Archive image from page 100 of Cytology, with special reference to. Cytology, with special reference to the metazoan nucleus cytologywithspec00agar_0 Year: 1920 Ill GERM-TRACK 35 Now in the normal monospermic egg all the daughter chromosomes of the zygote nucleus which pass into the one blastomere (designated by Boveri, 5) undergo diminution, and all that go into the other (P) undergo their next mitosis intact. Thus, if the inducement to diminution were furnished by the chromosomes themselves, we would have to suppose that every chromosome of the normal zygote nucleus divides at meta- phase
Archive image from page 100 of Cytology, with special reference to. Cytology, with special reference to the metazoan nucleus cytologywithspec00agar_0 Year: 1920 Ill GERM-TRACK 35 Now in the normal monospermic egg all the daughter chromosomes of the zygote nucleus which pass into the one blastomere (designated by Boveri, 5) undergo diminution, and all that go into the other (P) undergo their next mitosis intact. Thus, if the inducement to diminution were furnished by the chromosomes themselves, we would have to suppose that every chromosome of the normal zygote nucleus divides at meta- phase into two daughter chromosomes, one of which is predestined to undergo diminution and the other is not. If this were the case in the dispermic egg, it would follow that six of the daughter chromosomes E F C Fig. 40. Diagram illustrating the part played by the cytoplasm in determining the diminution of the chromatin in Ascaris megalocephala. (After Boveri, Festschr. f. Hertwis, 1910.) The shaded portion represents the 'vegetative' cytoplasm. In every case the chromosomes remain intact in the cells containing this substance, and undergo diminution in the cells which lack it. A, undivided egg; B, C, D, stages in the production of the 4-cell stage in the normal, monospermic egg; E, F, G, results of the first cleavage of dispermic eggs. According to the orientation of the spindles with regard to the egg axis, one of the three types shown is obtained. produced by the metaphase of the first cleavage mitosis were predestined to undergo diminution, while their six sister chromosomes were not. Moreover, it would often result from the unequal distribution of the daughter chromosomes among the four primary blastomeres, that the same nucleus would contain a mixture of chromosomes predestined for diminution and of those predestined to remain intact. As a matter of fact, neither of these expectations is realized. Diminution may take place in one, two or three of the four cells formed by the
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