33 6 DISCOVERY REPORTS 



corpora in the ovaries with the results of baleen readings and found them to be in agreement with the 

 findings of Mackintosh and Wheeler. He suggested that in the breeding season up to 6-7 ovulations 

 are possible before pregnancy supervenes. In the light of these estimates of age he suggested that the 

 age at sexual maturity was more likely to be 3 years than 2. 



Mackintosh (1942) gave a valuable summary of all aspects of the biology of whalebone whales. He 

 had little to add to the earlier work on reproduction and age, though in the light of accumulated data 

 he made some slight amendments to the average lengths at sexual maturity. He was also able to give 

 particulars of a very important whale mark recovered in 1941 which had been carried by a female fin 

 whale for 6 years. The ovaries were recovered and had eight corpora. As there is no reason to suppose 

 this whale was conspicuously immature when marked, he concluded that in this individual ' the rate 

 of accumulation cannot have been much more than one a year (or two every 2 years), and, since there 

 was no clue to the whale's age at the time of marking the rate of accumulation may have been even 

 slower' (p. 227). On the other hand, if this female was immature when marked then the incremental 

 rate could have been higher. This is hardly compatible with Wheeler's estimate, but it is in agreement 

 with Peters's (1939) calculations. 



Peters claimed that, as there was a very great difference in the development and activity of the 

 corpus luteum of pregnancy and of ovulation, he had been able to establish morphological and histo- 

 logical criteria for distinguishing the corpora albicantia representing pregnancies and ovulations. By 

 counting the former and assuming a 2-year reproductive cycle he provisionally estimated that in 

 the fin whale there is an average of i-8 ovulations in 2 years, and in the blue whale 1-9 ovulations. 

 Consideration of his criteria, the colour and texture of the gland and the arrangement of the connective 

 tissue trabeculae, suggest that he was confusing the various stages of regression (see below, p. 384). 

 Nor is there such a marked difference between the corpora lutea of pregnancy and ovulation as he 

 states. No other workers have been able to make such a distinction between the types of corpora 

 albicantia in whales although this is well known in the cow (Hammond, 1927; Benesch and Wright, 

 1950), and is claimed for deer (Cheatum, 1949; Robinette, Gashweiler, Jones and Crane, 1955), 

 but disputed by Golley (1957). In any case his estimates were based ultimately on only seven pairs of 

 fin-whale ovaries and four pairs of blue-whale ovaries. 



Robins (1954) has recently claimed that in the humpback whale (Megaptera novaeangliae) it is 

 possible by morphological criteria to distinguish corpora lutea and corpora albicantia representing 

 ovulations from those representing pregnancies. Dempsey and Wislocki (1941) believed that in this 

 species restriction of the blood supply to the centre of the corpus luteum results in the formation of 

 a central cavity. Robins suggested that this applied only to the corpus luteum of pregnancy, which is 

 larger than the corpus luteum of ovulation (average 100-130 mm. and 80 mm. respectively), and claimed 

 that the presence of a central cavity or, in corpora albicantia, a central core was diagnostic of a corpus 

 of pregnancy. This hypothesis was based on a small number of ovaries and has not been confirmed. 

 A basic assumption, that the formation of a cavity is a result of the large size of the corpus luteum of 

 pregnancy, does not agree with observations on the incidence of cavities in fin- and blue-whale corpora 

 lutea (see below, p. 359). Van Lennep (1950) studied the histology of blue- and fin-whale corpora and 

 concluded that the corpora albicantia were persistent and that regression was completed in 3-4 years. 

 He was able to find no constant differences between corpora associated with ovulation or with 

 pregnancy, but made some suggestions about possible distinctions. Harrison (1949) and Sergeant 

 (Anon., 1955) made histological observations on Globicephala, but were unable to distinguish the two 

 types of corpora. Harrison stated that in this species only serial histological sections could be expected 

 to give a precise indication of the number of corpora albicantia, which regress to become invisible 

 macroscopically. Comrie and Adam (1938) made some observations on the ovaries of Pseudorca. 



