138 



DISCOVERY REPORTS 



monthly intervals on each side of it, the points are divided up into a number of groups 

 representing pregnancies starting in each month. When the pregnancies are counted 

 and plotted against months, the curve shown in Fig. 42 giving the frequencies of 

 pairing by months, is obtained. This makes it clear that the majority of pairings take 

 place in the months of August to December inclusive, with the maximum in October. 

 By plotting the same curve with the time scale shifted 15 months later the curve of 

 birth frequencies shown in Fig. 43 is obtained. This shows the season of parturition 

 extending from December to April, with the maximum in February. 



'jun'jul'Aug'Sep Oct Nov Dec Jan Feb Mar Apr 



Fig. 42. Sperm whale. Pairing frequencies by months. 



Oct Nov Dec Jan Feb Mar Apr Maij Jun Jul Aug 



Fig. 43. Sperm whale. Birth frequencies by months. 



The length of the foetus at birth is about 4 m. or a little more: the largest foetus 

 recorded was 4-26 m. long and the length of a newly born calf (Wheeler, 1933) was 



4-04 m. 



Sexual cycle. Only fourteen female Sperm whales have been examined, and conse- 

 quently the data for these are given in detail before the events of the sexual cycle are 

 discussed on general lines. All were examined at South African stations. 



