. MONTHS Text-fig. 9. Monthly foetal length frequencies of southern hemisphere fin whales, Balaenoptera physalus; class interval 0-2 m. The estimated mean growth curve is taken from Text-fig. 8. birth length (6-4 m., Mackintosh and Wheeler, 1929) in mid-May, giving a gestation period of just over 11 months. It is considered that this estimate is as accurate as the data permit and that it is unlikely to be more than plus or minus 15 days in error. The reasons for concluding that the fin whale foetal length samples for March and April are biased, must now be presented. First, it should be noted
. MONTHS Text-fig. 9. Monthly foetal length frequencies of southern hemisphere fin whales, Balaenoptera physalus; class interval 0-2 m. The estimated mean growth curve is taken from Text-fig. 8. birth length (6-4 m., Mackintosh and Wheeler, 1929) in mid-May, giving a gestation period of just over 11 months. It is considered that this estimate is as accurate as the data permit and that it is unlikely to be more than plus or minus 15 days in error. The reasons for concluding that the fin whale foetal length samples for March and April are biased, must now be presented. First, it should be noted that almost all the material comes from antarctic waters. In Text-fig. 9 the monthly foetal length frequency distributions are set out in 0-2 m. groups. This figure gives a better idea of the individual variation than the same data presented in Table 2, and it will be noticed that the shape of the frequency distributions changes from month to month and that the relative numbers of larger foetuses appear to be reduced in March. The April sample is really too small to show such a tendency.
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