. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. Fig. 14. Sections of the testis of the stickleback (Gasterosteus pungitius). (Modified from Moore, '39, after Van Oordt.) Cf. fig. 13. (A) Spermatogenic activity with many formed sperm in seminiferous tubules before the mating season, interstitial tissue in abeyance. (B) At mating period. Interstitial tissue well developed, spermatozoa stored in the tubules with spermatogenic activity -^:^\^^^^^f^^^^v^'^^^.^^k^^v^^^^^^^^j APRIL MAY JUNE J
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. Fig. 14. Sections of the testis of the stickleback (Gasterosteus pungitius). (Modified from Moore, '39, after Van Oordt.) Cf. fig. 13. (A) Spermatogenic activity with many formed sperm in seminiferous tubules before the mating season, interstitial tissue in abeyance. (B) At mating period. Interstitial tissue well developed, spermatozoa stored in the tubules with spermatogenic activity -^:^\^^^^^f^^^^v^'^^^.^^k^^v^^^^^^^^j APRIL MAY JUNE JULY AUG SEPT. OCT. Fig. 15. Seasonal reproductive cycle in the stickleback (Gasterosteus aculeatus). Cf. fig. 14. Breeding season is indicated by crosshatching below base line. Observe that spermatogenic activity follows rise of temperature, whereas interstitial-tissue and sex- character development occur during ascending period of light. (Redrawn from Turner; General Endocrinology, Philadelphia, Saunders, modified from Craig-Bennett, 1931.) c. Testicular Control of Body Structure and Function by the Male Sex Hormone 1) Sources of the Male Sex Hormone. Testosterone is prepared from tes- ticular extracts. It is the most potent of the androgens and is believed to be the hormone produced by the testis. The chemical formula of testosterone is: OH CHa ^\. 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 Nelsen, Olin E. (Olin Everett), b. 1898. New York, Blakiston
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