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.
[Illustration: FIG.

13 .-- Sciurus carolinensis.

32 specimens.

Florida.] Mr.Frank E.Beddard has kindly communicated to me some remarkable variations he has observed in the internal organs of a species of earthworm (Perionyx excavatus).