THE LENGTH/WEIGHT RELATIONSHIP 303 



Zemskiy (19506, figs. 2, 3) demonstrated this by means of detailed measurements of sixty-six 

 fin whale embryos between 49-5 and 569 cm. in length. He took five series of measurements (snout- 

 umbilicus ; snout-anus ; head length ; pectoral girth ; anal girth) and showed that the ratio of these 

 measurements to body length (expressed as percentages) remained more or less constant within this 

 range of foetal lengths. The smaller series of foetal measurements given by Mackintosh and Wheeler 

 (1929, pp. 324-29) are in very close agreement. These authors also give the results of similar measure- 

 ments on over 600 post-natal fin whales. Their mean percentage values for these three linear proportions 

 in adults are very close to the mean values for foetuses and well within the foetal ranges. 



Zemskiy states that the throat grooves (a special feature of the rorquals) first become apparent at a 

 length of i-o m., and become distinct and similar in appearance to those of the adult at a length of 

 1-5 m. The baleen is first discernible externally in embryos of about 3-o-4-o m. (Mackintosh and 

 Wheeler, 1929, fig. 96; Zemskiy, 1950). 



10,000 



LENGTH IN METRES 



Text-fig. 13. Plot of foetal weight against length for 234 blue, fin and sei whales (black circles), nine humpback whales 

 (white circles), and ninety-three porpoises (crosses = monthly mean values). Regression lines have been fitted by eye 

 and the neonatal values for blue, fin and humpback whales are indicated. 



In the last 5 months of pregnancy the blue whale foetus grows in length from 1-3 to 7-0 m., corre- 

 sponding to an increase in weight of 2480 kg. (from 20 to 2500 kg.) or 2-44 tons. In the last two 

 months of pregnancy the average gain in weight is over 2 tons (420-2500 kg). The gro\vth rate of the 

 fin whale is of the same order of magnitude. In some individual blue whales the growth rate is prob- 

 ably even greater ; the largest blue whale foetus (PI. XIII, fig. 2) measured 7-46 m. and must have weighed 

 about 2800 kg. (275 tons). 



Expressed in this way the foetal growth rate of the baleen whales is seen to be phenomenally rapid, 

 and without parallel. 



