12 HERBERT SPENCER AND 



the germ-cell from which it was developed. This adult 

 will in turn throw off germ-cells containing physiological 

 units of its own kind, and the round will be completed 

 in the same manner and result in the production of new 

 individuals like to the first. 



But, on the other hand, as the physiological units are 

 not exactly alike among themselves, and as the incident, 

 forces to which the developing germ is subject cannot 

 ever be exactly alike, the reactions between the two will 

 always produce some differences in the adults, and these 

 differences will be due to the changed composition of the 

 physiological units composing them. Hence in every 

 new generation the units will not only be slightly different 

 from those of the parents, but will also be slightly different 

 in the individuals composing the generation, and there- 

 fore in the germ-cells which they in their turn throw off. 

 These germ-cells will therefore give rise once more to 

 slightly different individuals, and so forth. 



It is easy to see that the theory is still more useful in 

 explaining the origin of variations when the mingling of 

 slightly dissimilar physiological units in sexual repro- 

 duction is taken into account. But this need not distract 

 our attention now. 



The most important thing on which to fix our atten tion 

 is that-JSpencer^ theory states that acquired chara cters 

 are transmitted by inher itance. By ^ acquired charact ers ', 

 in tfiis connexion, we~rnean the changes of const itution 

 produc ed in th ej^Jiysiolosi cal unit s by thoir react ion to 

 in cident for ces. 



Darwin, who devoted many years to the study of 

 Variation, agreed to a large extent with Herbert Spencer's 

 view that variations are produced by the action of external 

 forces. 



' Changed conditions act in two ways, directly on the 

 whole organization or on certain parts alone, and in- 

 directly through the reproductive system. In all cases 

 there are two factors, the nature of the organism, which 



