Verwandte Artikel zu Localized Stages in Development in Plants and Animals
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899. Excerpt: ... over, by taking the distal spines on these 23 rows, there result the same stages of spine development as shown in the longitudinal series along any primitive plication (Fig. 13). For example, in Spondylus, Figs. 12 and 13, two radial spinose plications, 1, 1, originate near the umbo. During growth the continuations of these plications diverge, and the Spondylus sp. 2. Sector showing diagrammatically the multiplication of radiating lines hy interpolation. The first zone A, has 2 radii; the second zone B, has 5 radii; the third zone C, has 11 radii; and the fourth zone D, has 23 radii. 13. Profiles of spines produced on the various radii at the four zones, as indicated in Fig. 12. A, the spines on the two primary radii of the first zone; B, the spines on the second zone, showing the growth of spines on the two primary radii (1, 1) and the small spines on the newly interpolated radii (2, 2, 2); C, the spines on the radii in the third zone; D, the spines at the bottom of the fourth zone. In zone 1) the two large compound spines (1,1) are on the two primary radii. Their development may be traced by following them through A, B, C, to D. The next longest spines (2, 2, 2) are tricuspid and represent the stage of spine development attained by the spines on the radii which were interpolated on the second zone B. The next smaller spines (3, 3, 3, 3, 3, 3) are on radii which were introduced in the third zone C. The twelve small spines (4, 4, etc.) are on the radii introduced on the fourth zone D. Thus, there are four stages of spine development shown on the lower margin of the fourth zone, and these correspond to the four stages seen in the series of spines on one of the primary radii running through the four zones. C. E. Beecher, Amer. journ. sci., 1898. spines beco...
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