334 DISCOVERY REPORTS 



length, and size of foetus if present were recorded. In 1954/55 and 1955/56 a further 159 pairs of 

 ovaries were collected by whaling inspectors and biologists in the three British floating factories and 

 numerous other observations were made. The methods of examining this material have been 

 standardized and it has provided much of the data for this paper. 



In addition to this recent material I have had access to the records kept by the ' Discovery ' 

 Investigations from 1925 onwards (since 1949 incorporated in the National Institute of Oceanography). 

 The data which are of relevance here consist mainly of observations of length, physical and sexual 

 condition, state of fusion of the vertebral epiphyses, counts of the number of corpora lutea and 

 albicantia, some measurements of the dimensions of these bodies, and measurements of the genitalia 

 and foetuses. There are in addition limited collections of ovarian and testis material. The most 

 important part of this varied material is in the form of counts of the ovarian corpora made by no less 

 than fifteen different observers. One consequence of this is that there is a considerable variation in 

 the quality of the work, since the different workers have applied different methods and criteria. It is 

 difficult to make allowance for these variations and although all the records have been freely used in the 

 course of the work it is preferable, where possible, to rely mainly on the more recent material to 

 illustrate the present paper. For this reason there are discrepancies in amount of material between 

 the various tables in this paper, but it is scarcely practicable or necessary to explain these discrepancies 

 in every case. 



Previous work 



The first comprehensive studies of southern hemisphere fin whales were undertaken by the ' Discovery ' 

 Investigations in 1925, although Barrett-Hamilton (Hinton, 1925) had examined some 300 whales at 

 South Georgia in 191 3/14. This early work and later research by various workers up to 1940 is reviewed 

 by Mackintosh (1942). The anatomy of the urino-genital system of fin whales has been described by 

 Ommanney (1932) who dissected four foetuses. 



Mackintosh and Wheeler (1929) worked at South Georgia and Saldanha Bay and their paper based 

 on 1577 fin and blue whales established the general outline of the biology of these species and remains 

 the most important single source of information on the biology of the fin whale. Consideration of the 

 time of follicular ripening ; the occurrence of corpora lutea of ovulation, and minute foetuses ; the 

 onset of increased testis activity in males, all suggested the earlier part of the southern winter as the 

 beginning of the breeding season. These workers plotted foetal lengths, drew a mean growth curve, 

 and by assuming all foetuses grow at the same speed they calculated the proportions conceived in 

 different months. The majority of pairings appeared to take place in June and July and the gestation 

 period was estimated to be just under a year. From the sizes of the largest foetuses and smallest 

 calves they concluded that the average neonatal length of fin whales is 6-5 m. The length of the calf 

 at weaning was estimated in a similar fashion to be about 12 m. and the lactation period to last about 

 6 months on average, from mid-June to early December. From these conclusions and because 

 approximately half of the adult females they examined were pregnant they decided that each breeding 

 cycle usually lasted 2 years. However, Wheeler (1930) was aware that in the fin whale a post-partum 

 ovulation can result in one pregnancy being followed immediately by a second. From an examination 

 of length frequencies they concluded that it was likely that both blue and fin whales attained sexual 

 maturity at an average age of 2 years, and they gave figures for the average body length at sexual 

 maturity for both sexes. 



They showed that in general the number of corpora lutea and corpora albicantia in the ovaries 

 increased with increasing body length, which suggested that corpora albicantia persist and accumulate 

 in the ovaries during life. Ovulation was shown to be spontaneous, and they advanced arguments for 



