TOOTHED WHALES 287 



For example, in the sheep WtQ = 2i^-6 days and LtQ = 2i days. In the present paper Lt^ is assumed to 

 be 0-9 X WtQ, and Huggett and Widdas's scale of estimates of Wt^ is converted by this factor. 



Huggett and Widdas state that the growth velocity found by their method for blue and fin whales 

 is 'at least 2^ times greater than the highest rate found for all other mammals, and about 10 times 

 greater than the rate for Primates '. They remark that it ' would be interesting to see if these high rates 

 are peculiar to the large whales or are the same in related species of smaller size'. It is generally 

 considered that the Odontocetes are on average on a lower grade than Mysticetes (Simpson, 1945) 

 and in general they are smaller, so they will now be discussed in this order. Conspicuous modifications 

 in the shape as well as the magnitude of the foetal growth curves of the Mysticetes as compared with 

 the Odontocetes then become apparent. 



TOOTHED WHALES (ODONTOCETI) 

 Data on the foetal growth of the sperm whale given by Matthews (19380), Mizue and Jimbo (1950), 

 and Clarke (1956) have been used. As the full original data are not given the mean monthly foetal 

 lengths have been taken from the graphs and the Japanese measurements have been converted from 



• SANRIKU 

 o HOKKAIDO 

 a AZORES 



UJ 



I 

 I- 

 o 



z 



M 



D J F 



'—•"^ MONTHS 



Text-fig. 2. Foetal growth in length of northern hemisphere sperm whale, Physeter catodon (points represent monthly means). 

 In drawing the average growth curve only the North Pacific data have been used. 



feet to metres in the interests of uniformity. Although great care was exercised, some small errors 

 may have resulted from this treatment, but it is thought that they do not affect the conclusions 



drawn. 



These data are set out graphically for northern and southern hemisphere sperm whales in Text- 

 figs. 2 and 3. The average neonatal lengths are taken to be 3-92 m. in the northern hemisphere (Clarke, 

 1956) and 4-15 m. in the southern hemisphere (Matthews, 1938a, p. 138, '4 metres or a little more'). 

 Lines representing the average rate of growth have been fitted by inspection, slightly weighted to 

 allow for the variation in size of the monthly samples. Both northern and southern hemisphere data 

 suggest that growth is linear for most of gestation. For the northern data the length of the period 

 {tg-Q is 15 months, or 457 days. If the neonatal length of southern hemisphere sperm whales is 



