154 WORLD-POWER AND EVOLUTION 



proportions. In cold weather, however, the abnormalities in- 

 creased, and came much nearer to following the Mendelian laws. 

 Therefore some experiments were tried similar to those already 

 described in respect to butterflies. The eggs were placed in a 

 temperature of about 50°F instead of about 70" which was the 

 usual condition in the experimental rooms. The results of the 

 best experiment are shown in the following table; 



The important part of this table is the right-hand column. It 

 shows that when the eggs were cooled at a very young stage all 

 of those that hatched were abnormal. If there was some delay 

 in cooling the eggs, the proportion of abnormality decreased until 

 an average of about 10 per cent was reached. In other words, 

 if the eggs were not cooled till after the fourth day there was no 

 more effect than when they were not cooled at all. Consider what 

 this means. Suppose that for some unexplained reason this 

 mutant happened to arise in nature. If the flies were living in a 

 climate where the temperature rarely fell to 50° during their 

 breeding period the mutation would doubtless soon die out. If 

 the climate should change, however, so that cool waves came fre- 

 quently during the summer and lasted three or four days, the 

 mutant might thrive so that before long it would become as 

 abundant as the old species. Thus a new species or even a new 

 genus with an extra pair of legs might conceivably arise. This 

 would be the more likely to happen because Miss Hoge's experi- 



