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Excerpt from Journal of Experimental Zoology, 1928, Vol. 15 Boveri ('02, '05) found that the size of the nuclei of the cells of sea urchin larvae is directly proportional to 'the number of chromosomes-which enter them, and that cells which contain small nuclei are below the normal size, because such cells divide more frequently than those with large nuclei. In a number of publications, the earliest of which appeared in 1890, Minot advanced the view that differentiation, senescence and death are concomitant with, and the result of, an increase in the proportion of cytoplasm to nucleus in cells. Minot holds that the egg, at the earliest stage of its development, is actually in a senile state in which there is an excessive amount of cytoplasm as compared with the nucleus. During the process of cleavage, however, this relation is reversed by a rapid increase in the nuclear material. Thus rejuvenation is brought about chiefly by the segmentation of the egg, and depends upon the increase of the nucleus; and senescence gradually appears as development proceeds on account of the increase of the cytoplasm which is necessary for the differentiation of the cells. He wrote ('97, p. 370): The animal, when it is young, has cells with a small amount of protoplasm... In order that perfection of the adult structure should be attained, it is necessary that the mere undifferentiated cells, each with a small body of protoplasm, should acquire first an increased amount of protoplasm, and then from the increased protoplasm should be taken the material to result in differentiation, in specialization. The increase of the protoplasm is... the mark both of advancing organization and advancing age. In regard to the lower forms Minot says: If it be true that there is among Protozoa, among unicellular animals, anything comparable to the gradual decline in the growth power which occurs in us we shall expect it to be revealed in the condition of t