Seasonal Changes in the Gonads.

In Table V are shown the mean weights of the gonads of the owls for each month. It will be seen that the usual avian changes are shown, the ovaries and testes about February or March being completely regressed and about equal in weight. Up to August the testes remain about the same, while the ovaries increase slightly. Then comes a tremendous increase in size and weight to the maximum in October or November, followed by an equally sudden decrease. The limits of weight are 0.02 and 1.50 grms. in the case of the ovary, and 0.01 and 0.34 grms. in the case of the testes. By comparison with the graph of body weight it is seen that the spring increase in weight of the female accompanies the increase in the ovary. It is not caused directly by it since the ovary only weighs some three grammes, and the mean body weight of the female at this period is at least 30 grammes more than that of the male. The increase in size of the testes is not accompanied by increased body weight in the male, nor are the changes in body weight accompanying the moult reflected in changes in the gonads.

At its smallest, the ovary measures roughly 8.0 × 4.0 mm. The eggs in it vary in circumference in different birds, those in which they are less conspicuous being possibly young birds which have not yet bred. Nine ovaries were recorded with dark spots on them, which