136 



PROBLEMS OF RELATIVE GROWTH 



length increases steadily from small foetuses to large whales 

 25 metres long (at extreme sizes it appears to fall again slightly). 

 Similarly, the relative tail-length decreases with absolute size, 

 from the juvenile stage onwards. The results are essentially 

 similar in Blue and Fin whales (Balaenoptera musculus and 

 B. physalis). Measurements of two dimensions are herewith 

 given for male Blue whales. 



TABLE XII 



Relative Head- and Tail-lengths in Male Blue Whales (Balaen- 

 optera musculus) from S. Georgia (from Mackintosh and Wheeler, 

 1929 



This is precisely the opposite of what is found by Scammon. 

 Clearly the head is endowed with a specific heterogony which 

 counteracts the effect of its precocious development, and, from 

 the foetal stage on, overrides the effect of the tail's later 

 differentiation. 



In passing, it may be mentioned that the measurements 

 given by Mackintosh and Wheeler could furnish a rich mine 

 of information for constructing growth-profiles for both sexes 

 of the two species of whale. Unfortunately, only percentage 

 measurements are given for the means, and without mean 

 absolute measurements for the total length classes. For 

 accurate work it would accordingly be necessary to recalculate 

 the original absolute data in the appendices. 



