As it seems to me, the leading facts in embryology, which are second to none in importance, are explained on the principle of variations in the many descendants from some one ancient progenitor, having appeared at a not very early period in life, and having been inherited at a corresponding period. Embryology rises greatly in interest, when we look at the embryo as a picture, more or less obscured, of the progenitor, either in its adult or larval state, of all the members of the same great class.[1]
Yet poor Chambers is reproached for "baseless speculation" because, looking upon facts accepted by all the competent embryologists of his time, he saw in them the meaning that Darwin afterwards saw, and that so great a mind as LyelPs had been unable to see. In the third edition of the "Vestiges," 1845, he wrote:
First surmised by the illustrious Harvey, afterwards illustrated by Hunter in his wondrous collection at the Royal College of Surgeons, finally advanced to mature conclusions by Tiedemann, St. Hilaire and Serres, embryotic development is now a science. Its primary positions are. . . (2) that the embryos of all animals pass through a series of phases of development, each of which is the type or analogue of the permanent configuration of tribes inferior to it in the scale.
And in this Chambers found one of his chief evidences of transformation of species. Elsewhere in this edition he devotes several pages to the elaboration of the argument from recapitulation in the case of the brain. "Taking as a basis the scale of animated nature as presented in Dr. Fletcher's 'Rudiments of Physiology,'" he points out "the wonderful parity observed in the progress of creation, as presented to our observation in the succession of fossils, and also in the fœtal progress of one of the principal human organs."[2]
8. The Argument from Rudimentary Organs.—In his "Lectures on the Phenomena of Organic Nature," 1863, Huxley mentions as illustrations of this type of evidence the fœtal teeth of the whalebone whale, the rudimentary toes in the horse's leg, the rudimentary teeth in the upper jaw of the calf. He concludes:
Upon any hypothesis of special creation, facts of this kind appear to me entirely unaccountable and inexplicable; but they cease to be so if you accept Mr. Darwin's hypothesis, and see reason for believing that the whalebone whale and the whale with teeth in its mouth, both sprang from a whale that had teeth, and that the teeth of the total whale are merely remnants—recollections if we may so say—of the extinct whale. . . . The existence of identical structural roots, if I may so term them, entering into the composition of widely different animals, is striking evidence in favor of the descent of those animals from a common original.
But from the same facts Chambers had argued to the same conclusion nearly a score of years earlier.
The baleen of the whale and the teeth of the land mammals are different organs. The whale in embryo shows the rudiments of teeth; but these not being wanted, are not developed, and the baleen is brought forward instead.
