VERTEBRATA

(Lat. vertebra, ‘joint’), Chord at a, the great phylum of animals Rom. characterized primarily by the presence B. of a jointed internal axis supporting the body. In some of the le specialized by forms, (e.g.) Tunicates and the Lancelet, this backbone or vertebral column is not developed, but in these its place is DEL, taken by a-supporting unjointed and painter; elastic rod—the notochord—which even in the higher forms precedes in develop be ment the backbone (hence the name Chord at a). Besides this important Bartolomfeature, Vertebrates po e a nerve of chord embedded in the dorsal portion is of the body (a contrast to the ventral nerve-chord of Invertebrates): and a verse series of openings leading from the forepart of the food canal to the exterior, trifling which sometimes become functional to gill-slits or may remain embryonic of Prior The number of described species of poets Vertebrates falls little short of 40,000, and these form two great groups. The Paris, highest group — Amniota — comprises of Mammals (including man), Birds, and cost Reptiles, in all of which the embryo is (1661 protected by a ‘water-jacket’ membrane, by the amnion, surrounding the embryo (chief and keeping it suspended in a liquid with medium. With the amnion is a ociated gar a second embryonic membrane—the allantois—the main function of which stand is respiratory. Such structures are Fishes and (for phidians, which are there together as Anamnia, hgh