364 DISCOVERY REPORTS 



corpus luteum, routine measurements of only two diameters have been practicable during slicing. It 

 is assumed that since the corpora appear to be randomly oriented, this does not introduce any important 

 degree of error into the results. The corpora were placed in three morphological classes (independent 

 of size) to be described below. These are termed ' young ', ' medium ' and ' old ' corpora albicantia, 

 and are believed to represent three definite stages in the regression of the corpus luteum. The evidence 

 for this view is presented below. 



The mean diameter of 3181 corpora albicantia from pregnant females is 2'56±o-o3 cm., and for 

 884 from non-pregnant females it is 2-52±o-o7cm. From this season there are only 89 corpora 

 albicantia from females known to be lactating, and the mean size is 2-5 ±0-9 cm. These differences 

 are not significant, and this mean diameter corresponds to a weight of about 10 g. (see Text-fig. 8). 

 In Text-fig. 1 1 the percentage size frequency distribution of these corpora albicantia from pregnant 



S 10 



DIAMETER IN CMS 



Text-fig. 11. Frequency distributions of corpora albicantia sizes. 



-• pregnant; O O non-pregnant. 



and non-pregnant females is presented. They range in size from 7 to 80 mm. corresponding to a 

 variation in weight from less than 0-4 g. to about 300 g. It will be noticed that a proportion of non- 

 pregnant females ('resting females') have a large corpus albicans about 4-75 cm. in diameter, whereas 

 the curve for pregnant females lacks this subsidiary peak. The modal diameter for both groups is 

 2-25 cm. Only 34 corpora albicantia have been weighed, mostly in the size range 4-7 cm., because it 

 is difficult to isolate corpora albicantia for weighing, embedded as they are in the ovarian stroma. The 

 results have been incorporated in Text-fig. 8 where the mean weights for corpora albicantia 2-3 cm., 

 3-4 cm., 4-5 cm., etc. in diameter are plotted on a double logarithmic graph. These points fall along 

 the regression line for corpora lutea, so there has been no observable alteration in density cor- 

 responding to the change from corpus luteum to corpus albicans. Corpora albicantia sizes will be 

 discussed more fully when the different morphological classes have been described. 



Morphological types 



In Text-fig. 12 and PI. V, fig. 1 the various morphological types of corpora albicantia are illustrated and 

 if they are compared with the corpora lutea illustrated in Text-figs. 5 and 10 the similarity in their archi- 

 tecture is readily apparent. In general the white connective tissue septa of the corpus albicans are much 

 thicker than those in the corpus luteum and the lobes of brown hyaline collagen, representing the 



