NEWLY MATURE FEMALES 41S 



The mean growth curve has been continued as a broken line, increasing very slightly from June to 

 December and then increasing again during the second feeding season after puberty. At 2 years after 

 puberty the mean length is shown as 69-6 ft. If the average rate of ovulation is 1-4 per year (below 

 p. 465) then 2 years after puberty there are expected to be on average 2-8 corpora and from Text- 

 fig. 25 the mean length at 2-8 corpora is 69-6 ft. The growth previous to puberty is also suggested as 

 a broken line, to indicate that in the feeding season before puberty growth is more rapid, as is probable 

 in the primiparous feeding females. If this line of argument is correct, then puberty usually succeeds 

 both a period of rapid growth, and a northward migration when day length is increasing (see below, 

 p. 421). 



72 -1 A - - BC - — DF- 



'jvTa mJJaSONDJFMAMJJASONDJFMAMJ 



MONTHS 



FEEDING PAIRING 



FEEDING PARTURITION 



FEEDING 



-| 



Text-fig. 39. Growth of newly mature females indicated by mean length ± a, ±2 s.E. A, at puberty; B, first pregnancy, 

 o corpus albicans ;C, one nulliparous ovulation ; D, first lactation or resting period; F, second pregnancy, 1 corpus albicans. 

 See text for explanation. 



The position of the remaining group, of females in their second pregnancy with one corpus 

 albicans and resting mammary glands (F), must now be discussed. These are females which have 

 become pregnant again at the first ovulation after the termination of the first pregnancy. It seems 

 most probable that the origin of this second pregnancy is either a post-partum ovulation (shown below, 

 p. 429, to be a normal feature of the reproductive cycle in female fin whales and some other species) 

 and or an ovulation following the termination of lactation upon loss of the calf. It is, however, certain 

 that some, possibly all, of these first-lactation females do not experience a post-partum ovulatory 

 period and that some or all of them are a year older than has been indicated in Text-fig. 39. It is only 

 possible to diagnose accurately the reproductive history of those females in the first lactation or 

 resting period which have only one corpus albicans in the ovaries. None of the individuals in this 

 group has, by definition, experienced a post-partum ovulation. Those with more than one corpus 

 in the ovaries might possibly be in the second lactation or resting period, but there are undoubtedly 

 many females in their first lactation or resting period which have more than one corpus albicans in 

 their ovaries and some of these may well have experienced a post-partum ovulatory period. The fact 



