210 DE GENERA TION 



It is a physiological demand that constant, regular, not 

 excessive use of any organ is absolutely necessary to its 

 maintenance. Indeed, the stimulus to which it responds is 

 undoubtedly the influence to which an organ owes its origin 

 and its gradual evolution. 



Let us dwell somewhat farther on the eye. 



Weismann says : " Short sight, it is true, can be acquired, 

 but then it is not inherited, as I at least believe myself 

 bound distinctly to suppose. In my opinion, we owe the 

 extensive prevalence of shortsightedness, not merely to the 

 excessive straining of the eyes and to the continual observa- 

 tion of near objects, but to pammixis, the cessation of natural 

 selection in this direction ; for we are as much subject to 

 the effects of these causes as all other organisms. As it is 

 pretty nearly indifferent in the present state of society 

 especially since spectacles were invented whether the in- 

 dividual sees somewhat farther or a somewhat less distance, 

 the organ of sight has come under the action of pammixis." 



That Weismann's conclusion is possibly partially true also 

 in this instance we readily admit. But proof is wanting 

 of the principal assertion, that short sight is not simply 

 hereditary. The question would have to be tested accurately 

 by the oculists with respect to Weismann's statements, to 

 be treated statistically. He himself does not speak very 

 decidedly on the point. 



He says further, moreover, in connection with this same 

 subject, that the deterioration of bodily advantages in us, in 

 comparison with our forefathers, is to be considered in rela- 

 tion to the high development of our intellect. But this 

 intellect can surely only have been gradually acquired and 

 transmitted by our forefathers. It depends upon experience, 

 which certainly cannot be produced by variability of the 

 germ-plasm. I shall have occasion subsequently to consider 

 this question at greater length. 



