66 DARWINISM chap. 



and compared, and tlnis the materials for determining the 

 question of their variability in a state of nature are compara- 

 tively scanty. The fact that our domestic animals belonging 

 to this gToup, especially dogs, present extreme varieties not 

 surpassed even by pigeons and poultry among birds, renders it 

 almost certain that an equal amount of variability exists in the 

 ■n^ld state ; and this is confirmed by the example of a species of 

 squirrel (Sciurus carolinensis), of which sixteen specimens, all 

 males and all taken in Florida, were measured and tabulated 

 by Mr. Allen. The diagram here given shows, that, both the 

 general amount of the variation and the independent variability 

 of the several members of the body, accord completely vnth. 

 the variations so common in the class of birds ; while their 

 amount and their independence of each other are even greater 

 than usual. 



Variation in the Internal Organs of Animals. 



In case it should be objected that the cases of variation 

 hitherto adduced are in the external parts only, and that 

 there is no proof that the internal organs vary in the same 

 manner, it will be advisable to show that such varieties also 

 occur. It is, however, impossible to adduce the same amount 

 of evidence in this class of variation, because the gi'eat labour 

 of dissecting large numbers of specimens of the same species 

 is rarely undertaken, and we have to trust to the chance 

 observations of anatomists recorded in their regular course of 

 study. 



It must, however, be noted that a very large proportion of 

 the variations already recorded in the external parts of 

 animals necessarily imply corresponding internal variations. 

 When feet and legs vary in size, it is because the bones vary ; 

 when the head, body, limbs, and tail change their proportions, 

 the bony skeleton must also change ; and even when the wdng 

 or tail feathers of bii-ds become longer or more numerous, 

 there is sure to be a corresponding change in the bones which 

 support and the muscles which move them. I will, however, 

 give a few cases of variations which have been directly 

 observed. 



Mr. Frank E. Beddard has kindly communicated to me 

 some remarkable variations he has observed in the internal 



