| OCR Text |
Show 206 THE DESCENT OF 1\'IAN. : PART I. been derived. We should thus be justified in believing that at an extremely remote period a group of animals . existed, resembling in many respects the larvre of our present Ascidians, which diverged into two great branches-the one retrograding in development and producing the present class of Ascidians, the other rising to the crown and summit of the animal kingdom by giving birth to the Vertebrata. We have thus far endeavoured rudely to trace the genealogy of the Vertebrata by the aid of their mutual affinities. vVe will now look to man as he exists ; and we shall, I think, be able partially to restore during successive periods, but not in due order of time, the structure of our early progenitors. This can be effected by means of the rudiments which man still retains, by the characters which occasionally make their appearance in him through reversion, and by the aid of the principles of morphology and embryology. The various facts, to which I shall here allude, have been given in the previous chapters. The early progenitors of man were no doubt once covered with hair, both sexes having beards; their ears were pointed and capable of movement; and their bodies were provided with a tail, having the proper muscles. Their limbs and bodies were also acted on by many muscles which now only occasionally reappear, but are normally present in the Quadrumana. The great artery and nerve of the humerus ran through a supra-condyloid foramen. At this or some earlier period, the intestine gave forth a much larger diverticulum or crecum than that now existing. The foot, judging from the condition of the great toe in the fretus, was then prehensile; and our progenitors, no doubt, were arboreal m their habits frequenting some warm. forest-clad and. The male~ CHAP. VI. AFFINITIES AND GENEALOGY. 207 were provided with great canine teeth, which served them as formidable weapons. At a much earlier period the uterus was double ; the excreta were voided through a cloaca ; and the eye was protected by a third eyelid or nictitating membrane. At a still earlier period the progenitors of man must have been aquatic in their habits; for morphology plainly tells us that our lungs consist of a modified swim-bladder, which once served as a float. The clefts on the neck in the embryo of man show where the branchire once existed. At about this period the true kidneys were replaced by the corpora wolffiana. The heart existed as a simple pulsating vessel; and the chorda dorsalis took the place of a vertebral column. These early predecessors of man, thus seen in the dim recesses of time, must have been as lowly organised as the lancelet or amphioxus, or even still more lowly organised. There is one other point deserving a fuller notice. It has long been known that in the vertebrate king- dom one sex bears rudiments of various accessory parts, appertaining to the reproductive system, which properly belong to the opposite sex; and it has now been ascertained that at a very early embryonic period both sexes possess true male and female glands. Hence some extremely remote progenitor of the whole vertebrate kingdom appears to have been hermaphrodite or androgynous.23 But here we encounter a singular 23 This is the conclusion of one of the highest authorities in comparati, ve anatomy, namely, Prof. Gegenbaur: 'Grundziige der vergleich. Anat. 1870, s. 876. The result has been arrived at chiefly from the study of the Amphibia; but it appears from the researches of Waldeyer (as q1:1oted in Humphry's 'Journal of Anat. and Phys.' 1869, p. 161), that the sexual organs of even ''the higher vertebrata are, in their early " condition, hermaphrodite." Similar views have long been held by some authors, though until recently not well based. I I . |
