. The elements of experimental embryology. Embryology, Experimental; Embryology. 368 GRADIENT-FIELDS IN POST-EMBRYONIC LIFE rest of the body. It is of interest to note that during the reduction in size that accompanies starvation in these animals, the trend in change of proportions is reversed, the trunk becoming relatively more reduced in size than the head, so that the proportions of an animal of a given size are the same whether it has been growing larger or becoming smaller.^ Special cases of great interest resuhing from graded growth are those of the shells of Molluscs and Brachiopods. In
. The elements of experimental embryology. Embryology, Experimental; Embryology. 368 GRADIENT-FIELDS IN POST-EMBRYONIC LIFE rest of the body. It is of interest to note that during the reduction in size that accompanies starvation in these animals, the trend in change of proportions is reversed, the trunk becoming relatively more reduced in size than the head, so that the proportions of an animal of a given size are the same whether it has been growing larger or becoming smaller.^ Special cases of great interest resuhing from graded growth are those of the shells of Molluscs and Brachiopods. In these cases "35 CO C C " .2 <u o. 12 3 4 5 5 7 Segments of abdomen: distal —> Fig. 177 Growth-gradients in the abdomen of crabs. The abscissae represent growth- coefficients (differential growth-ratios) of hnear dimensions of abdominal segments relative to carapace length. The ordinates refer to the abdominal segments; 7, telson. Solid line, breadth of segments: ® Teltnessus, (S; x the same, ?; + Pinnotheres (pea-crab), ?. The dotted line refers to segment-length in Pinnotheres, ?. (From Huxley, Problems of Relative Growth, London, 1932.) growth takes place at a definite growing edge, and the new material laid down solidifies and takes no further part in growth. A similar type of growth is found in other hard structures such as the horns of mammals, teeth, etc. D'Arcy Thompson^ first pointed out that the form and size of the horns of two-horned rhinoceroses could only be understood on the assumption of a growth-gradient, decreasing posteriorly, in the head region, affecting the proliferation of epidermal structures. This is of some general interest, as it can only manifest itself where Abeloos, 1928. ^ Growth and Form, 1917, p. 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
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Keywords: ., bookcentury1900, bookcollectionbiodiversi, booksubjectembryology
