 

 think backwards to the germinal form ; and that which 

 contemplates the germ-cell, tracing thence from the 

 earliest chemical and molecular movements, the 

 elaborate course of differentiation. Darwin, as a 

 biologist, trained in comparative observation of form, 

 colour, and functions, naturally prefers the stand 

 point supplied by the mature life, leaning upon 

 evidence of variation scattered over the annals of 

 natural history. Weismann, as a histologist, skilled 

 in microscopic research, naturally passes to the cell 



1 Essays on Heredity, vol. i. p. 167. 



