. EAR-PLUG AGE (YRS.) Text-fig. 55. Comparison of the ages of individual fin whales estimated from baleen plates and ear-plugs (white, North Atlantic; black, Antarctic). of a biannual formation of laminations was correct. This agreement between baleen plates and ear- plugs was partly confirmed with a small additional sample of antarctic fin whale material collected in 1955-56. The ear-plug ages of this sample (estimated on the basis of two laminations per year) are given by Purves and Mountford (1959) to whom the material was made available. Professor J. T. Ruud and Mr Age Jonsgard (Statens In
. EAR-PLUG AGE (YRS.) Text-fig. 55. Comparison of the ages of individual fin whales estimated from baleen plates and ear-plugs (white, North Atlantic; black, Antarctic). of a biannual formation of laminations was correct. This agreement between baleen plates and ear- plugs was partly confirmed with a small additional sample of antarctic fin whale material collected in 1955-56. The ear-plug ages of this sample (estimated on the basis of two laminations per year) are given by Purves and Mountford (1959) to whom the material was made available. Professor J. T. Ruud and Mr Age Jonsgard (Statens Institutt for Hvalforskning, Oslo) kindly undertook the examina- tion of the baleen plates. In Text-fig. 55 the ear-plug ages are plotted against the ages estimated from the baleen plates. If the age-determinations by these two methods are in exact agreement then the points should fall on the 450 line which is shown. It is apparent that there is fairly close though not exact agreement between these two methods for the first 4-5 years, after which baleen plate ages (owing to wear at the tip of the plates) are supposed to be minimum values. Chittleborough (1959) finds similar agreement between baleen plates and ear-plugs of humpback whales. Purves (1958) and Purves and Mountford (1959) used the assumption that about 1-4 corpora are accumulated annually in the ovaries of fin whales (Laws, 1956a) to confirm the assumed biannual rate of lamina formation in sexually mature females. Some 14-15 corpora accumulate in the ovaries between puberty and physical maturity, and this period is, therefore, estimated to be 10 years (but see p. 388, where attention is drawn to an error in this work). About 12 laminations were found at
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