12 



DISCOVERY REPORTS 



the two places; the differences in the figures, where not due to inadequate numbers, are 

 to be explained by the higher proportion of immature whales in the South African 



catches. 



A summary of the analysis of the figures is shown in Table IV, in which the measure- 

 ments, expressed as percentages of the total length, are given separately for males and 

 females from South Georgia, from South Africa, and as totals. The number of measure- 

 ments producing each mean value is also shown. 



Table IV. Humpback whale. Mean value of measurements of male ayid female whales, 



expressed as percentages of the total length 



The only measurement that differs widely in the two sexes is no. 13, centre of anus to 

 centre of reproductive aperture ; it is nearly two and a half times greater in males than 

 in females. This is due to the penis being more anterior in position than the vulva. 

 In addition smaller differences are indicated in the relative lengths of the head and 

 flipper, both of which are slightly longer in the female than in the male. These dif- 

 ferences in relative length are probably due to the fact that the female Humpback 

 reaches a greater total length than the male of corresponding age, and thus depend on 



