BREEDING AND GROWTH 413 



numbers of whales are altogether greater in summer than in winter, whereas at the 

 northerly stations the reverse is the case. This fluctuation is described in detail by 

 Risting (1928) and is in itself strong evidence for a northern migration in winter and a 

 southern migration in summer. Harmer has gone into this question in even greater 

 detail, and his analysis of the returns from whaling stations in the Dependencies and on 

 the west and east African coasts puts the fact of the north and south migration of Blue, 

 Fin and Humpback whales practically beyond all question. Of these three species the 

 most rigidly defined migration appears to be that of the Humpback. 



Observations on whales of the North Atlantic have also led to the supposition of a 

 north and south migration, and descriptions of the migrations of these species in that 

 region have been given by Collett (1912), Risting (1928), Hinton (1925) and others. 

 In fact it may be considered that this annual movement is a universal rule among the 

 Balaenopteridae. 



The existing knowledge of the reproductive processes and breeding habits is rather 

 meagre, but a brief account must be given here of the more important previous work 

 which has been done on the subject. 



Work on the breeding of whales which had been published up to 19 15 is mostly sum- 

 marized by Hinton (1925). It may be mentioned that probably the most important early 

 work on the subject is that of Guldberg (1886), to whom reference has already been made 

 on p. 265. Hinton's paper is based on the records of 294 whales examined by Barrett- 

 Hamilton at South Georgia over a period of two months. The value of the material is, 

 of course, restricted by the shortness of the period, for the composition of the local 

 whale population is liable to vary so much from month to month and year to year that 

 conclusions cannot be drawn from a quantitative analysis of the data. In the " Preliminary 

 Memorandum" a scheme of the rate of propagation is given, which summarizes some 

 of the more important conclusions. In this, gestation (in Fin whales) is taken as lasting 

 for 10 to 12 months and the length of the calf at birth as 20 to 25 ft. (i.e. approximately 

 6 or 7 metres); during the next year it is suckling and grows to 45 or 50 ft. (15 metres) 

 and, after weaning, it grows in its second year to 61 ft. and is then ready to breed in the 

 next sexual season. The estimation of the period of gestation and length of the calf at 

 birth appear to be well founded, for there was a considerable number of foetal records 

 and previous work (mostly from the North Atlantic) on which to base the former, 

 and the latter can easily be fixed with sufficient precision from the lengths of the largest 

 foetuses and smallest calves recorded. We have, however, been unable to find any 

 mention of the evidence on which the supposed subsequent rate of growth is based, 

 except a remark on p. 126 that the whalers believe that the calf grows very rapidly and 

 accompanies the mother for a full year. 



According to Haldane (1905) also, the whalers consider that the young Fin whale 

 cow is mature at two to three years. 



Of the Fin whale foetuses noted by Barrett-Hamilton, Hinton estimates the majority 

 to have been conceived in July and August. The majority of pairings for the North 

 Atlantic are estimated to fall between January and April. The Blue whale records for 



