Abstract
Hypophyses of 71 [male] ground squirrels (Citellus) were assayed at monthly intervals during 2 annual sexual cycles, using as recipient an immature [female] mouse (1 gland to 1 mouse). Gonadotropic potency was high with spermatozoa and extremely low during aspermia. Seasonal reduction of potency was prevented by castration of the squirrel or by subjection to continuous low temp. [male][male] show a slight potency at 2 mos. of age, low at 3-5, high preceding spermatozoa.