The cell in development and inheritance . cleus, each dyadis halved to form two single chromosomes which enter the respec-tive spermatids (ultimately spermatozoa). From each spermatocyte,therefore, arise four spermatozoa, and each sperm-nucleus receiveshalf the usual number of single chromosomes. The parallel with theegg-reduction is complete. These facts leave no doubt that the spermatocyte is the morpho-logical equivalent of the oocyte or immature ovarian Q,gg, and thatthe group of four spermatozoa to which it gives rise is equivalentto the ripe ^gg plus the three polar bodies. Hertwig was t
The cell in development and inheritance . cleus, each dyadis halved to form two single chromosomes which enter the respec-tive spermatids (ultimately spermatozoa). From each spermatocyte,therefore, arise four spermatozoa, and each sperm-nucleus receiveshalf the usual number of single chromosomes. The parallel with theegg-reduction is complete. These facts leave no doubt that the spermatocyte is the morpho-logical equivalent of the oocyte or immature ovarian Q,gg, and thatthe group of four spermatozoa to which it gives rise is equivalentto the ripe ^gg plus the three polar bodies. Hertwig was thus led tothe following beautifully clear and simple conclusion: The polarbodies are abortive eggs which are formed by a final process of R 242 REDUCTION OF THE CHROMOSOMES division from the egg-mother-cell (oocyte) in the same manner as thespermatozoa are formed from the sperm-mother-cell (spermatocyte).But while in the latter case the products of the division are all usedas functional spermatozoa, in the former case one of the products. Fig. 119.— Diagrams showing the essential facts of reduction in the male. The somatic num-ber of chromosomes is supposed to be four. A. B. Division of one of the spermatogonia, showing the full number (four) of Primary spermatocyte preparing for division; the chromatin forms two tetrads. D. E. F. Firstdivision to form two secondary spermatocytes each of which receives two dyads. G. H. Divisionof the two secondary spermatocytes to form four spermatids. Each of the latter receives twosingle chromosomes and a centrosome which passes into the middle-piece of the spermatozoon. of the egg-mother-cell becomes the o-gg, appropriating to itself theentire mass of the yolk at the cost of the others which persist inrudimentary form as the polar bodies. ^ 1 90, I, p. 126. GENERAL OUTLINE 243 3. Weisnianns Interpretatio7i of Reduction Up to this point the facts are clear and intelligible. Before com-ing to closer quarters with them it will
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