THE AGE OF FEMALE BLUE WHALES 227 



since without intensive investigation over many years we are not justified in assuming 

 the recurrent nature of the Antarctic population. 



The legislation of most countries engaging in whaling now provides that no Blue 

 whale under 60 ft. in length may be taken, no female running with a calf or calf accom- 

 panied by an adult may be shot, and the time of commencement and duration of the 

 whaling season in Antarctic waters is determined. These regulations are mentioned 

 because they affect the material, in so far as the data resulting from whaling are no longer 

 an unrestricted sample of the stock. 



The only observation that may have a bearing on the age of an adult male Blue whale 

 is examination of the vertebral column to determine how far ankylosis has progressed, 

 but that in itself is little use in determining the age of an individual after physical 

 maturity is passed. The work of Mackintosh and Wheeler (1929) and Wheeler (1930) 

 showed that the females offered more scope in examination, since the evidence of the 

 breeding cycle could be used in estimating the age of the subject. According to 

 Mackintosh and Wheeler (pp. 389-96) each ovulation gives rise, as in other mammals, to 

 a corpus luteum, which either remains as a functional gland if the ovum is fertilized or 

 rapidly regresses into a corpus albicans, which in Blue and Fin whales shows no sign 

 of being ultimately absorbed. For simplicity in this paper the different classes of corpora 

 will all be referred to as corpora lutea. The corpus luteum of pregnancy also regresses 

 after parturition and becomes indistinguishable from the marks of other ovulations. 

 Thus in these species of whales a permanent record of the number of ovulations is kept 

 in the ovaries and can be used in a study of the life history of the female. The same 

 principles with some modifications have been followed by the writer, and this paper is 

 largely the result of a study of female Blue whales taken in pelagic whaling. 



On board the ' Southern Princess ' I had intended to carry out the same routine 

 examinations as had been in vogue in South Georgia and which I used, inter alia, to 

 investigate the possible similarity between South Georgia whales and those taken on the 

 ice-edge. It soon became apparent, however, that the problem was too cumbrous unless 

 drastic cuts were made in the number of observations on each whale so as to concentrate 

 on those aspects of whaling which bore directly on questions of population and re- 

 production. The general biological interests of the subject had been well served by the 

 investigators in South Georgia. 



In 1932-3 I examined the carcasses of some 700 Blue whales of which approximately 

 one-half were females. Examination of the females was confined to measurement of 

 length, extraction of the ovaries, and estimation of the number of corpora lutea and 

 albicantia thereon, measurement and notation of the sex of the foetus if present, and 

 examination of the vertebral column for evidence of ankylosis. The results of these 

 observations appear below in the section headed "Biological Notes". The condition of 

 the mammary glands was also noted. 



On the basis of the experience gained on this voyage, it was decided that the best 

 results could be obtained by extending the study of the ovaries of adult Blue females to 

 cover a wide field. Thus, instead of gaining some knowledge of the stock of whales in a 



