228 WHALES AND DOLPHINS 



The dorsal fin, which has a deeply concave hinder margin, is 

 relatively larger and more conspicuous than in either the Blue 

 or the Finner Whale, and the flippers are unusually small, 

 measuring about one-eleventh of the total length. The ventral 

 grooving is distinctive in this whale, for whereas in the other 

 two species just mentioned the grooves extend beyond the 

 navel, in the Sei Whale they are much shorter, and terminate 

 about halfway between the tip of the flipper (when it is 

 placed along the body) and the navel. There is great variation 

 in the number of grooves present. Andrews gives a range of 

 32 to 60, and says that the variation has no relation either to 

 size or to sex. 



The whalebone is very characteristic in the Sei Whale. The 

 blades are mainly black, but a few may be partly white. The 

 frayed inner edges, white in colour, are of a softness, silkiness 

 and fineness of texture not found in any other Rorqual, and 

 the inner aspect of the " side " has been said almost to resemble 

 the fleece of a sheep. 



Hairs are present in small numbers on the upper and lower 

 jaws and on the rostrum. 



The colour of the body is, for the most part, bluish-black. 

 A white area is always present, which stretches backwards 

 from the chin along the under surface, narrows in the region 

 of the insertion of the flippers and then widens out again. 

 This area is subject to very considerable individual variation, 

 but never extends backwards to the tail as it does in the Finner 

 Whale. The under surface of the flukes is never white ; this 

 feature and the pigmentation of the under surface of the 

 flippers help to distinguish the Sei from the Finner Whale, in 

 which these areas are unpigmented. Between the blue-black 

 of the back and the unpigmented under surface the sides are 

 greyish in colour. 



The maximum length attained by this Rorqual is about 

 60 feet, and males and females appear to occur in roughly 

 equal numbers. Andrews says that " observations seem to 

 demonstrate that in the Atlantic, Balcenoptera borealis as a 

 rule breeds early in the spring, but that mating may take 

 place among some individuals at any time of the year". He 

 quotes Millais, who states that " the females probably bring 

 forth their young about November, after a period of gestation 



