The evolution of man : a popular exposition of the principal points of human ontogeny and phylogeny . esentery-plate) (Fig. 318, Trip, p. 408).At this very important point in the ccelom-wall, where theendoccelar (or visceral ccelom-epithelium) merges into theexoccelar (or parietal ccelom-epithelium), in the embryo ofMan and the other Skulled Animals a small aggregation ofcells becomes visible, at a very early period, and this, accord-ing to Waldeyer,196 we may call the germ-epithelium, or(corresponding with the other plate-shaped rudiments oforgans) the sexual plate (Fig. 316, g; Plate IV. Fig
The evolution of man : a popular exposition of the principal points of human ontogeny and phylogeny . esentery-plate) (Fig. 318, Trip, p. 408).At this very important point in the ccelom-wall, where theendoccelar (or visceral ccelom-epithelium) merges into theexoccelar (or parietal ccelom-epithelium), in the embryo ofMan and the other Skulled Animals a small aggregation ofcells becomes visible, at a very early period, and this, accord-ing to Waldeyer,196 we may call the germ-epithelium, or(corresponding with the other plate-shaped rudiments oforgans) the sexual plate (Fig. 316, g; Plate IV. Fig. 5,/c). Thecells of this germ-plate, or sexual plate (lamella sexualis) areessentially distinguished by their cylindrical form and bytheir chemical constitution from the other cells of theccelom; they are of quite different significance from the flatcells of the serous ccelom-epithelium which line the 400 THE EVOLUTION OF MAN. remainder of the body-cavity (cosloma). Of these latter—the true ccelom-cells—those which invest the intestinaltube and the mesentery ( endoccelar ) originate from the. Fig. 316.—Transverse section through the pelvic region and the hindlimbs of an embryo Chick in the fourth day of incubation, enlarged about40 times: h, horn-plate; w, medullary tube; n, canal of the medullarytube ; u, primitive kidneys ; x, notochord; e, hind limbs ; b, allantois canalin ventral wall; t, aorta; v, cardinal veins ; a, intestine; d, intestinal-glandular layer; /, intestinal-fibrous layer; g, germ-epithelium; r, dorsalmuscles; c, body-cavity, or Ccelom. (After Waldeyer.) intestinal-fibrous layer (in Fig. 5, Plate IV., coloured red);those which line the inner surface of the external Avail ofthe abdomen ( exocoelar ) are, on the contrary, the productof the skin-fibrous layer (coloured blue in Fig. 5, Plate IV.);but the sexual cells which make their appearance at theboundary line between the two forms of ccelom-cells, and DIFFERENTIATION OF THE SEXES. 4OI which insert the
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Keywords: ., book, bookcentury1800, bookdecade1870, booksubjectembryologyhuman
