. The cell in development and inheritance. Cells; Cells. GENERAL OUTLINE i8r spermatogonia from which the spermatozoa are ultimately formed (Fig. 90). Like the oogonia, the spermatogonia continue for a time to divide with the usual (somatic) number of chromosomes ; four in Ascaris inegalocepJiala bivalens. Ceasing for a time to divide, they. Fig. 91.— 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, sliowing the full number (four) of chromosomes. C. Primary spermatocyte pr
. The cell in development and inheritance. Cells; Cells. GENERAL OUTLINE i8r spermatogonia from which the spermatozoa are ultimately formed (Fig. 90). Like the oogonia, the spermatogonia continue for a time to divide with the usual (somatic) number of chromosomes ; four in Ascaris inegalocepJiala bivalens. Ceasing for a time to divide, they. Fig. 91.— 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, sliowing the full number (four) of chromosomes. C. Primary spermatocyte preparing for division ; the chromatin forms two tetrads. D. E. F. First division to form two secondary spermatocytes each of which receives two dyads. G. H. Division of the two secondary spermatocytes to form four spermatids. Each of the latter receives two single chromosomes and a centrosome which persists in the middle-piece of the spermatozoon. now enlarge considerably to form spermatocytes, each of which is morphologically equivalent to an unripe ovarian ovum, or oocyte. Each spermatocyte finally divides twice in rapid succession, giving rise first to two daughter-spermatocytes and then to four spermatids, each of which is directly converted into a single spermatozoon. The. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wilson, Edmund B. (Edmund Beecher), 1856-1939. New York : The Macmillan company
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectcells, bookyear1896
