378 The Outline of Science 



particular feature is seen only in his sons, not in his daughters. 

 But the feature may appear in his daughter's sons. 



When the human variant shows a new pattern of a par- 

 ticularly happy kind, we call it "genius"; when the outcome is 

 more dubious we say "crank." And the animal kingdom is full 

 of geniuses and cranks. Our point, however, is just this, that 

 fertilisation offers an opportunity for new permutations and com- 

 binations. If we may compare an inheritance to a pack of cards, 

 each hereditary constituent or "factor" corresponding to a card, 

 then there is in fertilisation a re-shuffling, just as there is in the 

 maturation of the germ-cells an opportunity for cards being lost. 

 We may say, then, that an increased knowledge of the history 

 of the germ-cells since Darwin's day has made it possible to 

 understand how certain kinds of variations may arise. 



If we probe a little deeper, we see the possibility that the 

 stimuli of outside changes, e.g. of climate, may saturate through 

 the organism and provoke the complex germ-cells to change. 

 Thus Professor W. L. Tower subjected potato-beetles at a cer- 

 tain stage of their development to very unusual conditions of 

 temperature and humidity. The beetles themselves were not 

 changed, for these hard-shelled creatures do not lend themselves 

 to external modification. But in a number of cases the offspring 

 of the beetles showed remarkable changes, e.g. in colour and 

 markings. And the offspring of these variants did not revert 

 to the grandparental type. In such a case it looks as if an environ- 

 mental stimulus penetrating through the body serves as the lib- 

 erator or stimulus of variability in the germ-cells. 



It may seem for a moment that this case of the potato- 

 beetles indicates the inheritance of the results of environmental 

 influence. But it must be carefully noticed that the parent 

 beetles showed no modification or acquired character. What 

 happened was that a peculiarity of environment saturated through 

 the body, an*d started a germinal peculiarity, which all biologists 

 are agreed in regarding as heritable. Similarly, persistent alco- 



