. The physiology of reproduction. Reproduction. SPERMATOGENESIS—INSEMINATION 171 certain of the other cells in the parietal layer of the seminiferous epithehum. In male animals which have a rutting season spermato- genesis occurs only at this time. At other seasons of the year the testes remain in a quiescent condition.^ The periodic activity of the testis is usually correlated with a great increase in the size of that organ (see pp. 24 and 61). Spermatogonium. Oogonium. Proliferation Growth period. Maturation period. • • * Fig. 45.—Scheme of spermatogenesis and oogenesis. (After Bove
. The physiology of reproduction. Reproduction. SPERMATOGENESIS—INSEMINATION 171 certain of the other cells in the parietal layer of the seminiferous epithehum. In male animals which have a rutting season spermato- genesis occurs only at this time. At other seasons of the year the testes remain in a quiescent condition.^ The periodic activity of the testis is usually correlated with a great increase in the size of that organ (see pp. 24 and 61). Spermatogonium. Oogonium. Proliferation Growth period. Maturation period. • • * Fig. 45.—Scheme of spermatogenesis and oogenesis. (After Boveri.) The changes which occur in spermatogenesis may be sum- marised as follows : (1) A spermatogonium divides into two, one product of division passing into the second layer of the seminal epithehum and becoming a, spermatocyte. (2) A ' In some animals the renewal of activity in the testes is associated with the descent of these organs from their position in the abdominal cavity through the inguinal canal and into a cutaneous fold. This is transformed into the scrotum, which lies behind the penis (except in Marsupials, where it is in front). In many Mammals the descent takes place at an early age and is permanent. In others (most Bodents, lusectivores, and bats) the testes are withdrawn into the abdominal cavity after the breeding season is over. This is effected by the cremaster 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 Marshall, F. H. A. (Francis Hugh Adam), 1878-1949; Cramer, William, 1878-1945; Lochhead, James. London, New York, Longmans, Green
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectreproduction, bookyea
