5° 



DISCOVERY REPORTS 



REPRODUCTION 



THE MALE 



External genitalia. The external genitalia of the Humpback are similar in general 

 arrangement to those of the Blue and Fin whales described by Mackintosh and Wheeler 

 (1929). The penis of the male Humpback whale is situated in a groove about 10 per cent 

 of the body length anterior to the anus. In form it does not differ from that of the Fin 

 and Blue whales but it is commonly unpigmented and is smaller, being from 1-25 to 

 2-5 m. in length in the adult. 



Testes. Observations on the testes are recorded from twenty-two Humpback whales. 

 The data available are length, breadth and depth of testis in the complete series ; results 

 of the examination of smears prepared from testis and epididymis in four; and from a 

 further five histological material was preserved from which sections were prepared. 



The measurements of length, breadth and thickness when multiplied together give a 

 value rather in excess of the true volume of the testis, but may be used as an index of 

 the comparative size of the organ. The volume, in thbusands of c.c, is plotted against 

 the total length of the whale in Fig. 48. This shows that the volume of the testis increases 



so- 



u 



u 



u- 

 o 



in 

 O 

 O 

 O 



OJ 



O 

 > 



■+- 



Totdl Length in metres 



Fig. 48. Humpback whale. Males. Variation of testis weight with body length. 



little until a length of about 11 m. is reached. Maturity is reached at about a length of 

 12 m., and between 11 and 12 m. total length the testes tend to increase in size. After 

 maturity is reached no further correlation between volume of testis and length of whale 

 can be traced, some of the large testes appearing to be in no greater state of activity than 

 some of the small ones. Further, no correlation can be established between volume of testis 

 and season of the year. The histological appearances of the immature, inactive mature, 

 and active mature testes are closely similar to those found in the Blue and Fin whales. 

 The sexual cycle. Data as to the histological condition of the testes are available from 

 nine whales. Though this number is very inadequate a detailed consideration of the 



