4o6 DISCOVERY REPORTS 



Several authors have suggested that the length of life of an animal bears a direct 

 relation to the length of the period of its growth. Lankester (1870) discusses this ques- 

 tion, and mentions the 5 to i ratio advanced by Flourens (see Grindon, 1863), and the 

 6 or 7 to I ratio previously put forward by Buffon (1775). Flourens states that the 

 Right whale lives for 300 years, but does not give the length of the period of growth 

 or the source of this information. The period of growth was calculated as 20 to 25 years 

 by Dewhurst (1834, p. 23) from notches in the baleen. Later estimates based upon 

 greater practical knowledge include those of Scammon (1874) and Haldane (1905). The 

 former (p. 18) considered that the natural term of life was from 30 to 100 years'; the 

 latter (p. 71) that the limit was reached at about 40 years. 



Two observations mentioned by Allen (1916) are of interest. He notes that Sibbald 

 refers to a Sulphurbottom whale recognized by fishermen in the Firth of Forth for 

 20 years before it was cast ashore in 1692, and also that Verrill (1902) mentions a 

 Humpback, known by a peculiar whistle caused by a large barnacle on its blowhole, 

 that appeared regularly in the Bay of Fundy for 20 years. 



The age at sexual maturity is known to be two years from birth (Mackintosh and 

 Wheeler, 1929). Economically it is the years following sexual maturity that are im- 

 portant, for from this time onward the female is believed to give birth to a calf not 

 more often than once in every second year, with the result that the whale population 

 will not increase unless the females are allowed to live for at least four years after sexual 

 maturity. 



In the previous report (1929) a theory was advanced that the accumulations of scar 

 tissue due to the degeneration of corpora lutea might give a clue to age in females for 

 at least several successive seasons following maturity. Further data on this point were 

 obtained by Messrs F. C. Fraser and G. W. Rayner during seasons 1927-8 and 1928-9, 

 and by Mr F. D. Ommanney and myself during 1929-30. Recently we have found 

 it possible to study also the ankylosis of the vertebral epiphyses with their centra, thus 

 gaining indications of the degree of physical maturity which has been attained ; and it is 

 with this work, correlated with that yielded by further study of the corpora lutea, that 

 this paper is mainly concerned. 



It may be mentioned that indications of age were again sought for in the ridges of 

 the baleen plates, the structure of bone, and the scars of parasite wounds in the epidermis. 

 Of these the last only was suggestive, but to a very limited and uncertain extent. 



While working on the formation of the corpora lutea the question of multiple ovula- 

 tions, i.e. more than one ovum liberated at one ovulation, appeared to be of some im- 

 portance. This subject is dealt with in the note on p. 419. 



