MULTIPAROUS FEMALES 443 



comparatively low latitude, and Fin whales may be plentiful there before they have reached the 

 higher latitudes elsewhere. It is not until about the New Year that the big herds of Fin whales make 

 their appearance on the pelagic grounds' (Mackintosh, 1942, p. 272, and his tables 23 and 24). 

 Rayner (1940, p. 261) showed that fin whales marked near Shag Rocks (just west of South Georgia) 

 were not taken by the South Georgia whalers, but some were taken further south on the pelagic 

 grounds. Fin whales marked and recovered on the South Georgia whaling grounds are found to 

 belong to migrating herds which stop to feed in these waters, averaging about 15 days in the area. 



Similar calculations may be made, basing them on an arbitrary pelagic population, the monthly 

 frequency curve being similar to that for South Georgia, but attaining peak numbers a little later. 

 There is again close agreement between the ascending limb of this curve and the cumulative frequency 

 of ovulations estimated from it, and the cumulative curve again attains the 50% level just before mid- 

 December. 



This hypothesis is not entirely satisfactory in detail. A point which may be raised is that if, as a rule, 

 non-pregnant females ovulate after arriving in antarctic waters, then more cases of very recent ovula- 

 tions should have been observed, in which the follicle is still in the initial collapsed state, or the corpus 

 luteum is in the initial phases of development (see p. 354, Text-fig. 5 a) and has not filled out. Let us 

 suppose that this initial stage lasts about 8 days as in certain ungulates (Harrison, 1948, p. 315). Then 

 if ovulations occur on the whaling grounds some 44% of observed corpora lutea of ovulation are 

 expected to be in this initial phase. Allowing for the large standard error of this percentage a minimum 

 of 16 out of the 59 corpora lutea recorded should have been in this condition. The very early stages, 

 more easily recognizable to observers, should be proportionately fewer. Since the present investiga- 

 tion began in 1954 only 10 recent ovulations have been recorded, and two of these were in the early 

 stages, with the corpus luteum presenting a folded and unexpanded appearance, the original follicle 

 cavity still being discernible (Text-fig. 56). This suggests that they were less than a week old. 

 A number of the early records also note that the corpus luteum looks very young, but fuller details 

 are lacking. It is, therefore, uncertain whether the earliest post-ovulation stages have been observed 

 in antarctic waters, and it is likely that this ovulation usually occurs just before the entry of these 

 females into the whaling grounds. Some 80% of lactating females are believed to wean their calves 

 before they appear on the pelagic grounds (see p. 450). 



It is clear that this problem of the precise relationship of the summer ovulatory period to the 

 lactating and ' resting' phases of the sexual cycle is complex. There can, however, be little doubt that 

 in the fin whale there is as a rule an ovulatory period at the end of, or just after, lactation as in the 

 humpback whale. In contrast to the humpback whale, and related to the shorter duration of lactation, 

 this ovulation in the fin whale occurs during or after a southward migration to the Antarctic, instead 

 of being associated with a northward movement to warm waters. 



Almost without exception it appears to be an unsuccessful ovulation, but there are a few foetuses 

 estimated to have been conceived at this time, in some cases possibly in antarctic waters (p. 403). 

 There are also a few observations of pairing between baleen whales in polar waters in summer. 

 Nishiwaki and Hayashi (1950) described copulation of two humpback whales in antarctic waters in 

 January, and a similar observation was made from a whale catcher by a British Whaling Inspector 

 (J. E. P. Brass) in December 1934, in 6o° S., 95 E. ' I also had the experience of seeing two whales 

 copulating. The pair came to the surface on their sides with flippers securely interlaced' (MS. notes). 

 Unfortunately he gives no details and does not record the species. There are other closely similar, 

 but less reliable accounts by whalers of fin and blue whales seen in coition in antarctic waters. Hinton 

 (1925) refers to reports by whalers of pairing observed in the summer months in the North Atlantic 

 (fin and blue whales off the Finmark coast, pp. 1 18-19, 141). These accounts strongly suggest that 



