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 sexual cycle, and may experience 

 several dioestrous cycles before pregnancy occurs. The polyoestrous nature of the cycle 

 is shown by whale no. 3569 which was pregnant for the first time, as shown by the non- 

 parous condition of the mammary gland, but had more than one corpus luteum in the 

 ovary. Fig. 57 is a scatter diagram of the number of corpora lutea in the ovaries plotted 



Total Length in metres 



Fig. 57. Humpback whale. Females. Number of corpora lutea in the ovaries. 



