. The doctrine of descent and Darwinism. Evolution. 214 THE DOCTRINE OF DESCENT. cular pleasure," says Wiirtenberger, " when, after div^ers careful comparative studies, I at last detected an inter- esting and simple conformity to law in the variations of the Ammonites. Namely, on the first appearance of a modification which subsequently attains essential import- ance in an entire group, it is only slightly indicated on a portion of the last convolution. Towards more recent deposits, this modification is more and more plainly shown, and then advances, following the spiral course of. F
. The doctrine of descent and Darwinism. Evolution. 214 THE DOCTRINE OF DESCENT. cular pleasure," says Wiirtenberger, " when, after div^ers careful comparative studies, I at last detected an inter- esting and simple conformity to law in the variations of the Ammonites. Namely, on the first appearance of a modification which subsequently attains essential import- ance in an entire group, it is only slightly indicated on a portion of the last convolution. Towards more recent deposits, this modification is more and more plainly shown, and then advances, following the spiral course of. Fig. 19. Ammoiiiles Huniphresianus. A form analogous to the Planulata. the shell ; that is to say, it gradually takes possession of the central turns also, as we trace the forms to higher strata. This reproduction in younger stages of life of modifications first occurring at a more advanced age, makes but slow progress, so that we see the older forms repeated with great persistency in the central turns. Frequently a modification of this sort has taken posses- sion of only a small part of the convolutions, when a new one already appears at the outside, and follows the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Schmidt, Dr. (Eduard Oskar), 1823-1886. New York, D. Appleton
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