. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. FACTORS INFLUENCING ACTIVITIES OF THE TESTIS 35 the scrotum results in a corresponding failure of the seminiferous tubules to produce sperm. In these instances the testis may appear shriveled and shrunken (fig. 18). However, such cryptorchid (ectopic) conditions in most cases retain the ability to produce the sex hormone at least to some degree. A question therefore arises relative to the factors which inhibit seminiferous tubule activity within t
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. FACTORS INFLUENCING ACTIVITIES OF THE TESTIS 35 the scrotum results in a corresponding failure of the seminiferous tubules to produce sperm. In these instances the testis may appear shriveled and shrunken (fig. 18). However, such cryptorchid (ectopic) conditions in most cases retain the ability to produce the sex hormone at least to some degree. A question therefore arises relative to the factors which inhibit seminiferous tubule activity within the cryptorchid testis. The failure of cryptorchid testes to produce viable sperm has been of interest for a long time. Observations have demonstrated that the more hidden. Fig. 18. Experimental unilateral cryptorchidism in adult rat. The animal's left testis was confined within the abdominal cavity for six months, whereas the right testis was permitted to reside in the normal scrotal position. Observe the shrunken condition of the cryptorchid member. (After Turner: General Endocrinology, Philadelphia, Saunders.) the testis (, the nearer the peritoneal cavity) the less likely are mature sperm to be formed. A testis, in the lower inguinal canal or upper scrotal area is more normal in sperm production than one located in the upper inguinal canal or inside the inguinal ring. Studies made upon peritoneal and scrotal temperatures of rats, rabbits, guinea pigs, etc., demonstrate a tem- perature in the scrotum several degrees lower than that which obtains in the abdomen. These observations suggest that the higher temperature of the non-scrotal areas is a definite factor in bringing about seminiferous tubule injury and failure to produce sperm. With this temperature factor in mind. Dr. Carl R. Moore (in Allen, Danforth, and Doisy, '39) and others performed experiments designed to test its validity as a controlling influence. They found that confinement alone of an adult guinea pig t
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