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Updated: May 22, 2025
It is quite possible to believe that, had this intermarriage of the two schools continued to bear fruit, some vertebrate style might have resulted from the union, partaking of the nature of both parents; but the hope was of short duration.
But no one would hold that the influence of light has physically caused the formation of a nervous system, of a muscular system, of an osseous system, all things which are continuous with the apparatus of vision in vertebrate animals.
How are we going to cross this chasm lying between the sun's rays and the sea slime upon the one hand, and the articulate and the vertebrate upon the other? Darwin says, "Judging from the past, we may safely infer that not one living species will transmit its unaltered likeness to a distant futurity." Well, how is it with the past?
Most curious experiments they were, for in effect they consisted of the making of two or more living creatures out of one, in the case of beings so highly organized as the sea-urchins, the little fishlike vertebrate, amphioxus, and even the lower orders of true fishes.
The brain of all except the very lowest vertebrates consists of four portions: 1. The cerebrum, or cerebral lobes, or simply "forebrain," the seat of consciousness, thought, and will, and from which no nerves proceed. Whether the primitive vertebrate had any cerebrum is still uncertain. 2. The mid-brain, which sends nerves to the eyes, and in this respect reminds us of the brain of insects.
From egg to sponge is, comparatively speaking, but a step; it is a long march from the egg to the earthworm; and the vertebrate embryo makes a vast journey. But embryonic life is and must remain short. Hence in higher forms the ancestral stages will often be slurred over and very incompletely represented.
This is the stem of the Tunicates. One member of this group, the sea-squirt, very closely approaches the lowest vertebrate, the Amphioxus, in its essential internal structure and embryonic development.
"Well, I don't believe he told them just what we wanted; and, at any rate, I'm done with agents. Tomorrow I'm going entirely by advertisements." Mrs. March took the vertebrate with her to the Vienna Coffee-House, where they went to breakfast next morning. She made March buy her the Herald and the World, and she added to its spiny convolutions from them.
Goodsir long ago insisted upon the resemblance between Amphioxus and the Ascidians; but the notion of a genetic connection between the two, and especially the identification of the notochord of the Vertebrate with the axis of the caudal appendage of the larva of the Ascidian, is a novelty which, at first, takes one's breath away.
Yet we must hesitate before we accept, even on such evidence, so sweeping a conclusion, as that the globe, for ages after it was inhabited by all the great classes of invertebrata, remained wholly untenanted by vertebrate animals. 1818: Lower Oolite: Stonesfield. 1847: Upper Trias: Stuttgart. Art. 1854: Lower Eocene: Woolwich Beds. 1858: Chloritic Series, or Upper Greensand: Cambridge.
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