414 



DISCOVERY REPORTS 



of Others at eighteen and twenty-one. The whales can be grouped round each of these 

 peaks as follows : Group I, whales with one, two, three or four corpora lutea ; Group II, 

 whales with five to nine; Group III, with ten to fourteen; Group IV, with fifteen to 

 nineteen; Group V, with twenty to twenty-four. 



We have thus in the number of corpora lutea an indication of the age of any female 

 Fin whale up to eight years from sexual maturity ; and because each group is composed 

 mainly of pregnant and lactating whales or of resting whales one year older, we can 

 obtain a rough idea of the number of each age caught during the season from the 

 number of whales in each group as indicated by the frequency chart. 



NUMBER OF CORPORA LUTEA 



Fig. 3. Fin whales, females: Season 1929-30. Frequency of numbers of corpora lutea. 



Vertebral epiphyses not ankylosed throughout column. 



Vertebral epiphyses ankylosed throughout column. 



The assumption has here been made that pregnancy recurs every two years. That 

 this is in all probability normal behaviour is shown in the Report (1929, p. 431) from 

 consideration of the percentage of pregnant and resting whales. During 1929-30 

 pregnant, lactating and resting whales constituted 64, 17 and 12 per cent respectively 

 of the catch of mature females. The remaining 7 per cent were ovulating. The per- 

 centage of pregnant whales is rather high — theoretically it should be 50 per cent — 

 but allowing for possible segregation and seasonal variation the figures point to 

 a recurrent pregnancy at intervals of two years. 



In several resting whales the size and condition of the mammary glands showed that 

 lactation had not long ceased, and seven whales from a total of 199 were pregnant 



