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When we try to construct an animal frame of the simplest conceivable type, that has some such primitive alimentary canal and the two primary layers constituting its wall, we inevitably come to the very remarkable embryonic form of the gastrula, which we have found with extraordinary persistence throughout the whole range of animals, with the exception of the unicellulars in the Sponges, Cnidaria, Platodes, Vermalia, Molluscs, Articulates, Echinoderms, Tunicates, and Vertebrates.
The general interest in Corals has called attention to the Polyps, and the accessible haunts of the Sea-Urchins and Star-Fishes have made the Echinoderms almost as familiar to the ordinary observer as the common sea-shells, while the Acalephs are usually to be found at a greater distance from the shore, and are not easily kept in confinement.
Gwyn Jeffreys, and others, have shown that on the same white mud there sometimes flourish Mollusca, Crustacea, and Echinoderms, besides abundance of siliceous sponges, forming, on the whole, a marine fauna bearing a striking resemblance in its general character to that of the ancient chalk.
And just as the most thorough acquaintance with physics, or chemistry, or general physiology, will not enable you at once to establish the balance of life in your private vivarium, so that your particular society of zoophytes, mollusks, and echinoderms may feel themselves, as the Germans say, at ease in their skin; so the most complete equipment of theory will not enable a statesman or a political and social reformer to adjust his measures wisely, in the absence of a special acquaintance with the section of society for which he legislates, with the peculiar characteristics of the nation, the province, the class whose well-being he has to consult.
It is all very fine to recognise in the ascending series of protozoa, cœlenterata, echinoderms, worms, mollusks, fishes, amphibia, reptiles, the stages of progress toward birds and finally to mammals and man. But whence comes the idea of bird or pigeon?
But this breast-plate, behind which the animal took shelter, constrained it in its movements and sometimes fixed it in one place. If the vegetable renounced consciousness in wrapping itself in a cellulose membrane, the animal that shut itself up in a citadel or in armor condemned itself to a partial slumber. In this torpor the echinoderms and even the molluscs live to-day.
No more ice, not much of echinoderms, plenty of fish, recall of ambassadors in partibus, and great severity toward booksellers, an infernal race, two or three of which have been killed under me." The ambassadors in partibus were the artists Agassiz employed and sent to England or elsewhere to draw fossil fishes for him in various museums, at a cost which Humboldt knew would be embarrassing.
The starfish, the most familiar representative of the Echinoderms, seems very far removed from the kind of worm-like ancestor we have been imagining, but, fortunately, the very interesting story of the starfish is easily learned from the geological chronicle.
There is no certainly known extinct order of Protozoa; there is but one among the Coelenterata that of the rugose corals; there is none among the Mollusca; there are three, the Cystidea, Blastoidea, and Edrioasterida, among the Echinoderms; and two, the Trilobita and Eurypterida, among the Crustacea; making altogether five for the great sub-kingdom of Annulosa.
Among the fossil shells common to Madeira and Porto Santo, large cones, strombs, and cowries are conspicuous among the univalves, and Cardium, Spondylus, and Lithodomus among the lamellibranchiate bivalves, and among the Echinoderms the large Clypeaster called C. altus, an extinct European Miocene fossil. The largest list of fossils has been published by Mr.
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