254 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
of a mark from a whale which Rayner estimated to be about 40-45 
feet long at the time of marking, and which measured 68 feet 9 inches 
when it was killed 214 years later, suggests growth to maturity in 2 
or 3 years. It is to be hoped that further evidence, perhaps from the 
marking of whales, will be forthcoming in the future. 
Up to a point, length is correlated with age, for growth continues 
after sexual maturity and ends when full physical maturity is 
reached. This is the point at which all the epiphyses of the vertebrae 
have become fused to the centra, a process which in whales takes place 
at a relatively early stage in the caudal region, and is finally completed 
among the anterior thoracics. 
That the accumulations of old corpora lutea are indicative of the 
age of an adult female is shown first by the fact that whales measur- 
ing not much more than the average length at sexual maturity always 
have comparatively few corpora lutea, while larger whales have 
various numbers up to 50 or more, and secondly by the fact that there 
is a close correlation (in blue and fin whales) between the number of 
corpora lutea and the attainment of physical maturity. Wheeler 
(1930) found that fin whales with less than 15 corpora lutea were 
nearly always physically immature, and those with more than 15 
nearly always mature. The corresponding number in blue whales 
according to Laurie (1937) is 11. More recent data, not yet published, 
suggest, however, that this figure should be a little higher. Since 
whales appear to be polyoestrous there might be one or more ovula- 
tions in each breeding season, with consequent variations in the rate 
of accumulation of corpora lutea. The correlation, however, between 
physical maturity and numbers of corpora lutea suggests that there 
is in fact a fairly steady annual increment. The actual number of 
years represented (on the average) by a given number of corpora 
lutea is still, however, in doubt. From the frequencies of numbers of 
corpora lutea Wheeler inferred that fin whales become physically 
mature 4-6 years after sexual maturity, which implies about three 
corpora lutea per annum. Laurie, by a different method, estimated, 
however, that in blue whales the rate of increment is slightly more 
than one perannum. A fin whale which was killed 6 years after it had 
been marked had only eight corpora lutea (Mackintosh, 1942), and in 
this particular whale the rate cannot have been much more than one 
per annum. The majority of blue and fin whales taken m the Ant- 
arctic are physically immature, and even if only one corpus luteum is 
added each year, the majority are presumably less than, say, 20 years 
old. However, it is not yet finally proved that the rate of accumula- 
tion cannot be less than one each year, or that none of the oldest cor- 
pora lutea disappear in the oldest whales. The largest number found 
so far is 54 in a fin whale. 
