Page:Popular Science Monthly Volume 71.djvu/368

362 they arose. There is thus, we learn, the constant fluctuation in the size of cells, a fluctuation in their dimensions accompanying the process of cell division. Presently we shall have more to say in regard to this matter of the change in the cell in size. The next picture (Fig. 40) which I want to recall to you is one which we also had in an earlier lecture. These represent slices through a very young rabbit before any of the organs of the rabbit have begun to develop. We can see here clearly the nuclei, as I pointed out to you before, nearly uniform in structure, and you notice that the protoplasm around each nucleus is quite small in amount. If you will recall the previous picture of the skin of the salamander, upon the screen a moment ago, you will realize immediately, in comparing the two, that in these young cells the proportion of the protoplasm to the nucleus is very small. That is again one of the fundamental facts to which we shall recur in a moment. I wanted to show you this picture in order to revive in your minds the conception which I endeavored to give you before of the undifferentiated tissue, where the cells have nuclei pretty