342 DISCOVERY REPORTS 



animals are presented in Text-fig. i . The records for immature females are not of course representative 

 of the whole class of immatures, for, owing to the operation of the minimum length regulations, they 

 include only those animals which are nearing sexual maturity. The intersection of the curves for 

 immature and non-pregnant mature ovaries is at 0-6 kg. and for immature and pregnant ovaries at 

 0-95 kg., but owing to the wide variation in ovary weight near puberty there is a considerable overlap. 

 Between immature and non-pregnant mature, the overlap is from 0-25 to 175 kg., and between 

 immature and pregnant from 075 to 175 kg. It is not, therefore, possible to distinguish between all 

 immature and mature females on the basis of ovary weight. The mean ovary weights for the different 

 classes are shown in Table 1 . The difference between the mean ovary weight of pregnant and non- 

 pregnant mature females is both absolutely and proportionately much greater than Chittleborough 

 (1954) noted for the humpback whale, and is statistically significant. 



COMBINED OVARY WEIGHT 

 * * IMMATURE 



NON- PREGNANT 



PREGNANT 



SINGLE OVARY WEIGHT 



3 c NON PREGNANT 



« • PREGNANT WITH C.L. 



►•-— • PREGNANT WITHOUT C L 



5 6 7 

 KILOGRAMS 



2 3 



KILOGRAMS 



Text-fig. 1. Frequency distributions of ovary weights. 



Table 1 . Summary of ovary weight records 



Combined weight (kg.) Single weight (kg.) 



Class 



Immature 



Non-pregnant 



Pregnant with corpus luteum ^ 



Pregnant lacking corpus luteum J 



Total 



The increased weight of the ovaries of pregnant females is only partly explained by the presence of 

 the large corpus luteum. The mean weight of 372 corpora lutea was o-88 kg. (see p. 357), and the 

 ovaries of pregnant females weigh on average 1-17 kg. more than those of non-pregnant females. The 

 discrepancy is probably to be accounted for by increased vascularization and increase in follicle size 

 and numbers (see p. 348) which affects both ovaries of pregnant females. 



In two recent seasons (1953/54 and 1955/56) 1146 mature ovaries were weighed separately. The 

 frequency distribution is shown in Text-fig. 1 and the mean weights are set out in Table 1. These 

 figures show that there is a mean difference of about 0-2 kg. between non-pregnant and pregnant 

 ovaries without the corpus luteum, and a difference of about 0-89 kg. between the two ovaries of a 

 pregnant female which is accounted for by the corpus luteum (mean weight o-88 kg.). 



