of the frog. The mother frog lays her eggs in the water. In due course a new little frog develops from each of these eggs. But the object that develops from them is altogether different from the adult frog. This object is the familiar fish-like tadpole. It finally loses its tail, develops legs, and becomes a frog. Doctor Bölsche discusses the matter as follows:—
"There are reasons on every hand for believing that the frogs and salamanders, which now stand higher in classification than the fishes, were developed from the fishes in earlier ages in the course of progressive evolution. Once upon a time they were fishes. If that is so, the curious phenomenon we have been considering really means that each young frog resembles its fish ancestors. In each case to-day the frog's egg first produces the earlier or ancestral stage, the fish, it then develops rapidly into a frog. In other words, the individual development recapitulates an important chapter of the earlier history of the whole race of frogs. Putting this in the form of a law, it runs: each new individual must, in its development, pass rapidly through the form of its parents' ancestors before it assumes the parent form itself. If a new individual frog is to be developed and if the
