CORPORA ALBICANTIA, CORPORA ABERRANTIA AND CORPORA ATRETICA 373 



There are reasons for believing that in the fin whale there are about two unsuccessful ovulations 

 to one pregnancy (see pp. 459-63) and this appears also to be the case in Globicephala melaena 

 (Fisheries Research Board of Canada. Annual Report, 1953). 



This regression in diameter, in the second and most likely case, corresponds to a decrease in weight 

 from 500 to 5 g. (from Text-fig. 8), that is a percentage decrease of 99%. Because the density does 

 not change during regression this will equal the percentage decrease in volume. 



Unfortunately we do not have material directly representative of the contribution of the corpora 

 lutea of ovulation to the accumulating corpora albicantia, but as has been shown, the maximum 

 variation from the true percentage regression is unlikely to be more than 4-6%. In order to compare 

 material from different species we can only compare the size of the corpus luteum of pregnancy and 

 the size of the fully regressed corpora albicantia, derived from both corpora lutea of pregnancy and 

 corpora lutea of ovulation. The results might be expected to vary slightly according to the ratio of 



l/S 



2 

 < 



LARGEST 

 C.LJ? 



MEAN C.LP 



< 



MEAN C.L. \% 

 MEANC.LQ z 



■SMALLEST 

 C.L0. 



J 



I 2 3 



DIAM. OF REGRESSED C.A. (CMS.) 



Text-fig. 19. Mean diameters of corpus luteum of pregnancy and mean or modal diameters of fully regressed corpus albicans 

 (blue, fin, humpback, sperm and pilot whale). For the fin whale the estimated mean size of corpora lutea of pregnancy and 

 ovulation is shown (Fj), and method of estimating regressed size from initial diameter is indicated by dotted lines. 



ovulation and pregnancy corpora lutea although with small samples the experimental error will be 

 greater than this variation. In Table 4 and Text-fig. 19 the mean sizes of the corpus luteum of 

 pregnancy and the mean sizes of fully regressed corpora albicantia are given for five species of whales. 

 The data for the blue whale, humpback whale and sperm whale were obtained in the same way as the 

 fin whale data, though the material for the last two species is less abundant. The figures given for 

 Globicephala melaena are very approximate and are derived from the very few measurements given 

 by Harrison (1949). Nevertheless, the values for the percentage regression in diameter fall within the 

 range 82-6-84- l % • Mansfield (1958) gives measurements of 30 corpora lutea (mean diameter 24-4 mm.) 

 and 155 corpora albicantia (mode 6 mm.) of the Atlantic walrus, Odobenus r. rosmarus. These suggest 

 that the walrus corpus luteum regresses by about 75-5% in diameter, but the method of measurement 

 may be slightly different. For the two whale species for which the most observations are available 

 the percentage regression is identical. 



This table shows that on average corpora lutea from 5 to 13-75 cm. in average diameter, of very 

 different cetacean species, regress by a similar amount to a final size which is proportional to the 

 initial size. From this it follows that corpora lutea of varying sizes in a single species should regress 



