244 DISCOVERY REPORTS 



luteum in the ovaries, is referred to as the corpus luteum a, and the older corpora lutea 

 in various stages of resorption are designated corpora lutea b. The corpora lutea a of 

 pregnancy become early corpora lutea b at parturition, but the corpora lutea a of sterile 

 ovulation degenerate gradually into corpora lutea b with no definite line of demarcation. 

 Old corpora lutea b are, strictly, corpora albicantia. The length, breadth and thickness 

 of the corpora lutea were measured and the average of these three measurements is 

 taken as the mean diameter in this report. 



Fig. 69 is a scatter diagram of the mean diameter of corpora lutea a plotted against 

 lengths of the corresponding foetus. In those cases where data were available the largest 



Foetus Length in metres 



Fig. 69. Sei whale. Females. Mean diameter of corpora lutea, and foetus lengths. 



co-existing corpora lutea b have also been plotted, and two isolated points give some 

 indication of the size of the corpus luteum at ovulation and during lactation. It will be 

 noted that the size of the corpora lutea a increases slightly but steadily from ovulation 

 until the foetus reaches a length of about 4 m., beyond which foetus length data are 

 lacking. During lactation, however, the size of the corpus luteum has shrunk rapidly, 

 so that it is no larger than the persisting corpora lutea b of the previous oestrous cycle 

 and pregnancy. The mean diameter of the corpus luteum a for foetus lengths from 

 I to 4-5 m. averages 8-55 cm. with a maximum of ii-i cm. and a minimum of 5-1 cm. 

 The only recorded corpus luteum a of ovulation measures 7-3 cm. in mean diameter. 



