246 DISCOVERY REPORTS 



of corpora lutea, those of the largest do not contain the greatest numbers. This is to 

 be explained by the persistence of the corpora lutea through several sexual seasons, and 

 probably throughout the life of the whale, so that adult whales of similar length but 

 different ages will have different numbers of corpora lutea in their ovaries. 



Uterus. The distance across the uterine cornu was measured in seventy-four Sei 

 whales and the figures obtained are plotted against total length of whale in Fig. 72. 

 The measurement was taken from side to side across the collapsed cornu when lying 

 on a flat surface. It is thus rather greater than the true diameter. Measurements from 

 immature, mature but resting, ovulating and lactating whales are separated. This 



30- 





20- 



(TJ 



o 



a 



o 

 U 



o 



10- 











• •• • 



• • ••• ^ 



•Ml • M mm * 



• •• * • 

 • •• • • • 



• ••«•«• • • 



• «»• • 



• •••• • 



• •• • 



M ••• •••• • 



14 



~r 



— r- 

 16 



18 



Total Length in metres 



Fig. 71. Sei whale. Females. Numbers of corpora lutea. 



distance increases slowly with total length of the whale up to the attainment of sexual 

 maturity at about 14-5 m., after which it is increased, often considerably, and rarely 

 returns to less than about 10 cm. From the data available no correlation can be traced 

 between the size of the uterus and the stage of the sexual cycle through which the whale 

 is passing. 



Mammary glands. The situation of the mammary glands on either side of the mid- 

 ventral line, with the teats at each side of the genital groove, is similar to that of other 

 balaenopterid whales. The thickness of the gland in cm. is plotted against total length 

 of whale in Fig. 73, three stages of activity being represented, non-parous, involuted 

 and lactating. The non-parous gland varies in thickness from 2 to 4 cm. and rarely is 



