EFFECTS OF SEXUAL REPRODUCTION. 251 



should not be confounded with that existing in children of very old 

 parents, because the latter arises from another cause, viz., the 

 \veakness existing in the parent due to old age and physical decay. 

 In the one case the weakness exists in both body and mind, in the 

 other case the body is weak but the mind is strong. The first has 

 its cause in immature germ cells ; the second in the inherited inert- 

 ness of the repairing organs of the body, and is sometimes desig- 

 nated as malnutrition. 



If propagation takes place before the bodily growth of the 

 parent is fully completed, and there be no immaturity of the germ 

 cells arising from too rapid cell divisions, then there is a tendency 

 toward increased bodily size of the offspring. This is illustrated in 

 the case of sheep by the largest lambs being produced by rams not 

 fully grown. 2 The explanation of this is that the repairing organs of 

 the parent being functionally active in that condition which pro- 

 duces bodily growth, they produce the same condition in the repair- 

 ing of the germ cells after their divisions. 



BRAIN SIZE AND BRAIN POWER. 



While brain power is, to a considerable extent, dependent upon 

 brain size, yet it is well known that the relative brain power of two 

 persons cannot be determined by measurements of their cranial 

 capacities. A person with a comparatively small brain is very 

 often greatly superior to a person with a much larger brain. This 

 discrepancy may be understood by comparing the causes of brain 

 size and brain power. It has been shown that brain activity causes 

 the brain growth to continue up to the age of twenty-five or thirty, 

 while a lack of activity will cause brain growth to cease at about 

 twenty. If reproduction take place during the latter part of brain 

 (2) Day, The Horse, p. 203. 



