i IS EXPERIMENTAL EVOLUTION LECT. 



portance under definite conditions, and may deter- 

 mine life or death in some circumstances, while at all 

 events they must, in every-day life, put the animals 

 which exhibit them in very different positions as 

 regards the struggle for life and success in it. 



Such differences are common in the chemical consti- 

 tution of the different species of the same genus, and 

 the following analysis by Forchammer well illustrates 

 this : 



And again, among different individuals of the same 

 species considerable differences may obtain according 

 to the mode of life, and particularly, as Hermbstaedt 

 has seen, according to food. This fact is well dis- 

 played by the results of Hermbstaedt's experiments 

 on the influence of different manures on the propor- 

 tion of gluten and starch in wheat. Wheat from 

 common soil, neither rich nor poor, has 9-20 per cent, 

 of gluten to 66-69 f starch ; manuring with human 

 urine yields gluten 39- 10 and starch 39*30, and each 



