MULTIPAROUS FEMALES 427 



Africa in June, July and August 1930, recorded details of 16 mature female fin whales. Of these, two 

 were ' resting' but had large maturing follicles up to 5 cm., one was lactating and two were pregnant. 

 Eight had recently ovulated and another probably had recently ovulated; no embryos were found. 

 Two had recent corpora lutea in the ovaries, but it was not possible to ascertain whether they were 

 pregnant or not. 



The two ' resting ' females and the eight or nine whales which had recently ovulated were probably 

 migrating northwards. The appearance and size of the other corpora in these ovaries suggests that in 

 each case these represent either monoestrous cycles or the first of a series of dioestrous cycles. They 

 had not been preceded by recent unsuccessful ovulations. The average size of the largest follicle in these 

 females was only 37 cm., which is very similar to the average maximum follicle size (3-8 ±0-53 cm.) 



M 



M 



J J A S 

 MONTHS 



Text-fig. 44. Relation between month of conception and maternal age. Thin line, mean body length; thick line, resultant; 

 broken line, mean number of corpora. A, all pregnant females ; B, multiparous females. 



in the ' recently ovulated ' group from antarctic waters (p. 348). This close agreement suggests that the 

 follicles are not maturing in preparation for a subsequent ovulation, but may be regressing following 

 the current ovulation. It is interesting that three of the recently ovulated females examined at Durban 

 had experienced multiple ovulations. 



This material, while not providing very strong support for the thesis of monoestrous cycles, does 

 not contradict it. 



The multiparous group may contain some 40 year classes. It has already been mentioned that the 

 ' 3 corpora albicantia ' group conceptions tend to be earlier than those of the ' o, 1 and 2 corpora 

 albicantia' groups. One may ask whether individual females tend to conceive at a slightly earlier date 

 each year so that in general the oldest females are the first to ovulate each breeding season. We are 

 in a position to compare the average ages of females conceiving in each month by using corpora 



