Spermatogenesis is a complicated process dependent upon several factors.
Hormones affect development, male gonads subjected to estrogen form an ovotestis, whereas ovaries exposed to aromatase inhibitors form an atypical testis. Sertoli cell numbers are set early in spermiogenesis, possibly under the influence of follicle-stimulating hormone and thyroid hormone, and this may determine the number of genial cells that can be supported. Sertoli cells make a number of substances that affect testicular development and function, particularly anti-Mullerian hormone, which inhibits female oviduct formation from the Mullerian anlage, inhibits aromatase activity to stop estrogen production, and possibly stimulates androgen production by Leydig cells. Transmission electron microscopy micrographs of turkey testis are presented, and control of spermatogenesis by hormones and cytokines is discussed. Although information concerning paracrine and autocrine regulation of the avian testis by these substances is sparse, much can be learned from mammalian studies, in which putative roles of each of these substances have been established.