BREEDING AND GROWTH 421 



It has already been shown that large follicles may be present at any season of the year 

 in whales which are neither pregnant nor lactating, but there is definite evidence that 

 in the majority of such whales the follicles are small during January, February and 

 March, but increase in size in April and May, i.e. the growth of the follicles eases up 

 in the summer but becomes active at the commencement of the southern winter (see 

 Fig. 124, p. 387). 



Perhaps the most important sign of breeding activity is the occurrence of functional 

 corpora lutea in the ovaries without the presence of a foetus. This, of course, indicates 

 recent ovulation. It is observed so seldom at South Georgia that the occurrence of a 

 recent corpus luteum in the ovaries almost invariably means a foetus in the uterus. At 

 Saldanha Bay, however, such corpora lutea occurred comparatively frequently in pro- 

 portion to the number of adult whales. 



Although these corpora lutea of ovulation have been discussed in the section on the 

 reproductive organs it will be convenient to recapitulate here some of the details of their 

 occurrence. Among Blue whales they were found on March 14 and 18 (1926 and 1927), 

 May 4 (1925), and October 24 (1925) at South Georgia; while among the few mature 

 whales at Saldanha Bay they occurred on June 17, 22 and 29 and on July 19. Among 

 Fin whales they were found on February 16 and 28 (1925) at South Georgia, and June 22, 

 July 13 and September 15 at South Africa. It must be emphasized again that the 

 numbers of adult females taken at South African stations is very small and that the 

 percentage of ovulations is therefore very high. 



Further light is thrown on the breeding season by the occurrence of several minute 

 foetuses in an early stage of development. Two of these were of Blue whales and 

 occurred in July and August. They measured 21 mm. and 30 mm. respectively. It is 

 difficult to say how old such foetuses are but probably conception took place not less 

 than several weeks previously. Among Fin whales there were three small embryos. 

 One of these was found in August and the other two both occurred in January. Judging 

 from the appearance of one of the latter when it was found (in whale No. 331) it seems 

 possible that it was abortive, but the occurrence of the other one so late as January 

 is surprising, though not very exceptional when compared with the irregular occurrence 

 of many of the larger Fin whale foetuses (see Fig. 146, p. 425). Photographs of some 

 of these foetuses appear on Plate XXXVIII, together with that of a Sei whale (No. 1074) 

 which measured only 2 mm. and is probably the smallest foetus of a whalebone whale 

 which has ever been found. These small foetuses are not described in detail in the 

 present report but will doubtless form the subject of a separate paper in due course. 



It has already been explained that through the greater part of the year the testis is 

 in a comparatively quiescent condition but that from about April to July it shows signs 

 of increasing activity in the production of spermatozoa (see p. 408). Seen as it is in 

 sections of the testis, this activity takes place perhaps rather earlier than one would 

 expect, comparing it with, say, the time at which corpora lutea of ovulation occur most 

 plentifully, but a proliferation of germ cells in the testis does not, after all, necessarily 

 mean that the spermatozoa will be put to immediate use. 



