250 



DISCOVERY REPORTS 



The number of ovulations performed by whales which appeared to have ovulated but 

 did not become pregnant is : 



The recently ovulated but non-pregnant whales show a slightly higher average than the 

 pregnant whales, as might be expected since the occurrence of pregnancy would 

 terminate ovulation. The relationship between the three classes and their effects on the 

 average number of ovulations performed by the whole group is shown in the following 

 table: 



It is perhaps of interest to note in passing that the sample showing the highest rate 

 of ovulation and the highest percentage of pregnancy came from the ' New Sevilla ', 

 which was working in the Weddell Area, while the other three came from the adjacent 

 Bouvet Area. The point is mentioned because the number of ovulations may vary with 

 whales from different regions or migrating from different breeding grounds. This is, 

 however, the purest speculation. 



The figures in the above table show that the average number of recent ovulations in 

 each sample is mainly a function of the pregnant and resting whales, the whales which 

 have recently ovulated without being fertilized forming a relatively insignificant class. 



These results suggest, if there is enough material to be significant, that the increment 

 of corpora lutea in a catch of whales in which the percentages of pregnant and resting 

 whales are 50-79 per cent and 12-42 per cent respectively, as is true of most catches, is 

 in the region of one per annum after the first adult season (when the average number is 

 1-91, see p. 246). The average number of recent ovulations for the whole of the mature 

 material considered above is 1-13. 



Corroboration of such figures is found when corpora lutea frequencies are dealt with 

 in the next section. In order to apply this conclusion to the whole Antarctic stock, it is 



