THE SEI WHALE 263 



posterior lumbar epiphyses were ankylosed, as were the anterior thoracic. The middle 

 lumbar epiphyses were separated from the bodies of the vertebrae by thin cartilage, 

 and those of the anterior lumbar and posterior thoracic by thick cartilage. 



As will be seen from the table the number of recognizable ages of scars gives little, if 

 any, indication of the age of the whale. Each distinct age of scars may represent a 

 migration into warmer waters, but after a few years the older scars become very 

 indistinct and confused, so that no conclusions of any value can be drawn from their 

 presence. The migrations of this species are, too, as shown below, less extensive than 

 those of the larger Rorquals, so that different ages of scars may be produced without 

 the occurrence of lengthy southward migrations between them. This is seen in whale 

 D 123 which was aged about 2 years, but carried 5 recognisable ages of scars. 



Turning now to Tables VI, VII, VIII and IX, which show the mean values of the 

 measurements of different parts of the body according to the length of the whale (in 

 roman type), an indication of the relative rates of growth of the various parts may be 

 obtained. If the mean values of the various measurements are plotted against the total 

 length of the whale on a double logarithmic scale, the results shown in Figs. 86-104 

 are obtained. Measurements for South Georgian whales only are used, and the values 

 for males and females are distinguished. In each of these figures the points are obviously 

 falling about a straight line, and in some of them the approximation is very close. This 

 being so, it may be taken that the rates of growth of the various parts of the body 

 relative to the total length satisfy the equation j = 6:*;'^ , where x is the total length, y the 

 length of the part, b the fractional co-efficient (the value of j when :x;=i) and k the 

 growth co-efficient. The values of ^ for each measurement are shown in Table XXIV. 

 Values of k over unity indicate an increasing rate of relative growth and those less than 

 unity the converse. In only three cases has k a value over unity, for measurement 

 No. 3, tip of snout to blow-hole; No. 6, tip of snout to tip of flipper; and No. 15, length 

 of base of dorsal fin. The latter may be dismissed as of little significance because the 

 measurement is taken between ill-defined points and is thus liable to considerable error. 

 The first, however, measurement No. 3, shows that as the whale increases in total 

 length the relative rate of growth of the rostrum increases : the second, measurement 

 No. 6, appears to indicate a high growth rate not only in the rostrum but also in the 

 anterior thoracic region. The difference in the relative growth rates shown by the Sei 

 whale, when compared with those of other balaenopterid whales, particularly the 

 Humpback whale, are striking. In them there is a very marked increase in the relative 

 growth rates of the anterior part of the body, and decrease in those of the posterior 

 part, as total length increases. In the Sei whale, however, nearly all the measurements 

 show a decreasing relative growth rate with increasing length, so that the body pro- 

 portions of large and small whales are not greatly different, as was shown in an earlier 

 section when considering the percentage values of the body measurements. This 

 relative consistency of proportions is rather unexpected in view of the characteristic 

 change of proportions found in other whalebone whales. In them the growth of the 

 whale appears to be largely concentrated on developing the mouth and baleen apparatus. 



