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Updated: May 15, 2025
As regards the remaining organs of the Amphioxus, we need only mention that the gonads or sexual glands are developed very late, immediately out of the inner cell-layer of the body-cavity. For the rest, the subsequent development into the adult Amphioxus of the larva we have followed is so simple that we need not go further into it here.
Now I traced some delicate nervous filament from the spinal column of the amphioxus to the cerebral hemisphere of the mammifer. Now I disclosed the ramifying canals in the vast system of circulation, mounting from the spongy network of the mollusk and the sluggish lymphatic of the reptile to the brilliant, bounding arteries of the double-hearted vertebrates.
His scientific jargon was as bewildering as his slang; and there were even moments in his discourse when Miss Anson ceased to distinguish between them; but the suspense with which he continued to gaze on her acted as a challenge to her scattered thoughts. "The amphioxus," she murmured, half-rising. "It's an animal, isn't it a fish? Yes, I think I remember."
If we now look back on all the remarkable features we have encountered in the structure and the embryonic development of the Amphioxus and the Ascidia, and compare them with the features of man's embryonic development which we have previously studied, it will be clear that I have not exaggerated the importance of these very interesting animals.
Judge for yourself; the latter derives the genesis of man from a group of plastides, from the jelly-like moneron; this moneron, through the ameoba, the ascidian, the brainless and heartless amphioxus, and so on, transmigrates in the eighth remove into the lamprey, is transformed, at last, into a vertebrate amniote, into a premammalian, into a marsupial animal.... The vampire, in its turn, belongs to the species of vertebrates.
Oldest vertebrates without jaws or pairs of limbs, single nose. : 13. Acrania II. More recent. : 13. Leptocardia. Amphioxus. Oldest vertebrates without jaws or pairs of limbs, single nose. : 14. Petromyzonta larvae. Oldest vertebrates without jaws or pairs of limbs, single nose. : 15. Cyclostoma II. More recent. : 15. Marsipobranchia. Petromyzonta. Silurian. : 16. Selachii. Primitive fishes.
While the Amphioxus is thus connected through the Cyclostoma with the fishes, and so with the series of the higher vertebrates, it is, on the other hand, very closely related to a lowly invertebrate marine animal, from which it seems to be entirely remote at first glance.
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 further development of the Ascidia in detail has no particular interest for us, and we will not go into it. The chief result that we obtain from its embryology is the complete agreement with that of the Amphioxus in the earliest and most important embryonic stages.
When we turn from the Tunicates to the closely-related Amphioxus we are astonished at first to find an apparent retrogression in the formation of the vascular system. A number of branchial vascular arches, which effect respiration and rise in the wall of the branchial gut from belly to back, absorb oxygen from the water and give off carbonic acid; they connect the ventral with the dorsal vessel.
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