6o 



DISCOVERY REPORTS 



which have crossed the equator and joined those of the southern hemisphere, and are 

 consequently in a stage of pregnancy different from that of the majority of their com- 

 panions. This possibiUty has been mentioned above and is discussed further in a later 



Jan Feb Mar Apr MaLj|Jun|Jul [Aug'ISep Oct|Nov| Dec 



Fig. 55. Humpback whale. Pairing frequencies by months. 



Jan Feb Mar Apr Maij Jun Jul Aug Sep Oct|Nov|Dec 



Fig. 56. Humpback whale. Birth frequencies by months. 



section. A further possibility to be noted is that some of the small amount of breeding 

 outside the main season may be due to renewed breeding by cows that have lost their 

 calves. 



Sexual cycle. The results of the examination of nineteen female Humpback whales are 

 now given, before considering the course of the sexual cycle. The whales are arranged 

 according to the dates of their capture. 



No. 317. Length 14-1 m. 9.1.26. South Georgia. Pregnant. This whale was very rotten, but was 

 pregnant with a foetus o-68 m. in length, and one ovary contained a corpus luteum a, 6-6 cm. in 

 mean diameter. 



No. 321. Length 14-9 m. 10. i. 26. South Georgia. Pregnant. Foetus, female 0-64 m. long. 

 The ovary containing the corpus luteum a (not measured) had no other corpora lutea and no scars. 

 The other ovary contained one corpus luteum b, 5-3 cm. in mean diameter, and was scarred. This 

 whale had therefore probably become pregnant at the second ovulation of the previous sexual cycle. 



