Differential Effect of Some Gonadotropic Substances on Development of Cyclical Sex Characters in the English Sparrow. ∗

The English Sparrow, like all other wild birds of the temperate zone, has a cyclical sexuality. During the breeding season in spring and early summer the sex glands are large and active; in July or August they undergo a rapid involution. In the males the testes shrink to approximately one-thousandth of their maximal size and the ovary of the females regresses to about the condition characteristic of immature birds 2 or 3 months old. Some of the secondary sex characters, especially bill color and gonadal ducts, follow this seasonal cycle. During the period of gonadal involution the bill of the male is as light as that of a castrate and the oviduct of the female is as thin and straight as that of an immature or an ovariotomized bird. On the other hand during the breeding season the male bill is jet black and the female oviduct is voluminous and convoluted. Keck 1 has shown that these secondary sex characters are directly controlled by the corresponding male and female sex hormones. It is evident, therefore, that the involuted gonads of fall sparrows release sex hormones either not at all or in subthreshold quantities.

In an attempt to determine the possible rôle played by the hypophysis in this seasonal sex cycle, gonadotropic substances were injected into sparrows in sexual inactivity. In the winter of 1932 a group of quiescent males was injected with extracts from pregnancy urine, prepared and standardized in rat units in our own laboratory. No response was obtained, even though the exorbitant dosage of 50 units was administered daily during the whole month to some of the birds (Table I).