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He will be forced to admit that the close resemblance of the embryo of man to that, for instance, of a dog the construction of his skull, limbs and whole frame on the same plan with that of other mammals the occasional appearance of various structures, for instance, of several distinct muscles, which man does not normally possess, but which are common to the Quadrumana and a crowd of analogous facts all point in the plainest manner to the conclusion that man is the co-descendant of other mammals of a common progenitor.
Considering this parallelism, there can be little doubt that the same cause, whatever it may be, has acted on mammals and birds; and the result, as far as ornamental characters are concerned, may be attributed, as it appears to me, to the long-continued preference of the individuals of one sex for certain individuals of the opposite sex, combined with their success in leaving a larger number of offspring to inherit their superior attractions.
The progress of life is then described as the basis of subdivision into Geological Ages; and the subdivisions of geological time are presented as follows: I. Azoic Time or Age. II. Palaeozoic Time. 1. The Age of Mollusks, or Silurian. 2. The Age of Fishes, or Devonian. 3. The Age of Coal Plants, or Carboniferous. III. Mesozoic Time. 4. The Age of Reptiles. IV. Cenozoic Time. 5. The Age of Mammals.
We can hardly believe, however, that this would apply to white-colored butterflies, and this may be a reason why the effect of an insular habitat is more marked in these insects than in birds or mammals. But though inapplicable to the lower animals, this curious relation of sense acuteness with colors may have had some influence on the development of the higher human races.
"Gigantosteologie," at last the Professor burst out, between two words which I shall not record here. Then rushing on with renewed vigour, and with great animation: "Yes, gentlemen, I know all these things, and more. I know that Cuvier and Blumenbach have recognised in these bones nothing more remarkable than the bones of the mammoth and other mammals of the post-tertiary period.
Each of these is supplied with abundant nourishment, so that the young may develop to considerable size and activity before emerging from the egg. This material is enclosed in a firm protective shell and hidden away from sight by being buried in the ground. In the mammals comparatively few eggs are produced at one time.
Hence the Tertiary period may be called "the age of mammals." The highest section of this class, the placentals, now made their appearance; to this group the human race belongs.
Beside the lions, tigers, leopards, ounces, and other carnivorous mammals, amounting to eight hundred and ninety-two, there were in the ark six hundred and sixty-six eagles, for there are forty-eight species; one hundred and forty-four buzzards, fourteen hundred and forty-two falcons, one hundred and forty hawks, two hundred and thirty-eight vultures, and eight hundred and ninety six owls.
The reason he resembles a normal male in many respects is simply that sexuality in such highly-organized mammals is of the whole body, not of the sex-glands or organs alone. Suppose this horse was desexed at two years old. Nearly three years had elapsed since he was a fertilized egg. During the eleven months or so he spent within his mother, he developed a very complicated body.
But it is only when we come to air-breathing creatures that we find the vital characteristic of self-mobility manifested in the highest degree. Flying insects, mammals, birds, travel with velocities far exceeding those attained by any of the lower classes of animals; and so are more strongly contrasted with their inert environments.
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