294 



DISCOVERY REPORTS 



increase as the total length of the whale increases from i6 to 26 m. At about 26 m. 

 in females and 25 m. in males a change occurs in this process and the size of the head 

 begins to decrease in proportion to the rest of the body, as is shown by a sudden 

 turning down of the curve when the greater lengths are reached. 



Contrasting strongly with this we find a lag in growth of the tail region. The curves 

 for measurements of the posterior part of the body (Figs. 11 to 18) are almost mirror 

 images of those for the anterior part. In the graphs of the first two or shorter measure- 

 ments (notch of flukes to dorsal fin, and to anus. Figs. 11 to 14) the lag is less marked 

 than in the two longer measurements (notch of flukes to umbilicus and to ventral 

 grooves. Figs. 15 to 18), so that although the whole tail region undergoes a proportional 

 decrease to compensate for the increase of the head and shoulders, the greatest lag 

 in growth occurs in the region between the anus and the umbilicus. Corresponding 



13-5 M. 



26-3 M. 



Fig. 24. Greatest difference in average relative sizes of the head and tail in small and large 



female Blue whales. 



to the slight reduction in the size of the head at 25 or 26 m., there is a tendency for 

 a slight increase in the size of the tail at about these lengths. 



The proportions of the head and tail in 13-5 m. and 26-5 m. whales are contrasted 

 in the outline sketches in Fig. 24. 



Hinton (191 5, p. 75), dealing with twenty male Humpbacks examined by Barrett- 

 Hamilton, found that measurements of (a) snout to axilla, (b) notch of flukes to penis, 

 (c) notch of flukes to navel, {d) notch of flukes to posterior insertion of the dorsal fin, 

 become relatively shorter as growth proceeds, and concluded that, during adolescence, 

 the thoracic region was the principal seat of growth in the Humpback bull. An 

 examination of the percentage measurements of immature and mature Fin and Blue 

 whales listed by Hinton (pp. 104 and 134) reveals a proportional increase anteriorly 

 and a decrease posteriorly similar to that which has been described above. 



The general conclusion is that with increasing total length, up to a point, the anterior 

 part of the body up to the axilla becomes relatively larger and the posterior part corre- 

 spondingly smaller. It may reasonably be inferred that so long as these steady changes 



