Page:Popular Science Monthly Volume 71.djvu/382

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POPULAR SCIENCE MONTHLY

ever-increasing number of cells which, in the last. of the figures upon the screen, have become so numerous that we are no longer able to readily count them. Every one of these cells has its own nucleus. When the process of segmentation is complete and reaches its final limit, we then see, if we examine that stage of development, cells of the young type, such as I have described to you, in which there is a nucleus with a small amount of protoplasm about each nucleus. It seems to me, therefore—and this is a new interpretation which I present

PSM V71 D382 Ambystomum punctatum progressive segmentation of the ovum.png

Fig. 50. Amblystomum punctatum. Progressive Segmentation of the Ovum. 1, unsegmented ovum; 9, advanced segmentation.

to you—that the process of segmentation of the ovum, with which the development of all the animals of the higher type invariably begins, is really the process of producing young cells. It is the process of rejuvenation. There is not any considerable growth of the living protoplasmic material of these eggs, and at the final stage the total volume of the egg is scarcely bigger than before; and such increased volume as has occurred has been due to the absorption of some of the surrounding water. In many animals not even this increase by the absorption