2o 4 DISCOVERY REPORTS 



backs, distinguished by the relative amount of dark and light pigment and originally 

 described by Lillie (1915). He shows that while individuals of different colour groups 

 mingle freely with one another, there is some evidence that in different parts of the 

 world the proportions of the various colour classes may differ more or less constantly 

 within the schools. This point is referred to again on p. 246. Matthews, however, agrees 

 with Olsen's opinion (1914-15) that 'having regard to the extraordinary variability of 

 the Humpback in the matter of colour, one can scarcely attribute much systematic 

 importance to this character '. 



Whalers in the Antarctic speak of the Myrbjonner as a distinct race of Blue whales. 

 These are small whales which appear to be distinguished by a large quantity of pale 

 spots on the dorsal surface. They are commonly noticed on the whaling grounds east of 

 the Greenwich meridian, and are sometimes held to be fully grown. They may represent 

 a colour variety of Blue whales, for there is some variation in the quantity of pale spots 

 in this species ; but it seems certain that they are not fully grown. Mr P. R. Crimp, who 

 has undertaken a considerable series of biological investigations in factory ships, has 

 examined examples of Myrbjonner, and by inspection of the reproductive organs has 

 found them always to be sexually immature. Certain small Fin whales have been 

 similarly distinguished. These are of a darker shade than others, with the pigment 

 spreading a little farther round the ventral surface, and they are said to be common 

 around Graham Land and the South Shetland Islands. These again Mr Crimp has 

 found to be sexually immature, and it must be supposed that they also represent a 

 colour variety which is perhaps more noticeable in immature than in adult whales. 



SIZE RANGE 



There is little material for an accurate estimation of the average size at birth of any 

 of the species of whalebone whales. Mackintosh and Wheeler (1929) take the mean 

 length of Blue and Fin whales at birth as 7-0 m. (23-0 ft.) and 6-5 m. (21-3 ft.) re- 

 spectively. These figures were based on available records of the largest foetuses and 

 smallest calves, and there is nothing in the Discovery Committee's more recent records 

 to suggest modification of these figures except for one Blue whale foetus (of whale 

 no. 1761) which measured 7-46 m. (24-5 ft.). The International Statistics quote a few 

 instances of Blue whale foetuses measuring between 7 and 8 m., but these are very rare, 

 and I can find only two records of Fin whale foetuses exceeding about 6-7 m. (22 ft.). 

 The Statistics do not mention any very small calves, but the (earlier) British Museum 

 Statistics record a Blue whale calf of 77 m. and three Fin whales measuring between 

 7 and 8 m. It is not to be expected that the length at birth is always exactly the same 

 in any one species, and Blue and Fin foetuses exceeding 7-0 and 6-5 m. are probably 

 above the average of this length. If it were worth while for the whalers to take the 

 youngest calves we might well find a few measuring a little less than 7-0 and 6-5 m. It 

 appears then that these lengths are not far from the true average lengths at birth, and 

 in the absence of more precise data they may provisionally be accepted as correct. 



Matthews (1937) estimates that Humpbacks are born at a length of about 4-5-5-0 m., 



