52 



DISCOVERY REPORTS 



Internal genitalia. There is a general similarity between the internal genitalia of the 

 Humpback and the Blue and Fin whales. As a long series of data relating to the repro- 

 ductive processes of this species is not available, the most profitable method of examin- 

 ing the material to hand will be to discuss the observations on each female individually, 

 in order to arrive at a tentative conclusion as to the series of events in the sexual cycle. 

 Before examining the breeding, however, the various organs of the genitalia are reviewed 

 and notes on the conditions found in this species are given. 



Ovaries. The development and anatomy of the ovaries is similar to that of the Blue 

 and Fin whales and consequently need not be described minutely here. They are, how- 

 ever, relatively smaller than in those species, and in the immature stages each pair weighs 

 less than 2 lb., and seldom more than i-^ lb. The ovary weights of immature and mature, 

 but not pregnant. Humpbacks are plotted against body lengths in Fig. 49, where each 

 point represents the weight of the pair of ovaries from one whale. This diagram shows 



to 



■u 



c 



=3 A- 

 o 



rr 



11 

 > 



o 



hp 



CD 



Fig. 



Total Length in metres 



49. Humpback whale. Females. Variation of ovary weight. 



that the weight of the immature ovaries is fairly constant up to a body length of about 

 12-5 m. At this length sexual maturity is reached and indications of increasing weight 

 are then shown. They probably continue to increase thereafter with increasing body 

 length and then to diminish in size in the oldest whales, as in other species, but the data 

 are not sufficient to provide evidence for this. 



As in other Balaenopterid whales, when maturity is reached the ripening follicles pro- 

 ject from the surface of the ovary, one follicle usually being larger than the rest. When 

 ovulation occurs a corpus luteum is formed which remains large and functional during 

 pregnancy. After pregnancy, or soon after ovulation if pregnancy does not take place, 

 the corpus luteum rapidly becomes fibrous and shrinks in size, and then undergoes a 

 process of degeneration so slow that traces of even the oldest corpora lutea probably 

 persist throughout the life of the whale. It has been found convenient in the course of 

 the Discovery investigations to designate the functional corpus luteum of ovulation or 

 pregnancy "corpus luteum a" and the degenerating corpus luteum remaining after 

 pregnancy or unsuccessful ovulation "corpus luteum b" ; this terminology is followed 

 here. The corpus luteum of pregnancy becomes a corpus luteum b at parturition, but 

 that of ovulation not followed by pregnancy has no definite point at which it becomes a 



