Discovery reports (1938) Discovery reports discoveryreports17inst Year: 1938 THE HUMPBACK WHALE 63 corpora lutea b. Some small follicles were visible in both ovaries. A foetus 0-51 m. long was present. The vagina was congested and vulva open, possibly owing to decomposition. The whale was not lactating and the mammary gland was 8 cm. thick and involuted. The whale had therefore been pregnant previously and the present pregnancy had probably been established at the first ovulation of the last sexual cycle. No. 2873. Length 13-05 m. 29. xii. 28. South Georgia. Lactating. One ovary weighed 9 oz
Discovery reports (1938) Discovery reports discoveryreports17inst Year: 1938 THE HUMPBACK WHALE 63 corpora lutea b. Some small follicles were visible in both ovaries. A foetus 0-51 m. long was present. The vagina was congested and vulva open, possibly owing to decomposition. The whale was not lactating and the mammary gland was 8 cm. thick and involuted. The whale had therefore been pregnant previously and the present pregnancy had probably been established at the first ovulation of the last sexual cycle. No. 2873. Length 13-05 m. 29. xii. 28. South Georgia. Lactating. One ovary weighed 9 oz. and contained one corpus luteum b of mean diameter 5-5 cm. Some follicles 5 mm. in diameter were present below the surface. The other ovary weighed seven ounces and contained no corpora lutea. The uterine cornu on the side of the ovary with the corpus luteum was 20 cm. across and the other one 22-5 cm. This whale was lactating, the mammary gland being 15 cm. thick and milk spouting from the nipples when the whale was drawn up on the flensing plan. An anterior tag, representing the remains of the vaginal band, was present. This whale was, therefore, nursing her first calf and pregnancy had taken place at the first ovulation of the first sexual season. Of these whales, nine are multipara, three pregnant or lactating for the first time, and five uncertain. At South Georgia for December there are three whales, one lactating, one in very early pregnancy and one in slightly later pregnancy. For January there are ten whales, seven in early pregnancy and three resting. For February there are three whales all in early pregnancy. For March there are two whales, one ovulating, the other lactating. At Durban, South Africa, there is one whale in anoestrus in June. The cause of the prolongation of the breeding season mentioned above is no doubt the fact that this species, like other whales, is polyoestrous and that females frequently do not become pregnant at the first ovulation of the sex
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