CH. XIV.] LIFE AND MIND. 95 



heard scratching in the wainscot, and it becomes evident that 

 the heterogeneity of the impressions received by an organism 

 is paralleled by the heterogeneity of the adjustments by 

 which it responds to them. The multiplication of the objects 

 and relations of which any organism can take cognizance, 

 involves of necessity a growing complexity in the actions by 

 which it adapts itself to their presence. In civilized man, 

 whose immensely developed cephalic ganglia bear witness to 

 tlie predominance of psychical over physical life, this 

 correlated advance in heterogeneity of correspondence is 

 exemplified in the interdependent progress of science and art. 

 Here again we are carried into the domain of sociology, and 

 this thread must be left to be gathered up with the others 

 when we come to treat of intellectual progress. 



It remains to note that the extension of the correspondence 

 in space and time, and its increase in definite heterogeneity, 

 both heighten the degree of life and add to the ability to 

 maintain life. On the one hand, the more numerous, the 

 more complicated, and the more clearly defined, are the outer 

 relations to which the organism adapts itself, and the longer 

 the interval of time by which the adjustments may be made 

 to forestall external contingencies, the greater will be the 

 number of heterogeneous changes in which life consists. 

 And on the other hand, the greater the number of hetero- 

 geneous changes by which the organism can respond to outer 

 changes, the more easily and surely will life be prolonged. 

 Whence, says Mr. Spencer, " we may clearly see how life 

 and ability to maintain life, are two sides of the same fact — 

 how life is a combination of processes, the result of whose 

 workings is their own continuance." An interesting com- 

 3ientary on this proposition is furnished by Mr. Lankester's 

 recently-published essay on " Comparative Longevity," in 

 which it is shown that high individuation, or the power of 

 responding heterogeneously to external changes, is the chief, 

 Ihough not the sole, factor concerned in producing length 



