Variation and Natural Selection. 63 



standing the law of hereditary persistence, variations 

 should occur in the offspring of animals. At the same 

 time, it must be remembered that the occurrence of varia- 

 tions is not and cannot be the result of mere chance ; but 

 that all such variations are determined by some internal or 

 external influences, and are thus legitimate and important 

 subjects of biological investigation. In the next chapter 

 we shall consider at some length the phenomena of heredity 

 and the origin of variations. Here we will accept them 

 without further discussion, and consider some of their con- 

 sequences. But even here, without discussing their origin, 

 we must establish the fact that variations do actually occur. 



Variations may be of many kinds and in different 

 directions. In colour, in size, in the relative develop- 

 ment of different parts, in complexity, in habits, and in 

 mental endowments, organisms or their organs may vary. 

 Observers of mammals, of birds, and of insects are well 

 aware that colour is a variable characteristic. But these 

 colour-variations are not readily described and tabulated. 

 In the matter of size the case is different. In Mr. Wallace's 

 recent work on " Darwinism " a number of observations 

 on size-variations are collected and tabulated. As this is 

 a point of great importance, I propose to illustrate it some- 

 what fully from some observations I have recently made of 

 the wing-bones of bats. In carrying out these observa- 

 tions and making the necessary measurements, I have had 

 the advantage of the kind co-operation of my friend Mr. 

 Henry Charbonnier, of Clifton, an able and enthusiastic 

 naturalist.* 



The nature of the bat's wing will be understood by 

 the aid of the accompanying figure (Fig. 12). In the fore 

 limb the arm-bone, or humerus, is followed by an elongated 

 bone composed of the radius and ulna. At the outer end 

 of the radius is a small, freely projecting digit, which 

 carries a claw. This answers to the thumb. Then follow 

 four long, slender bones, which answer to the bones in the 



* I have also to thank Mr, Edward Wilson for kindly giving me the 

 measurements of three or four bats in the Bristol Museum. 



