. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. REPRODUCTION AND DEVELOPMENT 287 round mass of cells. Now if the alcohol is removed before the injury is fatal, new mouths equipped with tentacles appear at several points around the edge of the flattened mass. It is interpreted to mean that the depressant action of the alcohol has extinguished the relation of dominance and subordination that obtains between the apical or mouth region and the remainder, and that new dominant regions arise when this depression is removed. One of the most commo
. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. REPRODUCTION AND DEVELOPMENT 287 round mass of cells. Now if the alcohol is removed before the injury is fatal, new mouths equipped with tentacles appear at several points around the edge of the flattened mass. It is interpreted to mean that the depressant action of the alcohol has extinguished the relation of dominance and subordination that obtains between the apical or mouth region and the remainder, and that new dominant regions arise when this depression is removed. One of the most common human congenital defects is harelip. It results from the failure, or partial failure, to fuse on the part of INDUCED NEURAL TUBE. NORMAL NEURAL TUBE Fig. 193.—An early salamander embryo with a normal neural tube and one in- duced to form by a small portion of the lip of the blastopore of another embryo transplanted into the side region (After Spemann and Mangold.) the two processes that grow out. from the primordium of the lower jaw on either side. Normally these two maxillary processes meet at the mid-line and fuse to form the upper jaw, upper lip, and palate. Harelip has no significance whatever, except the incomplete fusion of these two processes; it is not possible to state exactly the cause of this growth deficiency. While much of the detail of the nature of the processes that regu- late normal form in the development of the individual, and of their upset by environmental conditions, is yet obscure, in a general way abnormalities can be accounted for in terms of abnormalities in. 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 Buchanan, James William, 1888-. New York, London, Harper & brothers
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