CORPORA ALBICANTIA, CORPORA ABERRANTIA AND CORPORA ATRETICA 383 



The mean diameter of those measured was 1-27 ±0-14 cm., but the modal diameter is 075 cm. 

 and the true mean diameter is probably less than 1 cm. 



All stages in the formation of these bodies have been observed, from a relatively large follicle 

 (maximum 3-5 cm.) with slightly folded walls and a bright orange lining, through similar follicle stages, 

 becoming more and more collapsed, and finally to small (4 mm.) stellate bodies or thin compressed 

 orange streaks (Text-fig. 23 d-h). These undoubted chronological stages confirm that these bodies are 

 corpora atretica. They have, therefore, been ignored in making the routine counts of corpora for 

 purposes of age-determination (p. 466). There are also collagenous unpigmented corpora atretica in 

 which the original follicle wall can be identified (Text-fig. 23 i). 



The histology of one such pigmented body is illustrated in PI. VII, figs. 5, 7. This shows it to be 



composed of tissue heavily laden with lipoid globules, but with very little collagenous material. 



It also shows the folding of the original follicle wall. These corpora atretica appear to be homologous 



with the 'corps lipoides' or 'formations spongiocytaires ' of the human ovary described by 



Dubreuil and Riviere (1947, p. 83 and fig. 26 I). The third kind of atypical corpus of the rhesus 



monkey described by Corner, Bartelmetz and Hartman (1936) also appears to be in this category. 



It is largely composed of clear lipid-filled cells believed to be derived from the theca interna, 



but there is also a distinct zone of darker cells which appear to be granulosa cells. Brambell (1956, 



p. 501) described the corpora lutea atretica found in various mammals and states that, according to 



the majority of authors, these corpora originate by hypertrophy and hyperplasia of the cells of the 



theca interna after degeneration of the membrana granulosa. Owing to the small amount of whale 



material which has been examined histologically, it is not possible to say definitely whether whale 



corpora atretica are composed mainly of transformed theca interna cells or are developed from the 



granulosa layer. 



Conclusions 



Old, non-functional corpora lutea are termed corpora albicantia although the majority are still 

 pigmented. There is no significant difference in the mean size of corpora albicantia of pregnant, 

 non-pregnant and lactating females, which have a mean diameter of 2-5 cm. and a mean weight of 

 about 10 g. The relation between weight and diameter for corpora albicantia is the same as that for 

 corpora lutea and there is no significant alteration in density as a result of the changes in composition, 

 appearance, and histology. 



The morphological types of corpora albicantia correspond to the types of corpora lutea and in 

 particular the incidence of vesicular or radiate corpora albicantia is not significantly different from 

 the proportion of vesicular corpora lutea. This confirms that the incidence of vesicular corpora lutea 

 of ovulation is not appreciably different from the incidence of vesicular corpora lutea of pregnancy. 



Three age-groups of corpora albicantia have been identified on the basis of anatomical and histo- 

 logical changes. 'Young' corpora albicantia have a mean diameter of 4-01 cm. and a weight of 41 g.; 

 the values for 'medium' corpora albicantia are 2-94 cm. and 15 g.; and for 'old' corpora 2-01 cm. 

 and 5 g. The latter group has been shown to represent the final stage of regression when the corpus 

 largely consists of unpigmented collagen. 



Evidence which is considered to be conclusive has been presented showing that the corpora persist 

 throughout the life of the individual. It appears that corpora lutea regress by a constant proportion 

 of their initial size to a final size which is directly related to the initial size. Only the remnants of those 

 corpora lutea originally under 3 cm. in diameter are likely to be missed in the routine examination of 

 5-mm. slices. This means that no more than 1 % of ovulations are unrepresented by corpora albicantia 

 large enough to be recorded in the conditions of the routine examination, and for practical purposes 

 of employing corpora counts for age-determinations this may be regarded as negligible. 



