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Updated: September 4, 2024
I am talking about that organ, the central organ of the vascular system of animals, a hollow muscular structure that propels the blood by alternate contractions and dilatations, which in the mammalian embryo first appears as two tubes lying under the head and immediately behind the first visceral arches, but gradually moves back and becomes lodged in the thorax." "Oh, do stop!
I presume that the object of gaining long periods of time instead of days in reading the Mosaic record, is to assume that the narrative means to describe the actual production on the earth of all that was created; in other words, to assume a particular meaning for the words "created," "brought forth," &c and then to make out that if a whole age is granted, Science will allow us a sequence of a "plant age" a "fish and saurian age," a "bird age," and a "mammalian age"; that is, in general terms and neglecting minor forms of life.
We have already seen that intra-uterine development of the young was being carried ever farther by mammals, and we found one explanation of this in the fact that each mammalian egg represented a large amount of nutriment, and that the mammal had very little material to spare for reproduction.
Throughout the long lapse of the secondary ages, across the lias, the oolite, the wealden, and the chalk, we find the mammalian race slowly developing into opossums and kangaroos, such as still inhabit the isolated and antiquated continent of Australia.
The fact that this immense fauna of Miocene Arctogaea is now fully and richly represented only in India and in South Africa, while it is shrunk and depauperized in North Asia, Europe, and North America, becomes at once intelligible, if we suppose that India and South Africa had but a scanty mammalian population before the Miocene immigration, while the conditions were highly favourable to the new comers.
In the first stages of the Tertiary period, in the age when we begin to trace the evolution of the suck-giving animals above the lowly grade in which the kangaroos and opossums belong, we find the ancestors of our mammalian series all characterized by rather weakly organized limbs fitted, as were those of their remoter kindred the marsupials, for tree climbing rather than for moving over the surface of the ground.
We have such mammalian cases as the Free-Martin cattle, and some convincing evidence of intersexuality in the human species itself, which will be reviewed presently. The notion of more "developmental energy" or a higher metabolism in males is borne out in the human species.
And this is reasonable enough, when one comes to think of it, for they represent a very antique and early type, the first rough sketch of the mammalian idea, if I may so describe them, with wits unsharpened as yet by contact with the world in the fierce competition of the struggle for life as it displays itself on the crowded stage of the great continents.
At Cromer and eastward, with abundant lignite beds and mammalian remains, and with cones of the Scotch and spruce firs and wood. At Runton, north-west of Cromer, expanding into a thick freshwater deposit, with overlying marine strata, elsewhere consisting of alternating sands and clays, tranquilly deposited, some with marine, others with freshwater shells. 4.
Before considering further the question of the corpora lutea as organs of internal secretion, we may briefly refer to the origin and structure of these bodies and of other parts of the mammalian ovary.
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