ABSTRACT
The inheritance in the female of uterine modifications might in itself be sufficient cause to account for many species differences on the basis of resulting modifications in the developmental processes under a changed environment. Many similar examples of functional change, or functions wechsel, as the German zoologist, Anton Dohrn, expressed it, are found among higher vertebrates, although the actual genesis of such modifications is quite unknown. Among the mammals there are various types of specialized or modified feet in which the one common feature is the reduction in number of digits or toes below the primitive five-toed condition. The toe arrangement is less modified in the dog than in the guinea-pig, and the genetics of the reappearing great toe in dogs is correspondingly much simpler than the reappearance of the small toe and the thumb in the guinea-pig.
