66 
DARWINISM 
CHA1>. 
and compared, and thus 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 group, 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 
wild 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 with 
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 great 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 wing 
or tail feathers of birds 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 
