i63 DISCOVERY REPORTS 



thicker than in aduhs. Both at Natal and South Georgia the blubber thickness appears 

 to decrease towards the end of the whaling seasons. Pregnant whales are fatter, and 

 lactating ones leaner, than the average, but the difference in this species is not so marked 

 as in balaenopterid whales. 



Cyamus is the only common external parasite of Sperm whales. Penella and Coronula 

 are each recorded once only. Patches of diatom film were frequent on Sperm whales at 

 South Georgia, showing that the whales had spent some time in Antarctic waters. 



Nematode worms very commonly infest the alimentary tract of Sperm whales and 

 occur most frequently in the stomach. The only other internal parasite commonly 

 recorded is Phyllobothrium physeteris, which is nearly always to be found encysted in 

 the blubber. 



The external and internal genitalia of both sexes are described. The histological state 

 of the testes was examined in thirty-six whales, and the results indicate that there is no 

 definite sexual season in the male. 



Dated records of foetal lengths show that the period of gestation is about i6 months 

 and that the young are born at a length of about 4 m. The data do not provide direct 

 evidence as to the length of the period of lactation, but a fresh pregnancy frequently 

 begins before the end of lactation. 



The main part of the pairing season occurs from August to December, with its peak 

 in October. Consequently, most births take place from December to April with a 

 maximum in February. 



The results of a detailed examination of the internal genitalia of fourteen female 

 Sperm whales are given in full. From these it is concluded that breeding takes place 

 once every 2 years, that lactation probably lasts more than 6 months, and that a period 

 of anoestrus is not normally experienced by the female Sperm whale. 



The numbers of old corpora lutea in the ovaries indicate a polyoestrous sexual cycle 

 with an average of three dioestrous cycles and four ovulations at each cycle succeeding 

 the first. 



Sexual maturity is reached at an age of not more than 2 years in the male, and con- 

 siderably less, about 1 5 months, in the case of the female. Physical maturity is probably 

 not reached before an age of 8-9 years, possibly more, in both sexes. Physical maturity 

 as shown by ankylosis of the vertebral epiphyses is very uncommon in the present series 

 of whales. 



Logarithmic plotting of mean values of body measurements against total lengths 

 indicates that the relative growth rates of the anterior part of the body increase and of 

 the posterior part decrease with increasing total length. The majority of the body 

 measurements, however, do not show the simple relation between the relative growth 

 rates of the parts and the total length that is found in some balaenopterid whales. 



The headquarters of the Sperm whale is the tropics, but in summer there is a move- 

 ment towards the temperate regions of the hemisphere concerned. Pairing mainly 

 takes place during this migration and the females give birth to their young in sub- 

 tropical and temperate waters. A small proportion of the males, though fully active 



