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 ancestors of the
whole frog stem were fishes, the first thing to develop from the frog's
egg will be a fish and it will only later assume the form of a frog.

"That is a simple and pictorial outline of what we mean when we speak of
the biogenetic law. We need, of course, much more than the one frog-fish
before we can erect it into a law. But we have only to look around us
and we find similar phenomena as common as pebbles.

"Let us bear in mind that evolution proceeded from certain amphibia to
the lizards and from these to the birds and mammals. That is a long
journey, but we have no alternative. If the amphibia (such as the frog
and the salamander) descend from the fishes, all the higher classes up
to man himself must also have done so. Hence the law must have
transmitted even to ourselves this ancestral form of the gill-breathing
fish.

"What a mad idea, many will say, that man should at one time be a
tadpole like the frog! And yet--there's no help in prayer, as Falstaff
said--even the human germ or embryo passes through a stage at which it
shows the outlines of gills on the throat just like a fish. It is the
same with the dog, the horse, the kangaroo, the duck mole, the bird,
the crocodile, the turtle, the lizard. They all have the same structure.

"Nor is this an isolated fact. From the fish was evolved the amphibian.
From this came the lizard. From the lizard came the bird. The lizard has
solid teeth in its mouth. The bird has no teeth in its beak. That is to
say, it has none to-day. But it had when it was a lizard. Here, then we
have an intermediate stage between the fish and the bird. We must expect
that the bird embryo in the egg will show some trace of it. As a matter
of fact, it does so. When we examine young parrots in the egg we find
that they have teeth in their mouth b