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lizards have a body too narrow to admit of the use of two lungs, and accordingly we find them with only one active lung and the remnant of another. So, too, the horse (as will be seen in the following chapter) has rudiments of two toes on each side of the foot, besides the one toe on which the hoof is set, which alone is of use to him.
In the above instances, it is plain enough that the animal would have gained in the struggle for existence by losing the organs which have in each case become aborted ; and we may be sure that natural selection would operate powerfully to perpetuate any variations which at first tended toward bringing about the degenerated condition. Multitudes of instances are known; but only a few of the most curious and instructive can here be cited. The Greenland wliale, when full-grown, has no teeth; but in the embryonic condition it has teeth in both jaws. Calves, before birth, have eye-teeth and cuttingteeth in the upper jaw; the boa-constrictor has rudiments of hind-legs and of hip-bones; many birds (as the ostrich) have only rudiments of wings; and among insects we find all the stages, from the possession of two pairs of wings fully developed, to the complete absence of wings.
It will be noticed, from what has been stated,
that some of these undeveloped organs show themselves only during the embryonic state : and there is one most striking fact of this kind; namely, that all vertebrate animals above fishes pass through one embryonic stage, during which there appear four distinct arches, or pairs of semi-arches, of gristle on the neck, corresponding exactly in position and mode of growth to the gill-arches of fishes. These gill-arches in fishes are well known to every boy who has worked a fish-hook loose from the slender hoops on which the red gill-fringes are supported.
Fig. 15. - Embryonic Fishes.
At A in the figure is represented the embryonic fish at an early stage of its growth; the gill-arches being at g. In B and C the more
fully developed animal is seen, with the gill clefts and arches represented at g. An embryonic turtle, chicken, or rabbit so closely resembles the early condition of a very young fish, that the same figure A would fairly represent them all.
But what does the presence of these rudiments in all vertebrates (man included) in the early stages of growth mean? What can it mean, except that all vertebrate animals must look back to a common ancestry ? For the facts of embryology and the existence of rudimentary organs, no more than two explanations can be offered. Either the possession of common characteristics in the whole series of animal sub-kingdoms, and the circumstance that each animal in the successive periods of its early life-history passes through stages in which it is extremely similar to full-grown individuals of lower forms, indicate a relationship on the part of the higher form to the lower ones, or they do not. In the latter case we must conclude that these resemblances were deliberately created for some incomprehensible purpose. But then we should be forced to attribute imperfection to the plans of the Creator, since we find that in many instances the resemblance of the early stages of an animal to lower forms is highly disastrous to the animals.
The free-swimming stage through which young oysters, for example, pass, is the cause of a very large proportion of every generation of young becoming destroyed; so that it is only by their extraordinary breeding-powers that the nunber of oysters is maintained. So, again, the retention of embryonic, rudimentary organs and condicions after birth is the cause of many disagreeable and injurious monstrosities. Or an undeveloped organ may, while of no use in itself, become the seat of disease; notably so in the case of the abortive human tail, the coccyx, a little series of three, four, or five joints at the end of the backbone, which are by no means indispensable, but which sometimes become the seat of so painful a neuralgic condition, that they have to be removed by amputation.2
And again: there is found in man a slender, blind tube (the worm-shaped appendage) attached to the region where the large and the small intestine are joined together. In many of the lower animals, as, for instance, in the apes, which live on vegetable food, this tube is a large and useful part of the intestine; but in man, in its abortive condition it is apparently
1 Such, for example, as hare-lip.
2 Ziemssen's Cyclopædia of Practical Medicine, vol. x. pp 559, 560.
worse than useless, since it not infrequently becomes the cause of death from the lodgement of any small substance (as, for example, a raisinseed or a cherry-stone) in the appendage. Such a mishap as this lodgement is always likely to be followed by violent ir.flammation, from which, as just stated, death often results.
In summing up the embryological evidence as here recited, it will be remembered that all of the sub-kingdoms of animals above the lowest one have been shown to resemble each other in a most interesting way by exhibiting, first a mulberry-stage, and then a gastrula-stage, at an early period of their life history. All vertebrates have been shown to exhibit their common origin from some fish-like form by the possession of gill-arches in the embryo. A few other abortive organs have been mentioned, among them some so injurious to their possessor as to forbid the supposition that they were designed by a benevolent Creator. Only here and there a link out of the long chain of evidence can be given in a statement so condensed as the present one must be made. But it is evident, from the brief statement of facts embodied in the earlier part of the chapter, that, on the whole, the process of development of the embryo is what we should expect it to be if the theory