2 6 4 DISCOVERY REPORTS 



in Fig. 8, p. 272 that the testis tubules of most whales have reached a diameter appropriate to mature 



individuals by the time they are about 9-5 m. in length. 



Of the ninety-three whales, thirteen were judged to be immature. In sections of testis from certain 

 whales there was more or less immature tissue present in addition to mature tissue : these whales were 

 F33, 7-8 m.; F247, 9-5 m.; F319, 9-8 m.; F321, 10-9 m.; F289, 11-3 m.; and F20, 14-6 m. Presum- 

 ably they were recently mature. Tissue from the two longest immature whales (F226, 12-2 m., and 

 F3, 12-5 m.) seemed to be approaching maturity: all the tubules were open and in a few there were 

 spermatocytes present. 



Table 18. Males. Lengths of sexually mature and immature whales examined at Horta in 1949, 1953 and 

 1954. Maturity was determined by histological examination of the testes. The larger mature whales 

 are omitted 



Mature Lengths in m. Immature Mature 



1 

 4 

 4 

 2 



3 



4 

 2 



2 



3 

 2 



1 

 1 

 1 

 1 



4 

 1 I3-8-I3-9 l 



1 14-0-14-1 — 2 



4 

 4 

 2 



3 



The lengths of sexually mature and immature whales are shown in Table 18. Although most 

 whales larger than 9-5 m. were mature, the table shows a considerable overlap, the smallest mature and 

 the largest immature whale being 7-8 m. (26 ft.) and 12-5 m. (41 ft.) long respectively. All sperm whales 

 cannot be expected to mature at the same length, but, so far as one may judge from comparable tables 

 for whalebone whales (Mackintosh, 1942, p. 218), the present overlap is perhaps more than might be 

 expected. There is always the possibility of a clerical error here and there in recording measurements 

 and noting collections under the difficult conditions of the flensing platform, but Senhor Reis' 

 methods are so careful that I think such mistakes are unlikely. By inspection of present figures it is 

 difficult to judge the 'best' value in Table 18 for a mean length at which males become sexually 

 mature. It is put here at 9-6 m. (31 ft.) which makes some allowance for the overlap. It is not more 

 than 9-6 m. and may be less, for at present there is information on only three whales of lengths 

 between 8-o and 9-5 m. 



For guidance in the field it may be noted from Fig. 4 that sperm whales of the North Atlantic may 

 be considered mature if the combined volumes of their testes amount to 3-5 1. or more. (This state- 



