2f)6 THE INDUCTIONS OF BIOLOGY. 



respect to incident forces ; and that being subject to forces 

 that are more or less unlike, they must become more or less 

 unlike. Hence, no two ova in an ovarura or ovules in a 

 saed-vessel no two spermatozoa or pollen-cells, can be 

 identical. Whether or not there arise other contrasts, there 

 are certain to arise quantitative contrasts ; since the process 

 of nutrition cannot be absolutely alike for all. The repro* 

 ductive centres must begin to differentiate from the very 

 outset. Such being the necessities of the case, what 



will happen on any successive or simultaneous fertilizations ? 

 There will inevitably result more or less unlikeness between 

 the combined parental influences in every instance. Quan- 

 titative differences among the sperm-cells and among the 

 germ-cells, will insure this. Grant that the number of 

 physiological units contained in any one reproductive cell, can 

 rarely if ever be exactly equal to the number contained 

 in any other, ripened at the same time or at a different time ; 

 and it follows that among the fertilized germs produced by 

 the same parents, the physiological units derived from each 

 parent will bear a different numerical ratio to each other in 

 every case. If now the parents are constitutionally alike, 

 that is, alike in the polarities of their physiological units, 

 the variation in the ratio between the physiological units 

 they severally bequeath to the fertilized germs, cannot cause 

 unlikenesses among the offspring. But if otherwise, no two 

 of the offspring can be alike. In every case, the small initial 

 difference in the proportions of the slightly- unlike units, 

 will lead, during evolution, to a continual multiplication of 

 differences : the insensible divergence at the outset, will gener- 

 ate sensible divergences at the conclusion. Possi- 

 bly some may hence infer, that though, in such case, the 

 offspring must differ somewhat from each other and from 

 both parents ; yet that in every one of them there must 

 result a homogeneous mixture of the traits of the two parents. 

 A little consideration shows that the reverse is inferable. If, 

 throughout the process of development, the physiological 



