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And still others flew like bats or birds. They were terrible forms, with coats of mail and powerful jaws and teeth. And they were active and swift. When we look at them we see that the vertebrate, though slow in gaining the lead, is sure to hold it. The internal skeleton gave fewer advantages at the start; its greatest superiority had lain in future possibilities.
In the vertebrate series, the least intelligent members, namely fishes and amphibians, do not possess complex instincts; and among mammals the animal most remarkable for its instincts, namely the beaver, is highly intelligent, as will be admitted by every one who has read Mr. Morgan's excellent work.
Thus the chief advantage in organisation by which the earliest Vertebrates took precedence of the unsegmented Chordonia consisted in the development of internal segmentation. The whole vertebrate stem divides first into the two chief sections of Acrania and Craniota. The Craniota descend directly from the Acrania, and these from the primitive Chordonia.
The vertebrate impulse began in wormlike forms, in the old Palaeozoic seas, and stopped not till it culminated in man. This impulse has left many forms behind it; but has this impulse itself ever been endangered? If one looks at the matter thus in an abstract instead of a concrete way, the problem of our descent becomes easier.
In 1816 the famous Ossements Fossiles, describing these novel objects, was published, and vertebrate paleontology became a science.
If it arose from an aquatic organ, like the wing of the penguin, we have then a singular divergence from the ordinary vertebrate fin-limb.
His absorption in his studies was intense as at one time he signs himself to his fellow-worker, W. K. Parker, "Ever yours amphibially," so Jeffery Parker, his demonstrator, who tells the story, came to him with a question about the brain of the codfish at a time when he was deep in the investigation of some invertebrate group. "Codfish?" he replied; "that's a vertebrate, isn't it?
He had also propounded the theory that "the development of the human body might possibly be traced from the radiated vermicular molluscous and vertebrate organisms," thirty years before Darwin published The Origin of Species.
But it was necessary to show the descent of the vertebrates from the lower forms. In order to respond to such a necessity, men sometimes reverse their conclusions. Although favorably disposed to the doctrine of the transmutation of the animalic forms, I want a complete proof before I can believe in a transformation of the vertebrate type into that of the mollusca."
He walked to and fro from the College with little slips of mnemonics in his hand, lists of crayfish appendages, rabbits' skull-bones, and vertebrate nerves, for example, and became a positive nuisance to foot passengers in the opposite direction. But, by a natural reaction, Poetry and the girl with the brown eyes ruled the Christmas holiday.
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