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The first pulsations of the foetal heart must simultaneously aid the unfolding of every part. The growth of each tissue, by taking from the blood special proportions of elements, must modify the constitution of the blood; and so must modify the nutrition of all the other tissues.
There is no real coalescence of the two placentas at any part of the surface of contact. Hence at birth the foetal placenta alone comes away; the uterine placenta is not torn away with it. The formation of the placenta is very different in the second and higher section of the Placentals, the Deciduata. Here again the whole surface of the chorion is thickly covered with the villi in the beginning.
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 foetal whale are merely remnants recollections, if we may so say of the extinct whale.
All the evidence attainable goes to show, that the law of development is as immutable before as after birth, the several stages of progress succeeding each other in a constant order, and affecting the individual only, not the race. A young monkey is no more likely to be transmuted into a man than an old one; nor is such a metamorphosis at all more probable in the course of its foetal life.
For while the body floats in the mother's foetal fluid it is virtually exempt from the influence of the earth's field of gravity. History has given us a source of information from these early periods of man's existence in Traherne's recollections of the time when his soul was still in the state of cosmic consciousness.
To avoid this difficulty, he is driven to a further supposition, still more gratuitous and improbable; namely, that the germ destined to become one of a different race from its parents, having advanced along its usual line of development so far as that line coincides with the one belonging to the new species, there diverges, and follows a different path up to the period of its birth into a new creature; that is, the embryo of a reptile, having grown for a certain time as if it were to be a reptile, suddenly turns aside, like a young man changing his mind about the choice of a profession, and for the rest of its foetal life follows the proper line of progress in order to be developed into a bird.
Insanity has become an inflammation of the cortical substance of the brain: idiocy results from a foetal meningitis: genius is a form of scrofula closely allied to mania: in sleep, the brain loses blood, in intellectual excitement, attracts blood; in the illumination of the death-bed, or the delirium of drunkenness, the circulation through the brain is quickened; in torpidity, melancholy, stupidity, the circulation slackens and stagnates.
It certainly is a hard proposition, and it puts one upon his mettle to accept it. Should we not find equal difficulty in believing the life-history of each one of us, the start in the germ, then the vague suggestion of fish, and frog, and reptile, in our foetal life, were it not a matter of daily experience?
The tests which afford conclusive evidence of the existence of a foetus in the uterus are Ballottement, the uterine souffle, intermittent uterine contractions, foetal movements, and, above all, the pulsation of the foetal heart. The uterine souffle is synchronous with the maternal pulse; the foetal heart is not, being about 120 beats per minute.
And yet, at the outset of his studies, he finds that no adaptive reason whatsoever can be given for one-half of the peculiarities of vegetable structure; he also discovers rudimentary teeth, which are never used, in the gums of the young calf and in those of the foetal whale; insects which never bite have rudimental jaws, and others which never fly have rudimental wings; naturally blind creatures have rudimental eyes; and the halt have rudimentary limbs.
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