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.
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