SUMMARY 477 



/ _ y^-o (i—e~ °' 45 " -°- 368) ) gives values, for the ages corresponding to birth and weaning, of 

 16-3 and 297 ft. respectively. These are quite close to the observed values and the accelerated 

 growth towards the end of gestation and during the lactation period is, as it were, superimposed on 

 the theoretical curve. 



The existence of such a close correspondence between the theoretical curve and the observed values 

 makes for additional confidence in the figure of 1 -43 for the estimated annual increment of corpora. 



There is, however, one discrepancy which will have been noticed in Text-fig. 60. The estimated 

 value for the mean length at puberty (65-25 ft.), which has been inserted at a point corresponding to 

 an age at puberty of 5 years, is not in agreement with the theoretical curve derived from the von 

 Bertalanfly equation (which in fact gives a value of 67-02 ft. at this age). This requires some explanation. 



Although growth in body length has here been described by a smooth curve, it almost certainly 

 occurs in a series of steps related to the periods of intensive summer feeding in antarctic waters, and 

 partial winter fasting in low latitudes. This was discussed especially for newly mature females, when 

 it was concluded that there was probably a rapid acceleration of growth associated with the summer 

 feeding period (Text-fig. 38). The values from which the theoretical curve has been calculated are mean 

 lengths for females taken during the same period of the year in antarctic waters when feeding on krill, 

 and are therefore directly comparable. The value for the mean length at puberty was inferred from 

 the length frequency distributions of immature and mature females, and is not, therefore, comparable 

 with the other values. The estimated mean age at puberty obtained by a similar method is 5 years, and 

 therefore represents the time of year when growth is thought to be minimal. This partly explains 

 why the length at puberty calculated in this way is below the theoretical curve. Another reason for 

 this is that the data on length and corpora numbers apply to the area 11 sample only, whereas the 

 mean length at puberty was calculated from all available data, representing several areas. There is 

 reason to believe that the length at puberty in area 11 may be slightly higher than the general level 

 in the Antarctic (see also p. 407). 



SUMMARY 



1 . This paper is concerned primarily with female fin whales, Balaenoptera physalus (Linn.), and is 

 based on several thousand whales examined in antarctic waters by or on behalf of 'Discovery' 

 Investigations between 1925 and 1949 and on behalf of the National Institute of Oceanography from 

 195 1 onwards. 



2. In an introductory section, previous work on the reproductive cycle, migratory cycle, growth 

 and age of baleen whales is briefly reviewed. 



The main part of the paper falls into three parts. The first deals mainly with the detailed structure 

 of the ovaries, the evidence for the persistence of corpora albicantia, and the estimated annual rate of 

 accumulation ; the second part describes the annual sexual cycle, and provides a further independent 

 estimate of the rate of ovulation ; the last section is concerned with age-determination by means of 

 the ovarian corpora, and some examples are given to illustrate the application and value of the method. 



3. The mean paired ovary weights of immature, non-pregnant mature and pregnant females are 

 respectively 0-97, 1-97, and 3-14 kg. The increased weight of the ovaries of pregnant females is only 

 partly explained by the development of the corpus luteum. Increased vascularization, and increased 

 follicle size and numbers probably account for the rest. The maximum paired weight of fin whale 

 ovaries was 52 kg., but these were probably in a pathological condition. 



4. The morphology and anatomical relations of immature and adult ovaries are briefly described. 



5. Primary follicles begin to develop in the last 2-3 months of gestation; they are numerous in the 

 cortex of the ovaries of immature females, but are very sparsely distributed in the cortex in sexually 



