Embryology teaches us that the eggs from which all animal forms evolve are all practically alike so far as one can ascertain by microscopic examination, no matter how diverse may be the forms which will evolve from them, and this resemblance is maintained even when the embryo of the higher forms begins to manifest traces of its future form.  Von Baer, the German scientist, was the first to note this remarkable and suggestive fact.  He stated it in the following words:  “In my possession are two little embryos, preserved in alcohol, whose names I have omitted to attach, and at present I am unable to state to what class they belong.  They may be lizards, or small birds, or very young mammals, so complete is the similarity in the mode of the formation of the head and trunk in these animals.  The extremities, however, are still absent in these embryos.  But even if they had existed in the earliest stage of their development, we should learn nothing, for the feet of lizards and mammals, the wings and feet of birds, no less than the hands and feet of man, all arise from the same fundamental form.”

As has been said by Prof.  Clodd, “the embryos of all living creatures epitomize during development the series of changes through which the ancestral forms passed if their ascent from the simple to the complex; the higher structures passing through the same stages as the lower structures up to the point when they are marked off from them, yet never becoming in detail the form which they represent for the time being.  For example, the embryo of man has at the outset gill-like slits on each side of the neck, like a fish.  These give place to a membrane like that which supersedes gills in the development of birds and reptiles; the heart is at first a simple pulsating chamber like that in worms; the backbone is prolonged into a movable tail; the great toe is extended, or opposable, like our thumbs, and like the toes of apes; the body three months before birth is covered all over with hair except on the palms and soles.  At birth the head is relatively larger, and the arms and legs relatively longer than in the adult; the nose is bridgeless; both features, with others which need not be detailed, being distinctly ape-like.  Thus does the egg from which man springs, a structure only one hundred and twenty-fifth of an inch in size, compress into a few weeks the results of millions of years, and set before us the history of his development from fish-like and reptilian forms, and of his more immediate descent from a hairy, tailed quadruped.  That which is individual or peculiar to him, the physical and mental character inherited, is left to the slower development which follows birth.”