. The cell in development and inheritance. Cells; Cells. 324 THEORIES OF INHERITANCE AND DEVELOPMENT cially the service of Loeb, Herbst, and Driesch to show how essential a part is played by the environment in the development of specific organic forms. The limits of this work will not admit of any adequate review of the vast array of known facts in this field, for which the reader is referred to the works especially of Herbst. I shall only consider one or two cases which may serve to bring out the g"eneral principle that they involve. Every living organism at every stage of its existence
. The cell in development and inheritance. Cells; Cells. 324 THEORIES OF INHERITANCE AND DEVELOPMENT cially the service of Loeb, Herbst, and Driesch to show how essential a part is played by the environment in the development of specific organic forms. The limits of this work will not admit of any adequate review of the vast array of known facts in this field, for which the reader is referred to the works especially of Herbst. I shall only consider one or two cases which may serve to bring out the g"eneral principle that they involve. Every living organism at every stage of its existence reacts to its environ- ment by physiological and morpho- logical changes. The developing embryo, like the adult, is a moving equilibrium — a product of the response of the inherited organization to the external stimuli working upon it. If these stimuli be altered, development is altered. This is beautifully shown by the experiments of Herbst and others on the development of sea- urchins. Pouchet and Chabry showed that if the embryos of these animals be made to develop in sea-water con- taining no lime-salts, the larva fails to develop not only its calcareous skele- ton, but also its ciliated arms, and a larva thus results that resembles in some particulars an entirely different specific form; namely, the Tornaria larva of Balanoglossns. This result is not due simply to the lack of neces- sary material; for Herbst showed that the same result is attained if a slight excess of potassium chloride be added to sea-water containing the nor- mal amount of lime (Fig. 141). In the latter case the specific metabolism of the protoplasm is altered by a particular chemical stimulus, and a new form results. The changes thus caused by slight chemical alterations in the water may be still more profound. Herbst ('92) observed, for ex- ample, that when the water contains a very small percentage of lithium chloride, the blastula of sea-urchins fails to invaginate to form a typical gastrula, but
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectcells, bookyear1896
