THE SPERM WHALE 



141 



lactation had finished. It is therefore evident that ovulation takes place at or a little 

 before the end of lactation, and thus pregnancy starts again very shortly after the nursing 

 of the last calf is finished. Fig. 44 shows the number of corpora lutea in the ovaries 





o 



Q_ 



(_ 



o 

 u 



U- 



o 



L 

 OJ 



30 100 110 



Total Length in metres 



Fig. 44. Sperm whale. Females. Number of corpora lutea in ovaries plotted against total length. 



plotted against length of whale. It shows a small degree of correlation between these 

 values for the extremes of whale length, but little for intermediate lengths. There is also 

 some indication of horizontal grouping about the levels of 4, 8-5 and 12 corpora lutea. 

 This is shown more plainly in Table XI in which the frequencies of corpus luteum 

 number are tabulated. It must be remembered that all these whales, with one doubtful 

 exception, are at least in their second breeding season, so that a large series of whales 

 including individuals in their first breeding season would show a further group at 1-2 

 corpora lutea. The data, though few, point to the probability that the Sperm whale has 

 a dioestrous cycle of about four ovulations at each oestrus after the first. 



Table XI. Sperm whale. Frequency of numbers of corpora lutea 



The information gained from a careful examination of female Sperm whales by 

 members of the Discovery staff" points strongly to the conclusion that there is no long 

 period of anoestrus in this species, but that oestrus recurs immediately the calf is weaned. 

 The fact that the Sperm whale is polygamous and each band of females is attended by 



