112 



THE WORLD OF LIFE 



CHAP. 



" Every organism varies in respect of all its characters, whatever be 

 their nature. The amount of this variation differs greatly, but it is 

 always present in a greater or less degree." 



And again, referring to a diagram showing the variations of 

 a squirrel, he says : 



" Variation of a similar nature though of a varying degree is 

 present in all organisms, to whatever class of the animal or 

 vegetable kingdom they belong." 



Referring to the diagram of human stature at p. 108, it 

 is found that about half the whole number measured vary a 

 little more than 2 inches above or below the mean, or a 

 little more than 3 per cent of the mean height. This is 

 termed the percentage of mean error, and Mr. Vernon gives 

 us an interesting table of the same percentage for different 

 parts of the body derived from very large numbers of 

 measurements of different races of men. It is as follows : 



Nose length . 



,, breadth . 



height . 

 Forehead height 

 Under-jaw length 

 Mouth breadth 



Here we see that the different parts of the human body vary 

 more, proportionally, than does its whole height ; and we 

 must always remember that these variations are all, to a 

 large extent, independent of each other, just as we saw was 

 the case with those parts shown in the bird diagram. 



Again we must lay stress upon the fact that every part 

 of every organism, outside or inside, important or insignifi- 

 cant, is subject to a similar and often more pronounced 

 amount of variation, as numerous examples quoted in Mr. 

 Vernon's book amply prove. So that we are fully justified 

 in accepting as a demonstrated fact, that the whole structure 

 of every organism, in every stage of its growth or develop- 

 ment, varies in its different individuals, each one in a somewhat 

 different manner, and to such a large extent as to afford the 

 amplest store of material for modification and development 

 in any direction that may be required. 



