246 



DISCOVERY REPORTS 



the number of whales in each of these length groups was too small to be a good 



sample. 



The range of corpora lutea numbers found in whales of 78-81 ft. is 0-7, but it is 

 exceptional to find more than three; the average of all the numbers in this group is 1-91. 

 The figures show that whales which were caught at 78 ft. and therefore probably 

 became mature rather late in the preceding winter have succeeded in producing on the 

 average one ovulation, and that the number of ovulations increases with length up to 

 85 ft. It seems likely that the number of ovulations averaged by 81 ft. whales, which 

 probably had a flying start at the breeding season by reason of their forwardness in 

 growth, represents the maximum number of ovulations normally possible in the first 

 sexual season, i.e. 2-60. 



Mackintosh and Wheeler have indicated that there is a fairly definite season of sexual 

 activity (p. 429), and the foetal growth curve above (Fig. 3) corroborates this for pelagic 

 Blue whales. It is impossible to say whether the onset of this activity is a natural 

 internal occurrence coinciding with a certain degree of growth and subsequently 

 regulated by the endocrine balance, as seems to be the case in other mammals, or 

 whether conditions of light and temperature are the chief factors in starting the breeding 

 cycle when the whales migrate towards the tropics. 



Having disposed of the newly mature component in the adult female catch, it remains 

 to find the average number of ovulations performed each year by the remaining adult 

 females. The importance of discriminating between the catch and the total stock of 

 whales, whose constituents may be never fully known, cannot be over-emphasized. But, 

 since the bulk of the material comes from Antarctic waters, we must try to deduce as 

 much as possible about the population in these waters, and, if feasible, extend our specu- 

 lations to include such components as may be absent from the southern regions. 



recent ovulations. The corpus luteum of pregnancy is unmistakable ; it is very large, 

 with a mean diameter of 127 cm., and carries a very pronounced scar with a raised 

 corona, which may be as much as 6 cm. in diameter (Mackintosh and Wheeler, p. 387). 

 In addition to this, there are also found in ovaries old corpora lutea, varying in number, 

 in different stages of regression into the state properly known as corpus albicans. Some 

 of these latter are also large, but are unmistakable because of their dry fibrous structure 

 and the presence of luteal matter, which tinges the regressed corpus yellow. Besides 



