146 DISCOVERY REPORTS 



the Other hand, if their rate of growth is the same as that of males, they will become 

 mature at a considerably earlier age as shown at point C. Growth continues after 

 sexual maturity is reached until a length of about 11-5 m. is attained. At this length 

 physical maturity is reached and growth stops. The lower unbroken line in Fig. 46 

 shows the growth of the female after sexual maturity. That this line correctly indicates 

 the true course of events in the female is shown by the fact that if the dotted one is 

 accepted the line will have to take a sharp upward curve after point D to allow of growth 

 to physical maturity, whereas it should gradually stop rising, as does the upper line. 

 We may, therefore, say that the female Sperm whale reaches sexual maturity at an age 

 of about 1 5 months from birth, and physical maturity not before 2 years from birth. 

 The early onset of breeding in the female Sperm whale, the length of pregnancy and 

 lactation, and the absence of resting periods intervening between pregnancies, may 

 account in part for the small size of the female when compared with the male. 



Referring now to Table XI in which the commonest frequencies of corpus luteum 

 number are shown to be about i, 4, 8 and 12, it is seen that the ages of the oldest whales 

 recorded, which are only in their fourth breeding season, cannot be more than 9 1 years. 

 This is arrived at by assuming pregnancy to start at the end of the previous lactation ; 

 if any period of anoestrus had been experienced, the age would be correspondingly 

 greater. 



Sperm whales, like the Whalebone whales, reach sexual maturity before growth 

 ceases, as is seen from Table XIV, which shows the state of fusion of the vertebral 

 epiphyses. In only two of the females had the process of ankylosis of the epiphyses even 

 started. In D 179, io-6 m. long, the caudal and posterior lumbar epiphyses were com- 

 pletely ankylosed, but the anterior lumbar and the thoracic epiphyses were still separated 

 from the bodies of the vertebrae by thick cartilage. In D 156, 11-3 m. long, all the epi- 

 physes throughout the column were completely ankylosed. This whale was the largest 

 female Sperm whale examined. Growth in the female evidently ceases at a length of 

 about ii-o to 11-5 m. 



Of the twenty-five males in which the vertebral column was examined there were only 

 two in which any stage of ankylosis of the epiphyses was present. These were No. 3 171, 

 15-35 m. long, in which the posterior lumbar epiphyses were ankylosed with no sign of 

 the join, but the posterior thoracic ones were still separated from the bodies of the 

 vertebrae by thin cartilage; and No. D 121, 1675 m. long, in which the lumbar and 

 posterior thoracic epiphyses were all ankylosed with no sign of the join. The latter whale 

 was the largest of the series but No. 3129, 16-57 m. long, is little shorter and showed no 

 sign of ankylosis in the posterior thoracic vertebrae, in which the epiphyses were 

 separated from the bodies of the vertebrae by thick cartilage. Growth in the male 

 Sperm whale evidently does not normally stop before a length of about 15-5 m. is 

 reached, and probably continues until the whale is 16-5 to 17-5 m. or a little more in 

 length. If the age groups shown for Sperm whales at Natal in Fig. 57, and discussed 

 below, are spaced at yearly intervals, as seems probable, the age of the youngest members 

 of the class of largest whales will be about 5 years. Only two whales of this class showed 



