. Readings in evolution, genetics, and eugenics. Evolution; Heredity; Eugenics. THE BEARERS OF THE HERITAGE 299 Maturation of the sperm-cell.—In the maturation of the male gamete the germ-cell, now known as a spermatogonium, increases greatly in size to become a primary spermatocyte. In each primary spermatocyte the pairing of the chromosomes already alluded to occurs as indicated in Fig. 47, where six is taken arbitrarily to indicate the ordinary or diploid number of chromosomes, and three the reduced or haploid number. The division of the primary spermatocyte gives rise to two secondary sper
. Readings in evolution, genetics, and eugenics. Evolution; Heredity; Eugenics. THE BEARERS OF THE HERITAGE 299 Maturation of the sperm-cell.—In the maturation of the male gamete the germ-cell, now known as a spermatogonium, increases greatly in size to become a primary spermatocyte. In each primary spermatocyte the pairing of the chromosomes already alluded to occurs as indicated in Fig. 47, where six is taken arbitrarily to indicate the ordinary or diploid number of chromosomes, and three the reduced or haploid number. The division of the primary spermatocyte gives rise to two secondary spermatocytes (c), the paired chromosomes separating in such a way that a member of each pair goes to each. Fig. 48.—Diagram to illustrate oogenesis, a, showing the diploid number of chromosomes (six is arbitrarily chosen) as they occur in ordinary cells and in oogonia; b, the pairing of corresponding mates preparatory to reduction; c, d, the reduction division, giving off the first polar body; e, egg preparing to give off the second polar body, first polar body ready for division; /, second polar body ready for division; g, second polar body given off, division of first polar body completed. The egg nucleus, now known as the female pronucleus, and each polar body contain the reduced or haploid number of chromosomes. {From Guyer.) secondary spermatocyte. Each secondary spermatocyte (d) soon divides again into two spermatids (e), but in this second division the chromosomes each spht lengthwise as in an ordinary division so that there is no further reduction. In some forms the reduction division occurs in the secondary spermatocytes instead of the primary. Each spermatid transforms into a mature spermatozoon (/). The sper- matozoa of most animals are of linear form, each with a head, a middle-piece and a long vibratile tail which is used for locomotion. The head consists for the most part of the transformed nucleus and is consequently the part which bears the Please
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