346 



DISCOVERY REPORTS 



Table 2. Immature fin whale females approaching puberty : mean maximum 



follicle diameters 



Mean max. follicle size (mm.) 



70 



60 



50 



a 40 



O 30 



y 20 



10 



IMMATURE 



NON-PREGNANT 



PREGNANT 



4 S 6 



DIAMETER IN CMS. 



10 



Text-fig. 2. Frequency distributions of maximum follicle diameters. 



that these were maturing follicles, but they may have reached a stage of development at which regres- 

 sion was about to begin. 



Mackintosh and Wheeler (1929) showed that the size of the largest follicle in female fin whales 

 approaching puberty increased from a minimum in January-April, to about 3 cm. in June and July. 

 There are in the present material 62 pairs of ovaries from immature females which were approaching 

 puberty (defined as females over 63 ft. in length, except for four immature females taken at Durban 

 which were 61-63 ft. in length). In Text-fig. 3 the means and variation of seven samples from January, 

 February, March, April and May combined, June and July combined, August, October and November 

 combined, are presented. The June/July sample is from Saldanha Bay, South Africa, and the August 

 sample is from Durban, South Africa. Although the size of the critical samples is small, this evidence 

 suggests that there is a follicular cycle showing one or more peaks from June to November or December, 

 when the maximum follicle size is about 3 cm. or more, and minimum values between December (or 

 January) and May, when the maximum follicle size is about 1 cm. or less. The absolute maximum 

 size, from an immature female taken in November, was about 5 cm. 



This agrees with conclusions about immature humpback whales based on material collected in the 

 breeding season of this species. Chittleborough (1954) states that immature females with follicles at 



