386 DISCOVERY REPORTS 



In small immature whales the follicles are less than i mm. in diameter, and it is 

 necessary to section the ovaries before they can be seen. In larger whales they become 

 evident as dark round blurrs beneath the surface; and when ripening they project from 

 the surface as thin-walled vesicles 30-50 mm. in diameter (Plate XL, fig. 2). 



The ovum can be obtained from a large follicle by examination of the squeezed-out 

 follicular liquor. It is usually surrounded by follicular nuclei and can just be picked 

 out against a dark background without magnification. An ovum from one of the 

 largest follicles (of a Fin whale) was 0-0165 mm. (0-00065 i'^-) ^^ diameter. The follicle 

 was about 40 mm. in diameter and probably was not fully ripe. 



Among Blue whales follicles measuring as much as 10 cm. in diameter have been 

 found. In one of this size no ovum could be found, but the cloudiness and bad smell 

 of the liquor folliculi suggested that this large size might be a pathological condition. 



In ripening ovaries there are many follicles visible, but usually there is only one of 

 large size. This implies that one ovum is shed at a time, and further that if fertilization 

 does not take place, another follicle ripens and is shed, or in other words that the whale 

 is polyoestrous. 



If more than one ovum were shed at one ovulation, records of two or more foetuses 

 should be more frequent than they are. Only two instances of twins were recorded 

 among the whales examined, and it is possible that these were identical twins, i.e. two 

 foetuses from the same ovum, or from two ova from the same follicle. In one case 

 there was only one corpus luteum of pregnancy, and the six old corpora lutea which 

 were also present were shrunken, hard and small and did not appear to have been 

 concerned in the twin pregnancy. In the other case the internal organs were too decom- 

 posed for examination. There are, however, the following records, among the statistics 

 from South Georgia stations, which seem to show that occasionally several ova are 

 shed at once, viz. seven foetuses in one Blue whale, six in one Fin whale and three 

 in a Sei whale (see Norsk Hvalfangst Tideiide, Sept. 1925, p. 99). Unfortunately, of 

 course, no notes were taken of the condition of the ovaries of these whales, but it 

 seems hardly likely that six or seven twins could develop other than from the discharge 

 of several ova. 



Enlarged follicles are found in a few ovaries during most of the year. Enlargement 

 is sometimes general, both ovaries containing bulging follicles which give a decided 

 impression of coming ripeness. Sometimes one or two follicles of about 20 mm. 

 diameter are visible, while the remainder are very small and hidden beneath the ovarian 

 epithelium. 



In Fig. 124 the diameters of the largest follicles in Fin whale ovaries throughout the 

 year are shown, all records for the seasons 1925, 1926 and 1927 are included. Although 

 the numbers of ovaries examined in diff'erent months vary considerably, it will be seen 

 that the "resting" ovaries, in which only small follicles are present, are commonest 

 in the early months of the year, i.e. the latter part of the southern summer. The ver^' 

 few mature whales taken at Saldanha Bay had large follicles, and three whales which, 

 though exceeding 19-0 m. in length, were still immature (female Fin whales become 



