SPENCER'S CONTRIBUTIONS 



of the importance of this idea the reader may con- 

 sult such a standard work as that of M. Yves 

 Delage on UHGr6dit&. But since that work was 

 written there has come into prominence the long- 

 forgotten research of Mendel, to which reference 

 has been made in a previous chapter. Compari- 

 son of the views of Mendel's contemporary follow- 

 ers, such as De Vries and Bateson, will show that 

 the "physiological unit" of Spencer is the logical 

 foundation of the modern theory of heredity, which 

 has come into its own within the last decade. In 

 this relation especial interest appears to me to 

 attach to the recent development of the micro- 

 scope by Gordon and others. It is now possible 

 to study the cell under a power of ten thousand 

 diameters; and calculation of molecular size by 

 Lord Rayleigh, Lord Kelvin, and others appears 

 to show that the real unit of life may prove to be 

 actually visible, if not now, at any rate in the not 

 very remote future. 



On the border - line between biology and psy- 

 chology, but legitimately to be treated here, is the 

 question of the evolution of the nervous system 

 and the differentiation of the senses of man. This 

 I have already discussed in a previous volume, 1 

 and here I would rather refer to the inference which 

 may be drawn from the fact, broadly stated, that 

 the human brain* and central nervous system 



1 See the essay entitled "The Evolution of Sense," in The 

 Cycle of Life, or, much better, Tyndall's memorable "Bel- 

 fast Address," delivered before the British Association in 1874. 



