THE HUMPBACK WHALE 



53 



corpus luteum b. While young and functional it is classified as a corpus luteum a but 

 when older and degenerating as a corpus luteum b. The transition is obviously gradual 

 with no sharp dividing line between the stages. Old corpora lutea b are, strictly, corpora 

 albicantia. There are thus two kinds of corpus luteum b, unfortunately undistinguishable, 

 but of very distinct origin, those representing a former pregnancy and those representing 

 ovulation not followed by pregnancy. The differences between corpora lutea a and b 

 are fully described by Mackintosh and Wheeler (1929). 



Fig. 50, which may be compared with the similar figures for Fin and Blue whales 



l'5 



Length of Foetus in metres 



o 

 © 



Corpus luTeum of preg'nancq 

 Largest co-existing corpus lufeurn 

 Corpus luteum of ovuldtion 

 • Corpus luteum of lactation 



Fig. 50. Humpback whale. Females. Size of corpora lutea. 

 The points to the right of the vertical line represent values obtained from non-pregnant whales. 



given by Mackintosh and Wheeler (1929), shows the size of corpora lutea a and b plotted 

 against the length of the foetus. Observations are only available from early stages of 

 pregnancy, but the fact emerges that in the Humpback the corpora lutea, both those of 

 ovulation and pregnancy (corpora lutea a) and those persisting during lactation and 

 during later pregnancies (corpora lutea b) tend to be distinctly larger than in the Fin 

 whale, being intermediate in size between those of the Fin and Blue whales. This is 

 rather unexpected considering how much greater is the size of those species than that 

 of the Humpback, and that the ovaries of the latter are smaller. 



Uterus. The routine measurement of the width of the uterine cornua was taken in 

 some of the female Humpbacks examined. It is to be regretted that this measurement 



