. Text-fig. 38. Ol 234 5678 9 IO II 12 JASONDJFMAMJJ GESTATION PERIOD (MONTHS) Probable growth in length during first pregnancy of females which conceived at the first ovulation. The mean length at conception is taken to be 65-25 ft. (see above, p. 406), but this may be a slightly high (or low) value because females which become pregnant at the first ovulation may be shorter (or longer) than those which ovulate unsuccessfully for the first time. The mean lengths of 86 primiparous females in the 'o corpus albicans' group are set out in Table 14, according to the month of pregnancy, and in Text-
. Text-fig. 38. Ol 234 5678 9 IO II 12 JASONDJFMAMJJ GESTATION PERIOD (MONTHS) Probable growth in length during first pregnancy of females which conceived at the first ovulation. The mean length at conception is taken to be 65-25 ft. (see above, p. 406), but this may be a slightly high (or low) value because females which become pregnant at the first ovulation may be shorter (or longer) than those which ovulate unsuccessfully for the first time. The mean lengths of 86 primiparous females in the 'o corpus albicans' group are set out in Table 14, according to the month of pregnancy, and in Text-fig. 38 the smoothed maternal lengths are plotted against the months of pregnancy, taking July as the mean period of conception. A growth curve has been fitted by inspection to these points taking its origin at a length of 65-25 ft. at conception. There is no statistical justification for fitting an approximately sigmoid curve to the points, but with the exception of the second point, which represents a small sample, the lightly smoothed mean lengths do not show large fluctuations and it is reasonable to suppose that the average curve which has been drawn does approximate to the true growth curve (Text-fig. 38). It is significant that the supposed maternal increase in growth-rate begins about 6-7 months after conception; it is at this time that the exponential phase of foetal growth begins (p. 401, Text-fig. 30) and this increased growth is related to the short annual period of intensive feeding. A mass curve of this kind is likely to reduce apparent changes in the growth rate. It is likely, therefore, though not proven, that fin whales experience a period of increased growth in length, similar to the increase in weight known to take place on the antarctic feeding grounds (Ash, 1956). Probably all fin whales show a similar rapid seasonal increase in length on the feeding grounds, which yearly becomes smaller and smaller until physical maturity is attained. These data suggest th
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