THE AGE OF FEMALE BLUE WHALES 233 



which were carefully kept by Mr R. Squire on board the 'Southern Empress'. The 



latter showed: Male 102 or 53-6% 



Female 88 or 46-4% 



The tendency for males to predominate is further confirmed by the general statistics for 

 the season 1933-4, shown on pp. 22-30 of International Whaling Statistics, vol. vi (1935). 

 1540 Blue whale foetuses are recorded of which 537 per cent were males and 46-3 per 

 cent females. 



foetal growth curve. Fig. 3 shows the disposition of length in foetuses measured 

 during the season 1932-3 on board the ' Southern Princess ' and the ' Southern Empress '. 

 The mean monthly lengths are shown. The freehand curve is a transcription of the mean 

 growth curve shown by Mackintosh and Wheeler (p. 423). Monthly averages from the 

 same source are shown also. The pelagic averages afford a striking confirmation of the 

 South Georgia growth curve. As a result of the much greater number of observations, 

 the monthly average lengths actually approach the mean curve more closely than do the 

 South Georgia monthly averages (except for February, when only five measurements 

 were taken on board the ' Southern Princess'). July may be fixed as the probable mean 

 date of pairing of whales taken in pelagic whaling as of those taken in South Georgia. 

 The similarity in breeding habit here shown is good evidence that the general way of 

 living of South Georgia and pelagic Blue whales is much the same, that they pair at the 

 same mean time of year, if not on the same grounds, and that the rate of foetal growth 

 is identical. 



ovaries: corpora lutea. 180 pairs of ovaries were examined on board the ' Southern 

 Princess ' and a record was made of the numbers of corpora lutea and corpora albicantia. 

 It was hoped that with the wealth of material at the investigator's disposal in pelagic 

 whaling it might be possible to work out a scheme of age definition of Blue females from 

 the distribution of numbers of corpora lutea, in the same way as was applied to Fin 

 whales. Wheeler (1930) showed that with Fin whales a correlation could be made between 

 the numbers of corpora lutea in the ovaries and the approximate age of the whale. The 

 basis of the correlation was that certain numbers of corpora lutea were found to be more 

 common than others. The intervals between these numbers indicate the mean number 

 of ovulations, fertilized or unfertilized, between one breeding cycle and the next. Hence 

 it was possible to calculate the approximate age of Fin females from the record of ovula- 

 tions in the ovaries. Wheeler went further and correlated the attainment of physical 

 maturity with the numbers of corpora lutea and hence with the age of the whale. 



The present writer attempted to apply the same methods to Blue whales, but no 

 regular occurrence of common numbers was observed. A frequency graph of corpora 

 lutea numbers appears in Fig. 4 together with frequencies derived from examination of 

 the large collections made in 1934-5 and 1935-6. These latter will be treated in more 

 detail later. For the moment it will suffice to point out that in these three sets of 

 frequencies peaks do not occur at regular intervals, nor do they occur at the same 

 numbers of corpora lutea in the different years. Owing to this lack of agreement with 



