File:The evolution of man- a popular exposition of the principal points of human ontogeny and phylogene (1896) (14778555801).jpg

Identifier: evolutionofmanpo02hae (find matches)
Title: The evolution of man: a popular exposition of the principal points of human ontogeny and phylogene
Year: 1896 (1890s)
Authors: Haeckel, Ernst, 1834-1919
Subjects: Evolution Embryology, Human Anatomy, Comparative Human beings
Publisher: New York, Fowle
Contributing Library: Smithsonian Institution Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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een the outer skin-furrow and the blind endof the intestine, and this disappears when the opening ismade.^^ Directly in front of the anus the allantois grows out ofthe posterior intestine; this is the important embryonicappendage which develops, in Placental Animals, and onlyin these (thus in Man too) into the placenta (Figs. 278, 279,1;Plate V. Fig. 14, al). In this more developed form—repte-sented in the diagi-am (Fig. 94, ^, vol. i. p. 812)—the intestinal 324 THE EVOLUTION OF MAN; canal of Man, like that of all other Mammals, now forms aslightly-curved, cylindrical tube, which has an opening atboth ends, and from the lower wall of which depend twosacs; the anterior navel-bladder, or yelk-sac, and the pos-terior allantois, or primitive urinary sac. Microscopic observation shows that the thin wall of thissimple intestinal tube and of its two bladder-like append-ages is composed of two distinct cell-strata. The inner,which coats the entire cavity, consists of larger, darker cells.
Text Appearing After Image:
Fig. 278.—Hmnan embryo of the third week, with the anlnion andallantois. The great globular yelk-sac is below, the bladder-like allantoison the right; there are as yet no limbs. The germ, with its appendages, isenclosed in the tufted membrane (chorion). Fig. 279.—Human embryo, with amnion and allantois, in the fourthweek. (After Krause.) The amnion (w) lies pretty close to the body. Thegreater part of the yelk-sac (d) has been torn away. Behind this the allan-tois appears as a small pear-shaped bladder. Arms (/) and legs (b) arealready commenced: v, fore-brain; z, twixt-brain; m, mid-brain; h, hind-brain i n, after-brain; a, eye; Tc, three gill-arches; c, heart; s, tail. RUDIMENT OF THE INTESTINAL CANAL. 325 and is the intestinal-glandular layer. The outer stratumconsists of lighter, smaller cells, and is the intestinal fibrous-layer. The cavities of the mouth and the anus are the onlyexceptions to this, because they originate from the outerskin. The inner cell-coating of the enti

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