1 INTRODUCTION 



measured by time, by far the longer portion : but it is really 

 a mere lingering over the final stage of maturity : as measured 

 by development, the animal's career at the moment of birth 

 is very near its termination. The various tissues and organs 

 are set hard in very nearly their final shape : the morpho- 

 logical polarisation can no longer be altered except in minute 

 details. Now it is in this developmentally late stage of an 

 animal's career that modifications due to environment 

 are chiefly acquired. How, then, is it to be supposed that 

 such modifications should leave a deep organic impress ? 



Supposing once more we shift attention from the life of 

 the individual to the life of the race ; and regard a species 

 as synonymous, not with the mature individuals composing 

 it, but with the germ-plasm from which they sprout. This 

 germ-plasm is potentially immortal. Countless miUions of 

 years ago that same germ-plasm which we now carry in our 

 bodies was already in existence : but it had not then the 

 power of budding forth a mammal. It had originally 

 no power of budding forth anything at all. It was 

 a protozoon, and perpetuated itself as it still does 

 by division of the one cell into two. But gradually new 

 qualities were added to this aboriginal germ-cell. The 

 daughter-cells were not in all cases completely separated 

 from their parent, and excrescences came to be formed on 

 the germ-cell, as the evolution of the metazoa was attained. 

 It is these excrescences only that are mortal. In the progress 

 of evolution, the character of the excrescence growing from 

 the germ-cell has greatly altered ; until in some cases it 

 has assumed the shape of a mammal. But the germ-cell of 

 the mammal is just the same germ-cell as that which existed 

 at the outset of evolution. It has innumerable times been 

 divided in half, and one half has been cast away : but there 

 has been no other discontinuity either in the individuality 

 or substance of the cell. 



Hence we may regard the germ-cell of a mammal as 

 having lived and preserved its personality for myriads of 

 years. During that time it has greatly changed the kind 



