RUDIMENTARY ORGANS.

One of the strongest arguments in favor of the hypothesis of a genetic connection among all animals (including man), at least among all those belonging to the same great types, is the presence of rudimentary parts. By rudiments in anatomy are meant organs or structures imperfectly developed, so as to be almost or entirely without functional use. "Each of them represents in germ, as it were, in one animal (or plant), that which is perfect and useful in another type."

For a few examples: The little fold of caruncle at the inner margin of the eye in man, represents the nictitating membrane of birds. Eyes which do not see form a striking example. These are found in very many animals which live in the dark, as in caves or underground. Their eyes are often perfectly developed but are covered by a membrane, so that no ray of light can enter and they can never see. Such eyes, without the function of sight, are found in several species of moles and mice which live underground, in serpents and lizards, in amphibious animals (proteus, cæcilia) and in fishes; also in numerous invertebrate animals which pass their lives in the dark, as do many beetles, crabs, snails, worms, etc.

Other rudimentary organs are the wings of animals which cannot fly. For example, the wings of the running birds, like the ostrich, emeu, cassowary, etc., the legs of which become exceedingly developed. The muscles which move the ears of animals are still present in man, but of course are of no use; by continual practice persons have been able to move their ears by these muscles. The rudiment of the tail of animals which man possesses in his 3-5 tail vertebræ, is another rudimentary part—in the human embryo it stands out prominently during the first two months of its development; it afterwards becomes hidden. "The rudimentary little tail of man is irrefutable proof that he is descended from tailed ancestors." In woman the tail is generally, by one vertebra, longer than in man. There still exists rudimentary muscles in the human tail which formerly moved it.

Another case of human rudimentary organs, only belonging to the male, and which obtains in like manner in all mammals, is furnished by the mammary glands on the breast, which, as a rule, are active only in the female sex. However, cases of different mammals are known, especially of men, sheep and goats, in which the mammary glands were fully developed in the male sex, and yield milk as food for their offspring. The vermiform appendix of the large intestine in man, is another illustration of a part which has no use, but in one marsupial is three times the length of its body. The rudimentary covering of hair over certain portions of the body, is not without interest. Over the body we find but a scanty covering, which is thick only on the head, in the armpits, and on some other parts of the body. The short hairs on the greater part of the body are entirely useless, and are the last scanty remains of the hairy covering of our ape ancestors. Both on the upper and lower arm the hairs are directed toward the elbow, where they meet at an obtuse angle—this striking arrangement is only found in man and the anthropoid apes, the gorilla, chimpanzee, orang, and several species of gibbons. The fine short hairs on the body become developed into "thickset, long, and rather coarse dark hairs," when abnormally nourished near old-standing inflamed surfaces.[32] The fine wool-like hair or so-called lanugo with which the human fœtus, during the fifth and sixth months, is thickly covered, offers another proof that man is descended from an animal which was born hairy, and remained so during life. This covering is first developed during the fifth month, on the eyebrows and face, and especially around the mouth, where it is much longer than that on the head. Three or four cases have been recorded of persons born with their whole bodies and faces thickly covered with fine long hairs. Prof. Alex. Brandt compared the hair from the face of a man thus characterized, aged thirty-five, with the lanugo of a fœtus, and finds it quite similar in texture. Eschricht[33] has devoted great attention to this rudimentary covering, and has thrown much light on the subject. He showed that the female as well as the male fœtus possessed this hairy covering, showing that both are descended from progenitors, both sexes of whom were hairy. Eschricht also showed, as stated above, that the hair on the face of the fifth month fœtus is longer on the face than on the head, which indicates that our semi-human progenitors were not furnished with long tresses, which must therefore have been a late acquisition. The question naturally arises, is there any explanation for the loss of hair covering?

Fig. I.

Fig. I.—The Hairy-Faced Burmese Family. (From Scientific American, Feb. 20, 1875.)