AGE EVIDENCE FROM CORPORA LUTEA 417 



From the mature females of 1929-30 there are forty in which the age can be deter- 

 mined in this way. Thirty-five of these belong definitely to the first or second year from 

 sexual maturity, i.e. they constitute Group I of the frequency graph, and five are 

 definitely in their third year (Group II). Now there are fifty-two whales with one, two, 

 three or four corpora lutea (Group I) in the frequency graph (Fig. 3). Thus the overlap 

 from Group II is seventeen, of which five have already been traced. 



5 10 



NUMBER OF CORPORA LUTEA 



Fig. 5. Fin whales, females. Frequency of numbers of corpora lutea. 

 All records from South Georgia since 1924-5. 



CORRELATION OF PHYSICAL MATURITY DATA WITH AGE 

 EVIDENCE FROM CORPORA LUTEA 



In Fig. 3 the physically immature whales are distinguished from the mature, and it 

 is evident that the change takes place between Groups III and IV. Therefore female 

 Fin whales become physically mature between four and six years after sexual maturity, 

 that is, between six and eight years from birth. 



Although this early maturity agrees with the very rapid bodily growth that is known 

 to occur before sexual maturity, it does not suggest very long life. Whether the length 

 of life can ever be more than a subject for speculation is doubtful and, perhaps, for 

 economic purposes the knowledge is not necessary. At least one whale caught this season 

 had attained the age of twenty years (No. 2815), if the average increase in the number 

 of corpora lutea every two years is taken as four. No sign of a climacteric or diminution 

 of fecundity appeared in the ovaries of any whale, not even in those of the whale men- 

 tioned above which possessed forty-six corpora lutea. Nevertheless the largest size and 

 greatest weight of ovary was found in whales with eighteen to twenty corpora lutea, 

 which indicates that after about ten years the reproductive prime is over. 



