366 DISCOVERY REPORTS 



production of pregnancy corpora lutea in the life of the whale, if there were any important difference 

 such as Robins (1954) or Van Lennep (1950) suggest, this would affect the proportion of 'radiate' 

 corpora albicantia and it might be expected to be significantly higher (Van Lennep) or lower 

 (Robins) than the incidence of vesicular corpora lutea of pregnancy. 



Age groups of normal corpora albicantia 

 Three groups of corpora albicantia have been identified in fin-whale ovaries on the basis of gross 

 anatomical and histological changes. Since they have an important bearing on age determination in 

 whales they must now be described in some detail. The corpora have been examined macroscopically, 





mm 



W 



lcm. 



i — 1 — 1 — 1 — 1 

 5 mm. 



Text-fig. 13. A, typical 'young' corpus albicans; B, typical 'medium' corpus albicans; C, 'old' corpus albicans which 

 still has a conspicuous pigmented layer. (Large-scale drawings are from thick sections cleared in xylol and methyl salicylate.) 



when fresh or after fixation in formalin ; by examination of 5 mm. thick slices cleared in xylol and 

 methyl salicylate; and by histological examination of material fixed by various techniques. The 

 material for histological examination has been fixed in formalin, Bouin's fluid, and Zenker-formol 

 (Helly) and part of the latter material was post-osmicated with 2% osmium tetroxide to demonstrate 

 the distribution of lipoids. This material has been embedded and sectioned by the standard paraffin 

 wax technique and stained with Heidenhain's Iron Haematoxylin and Eosin, Delafield's Haematoxylin 

 and Eosin, Mallory's trichrome, Masson's trichrome, and Van Gieson. 



The routine macroscopic examinations and counts are made by eye on formalin-fixed material. 



