330 THE INDUCTIONS OF BIOLOGY. 



sion or simultaneously;, are separated from the same parent, 

 can never be exactly alike; nor can the sperm-cells which 

 fertilize them. When treating of the instability of the 

 homogeneous {First Principles, § 149), we saAv that no two 

 parts of any aggregate can be similarly conditioned with re- 

 spect 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 ovarium or ovules in a 

 seed-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? 

 Inevitably unlikenesses between the respective parental in- 

 fluences must result. Quantitative 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 physiolo- 

 gical units derived from them respectively will bear a dif- 

 ferent numerical ratio to each other in every case. If the 

 parents are constitutionally quite alike, the variation in the 

 ratio between the units they severally bequeath, 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 differ- 

 ences. The insensible divergence at the outset will gene- 

 rate sensible divergences at the conclusion. Possibly 

 some may hence infer that though, in such case, the off- 

 spring must differ somewhat from each other and from both 

 parents, yet that in every one of them there must result a 



