CORPORA ALBICANTIA, CORPORA ABERRANTIA AND CORPORA ATRETICA 367 



' Young corpora ' 



This group includes those corpora which have undergone least regression; some are very recent 

 bodies, parts of which still appear macroscopically like the corpora lutea from which they have 

 developed. 



The size range of 628 corpora of this type is 1-5-7-5 cm -» mean diameter 4-01 ±0-07 cm., cor- 

 responding to a weight of about 41 g. The great range means that size cannot be used as a distinguishing 

 character. Usually, but not invariably, corpora of this type project from the surface of the ovary after 

 the fashion of corpora lutea. 



The macroscopic appearance of a typical 'young' corpus albicans is shown in Text-fig. 13 A and 

 PI. V, fig. 1. There is a conspicuous central core of white connective tissue, but the lobes of brown 

 collagenous tissue are extensive and the connective tissue septa are rather inconspicuous. It appears 

 that when the corpus luteum regresses the blood supply to the luteal tissue is cut off and hyaline 

 degeneration of this tissue then occurs. As the luteal cells are replaced the corpus luteum shrinks in 

 size and the network of connective tissue strands condenses and becomes more conspicuous. 



In the 'young' corpus albicans, vascular reinvasion of the pigmented collagenous tissue has begun, 

 and a number of spiral arteries can be seen, but it has not progressed very far (Text-fig. 13 A and 

 PI. V, fig. 2). The white connective tissue core and septa, representing the original cavity of the 

 newly ruptured follicle, are avascular and remain so throughout subsequent regression. 



Examination of cleared thick sections shows the yellow pigment granules to be distributed evenly 

 throughout the hyaline collagen. Sometimes, in very recent corpora, they are very densely arranged 

 so as to give the corpus a shining golden-yellow appearance. Thin sections stained for lipoids (Zenker- 

 formol fixed, and post-osmicated) show the distribution of pigment very clearly (PI. V, figs. 2, 3, 5, 6). 



Rossman (1942) has shown that the pigments of the corpus luteum and the corpus albicans have 

 little in common. He states that it is generally held that the colour of the corpus luteum is due to a 

 carotenoid dissolved in lipin droplets (see PI. VI, figs. 3-5) so that the colour largely disappears on 

 treatment with fat solvents. The pigment of whale corpora albicantia does not dissolve in fat 

 solvents (xylol, methyl salicylate), which suggests that it is similar to the 'luteolipin' described by 

 Rossman in the corpora of the rhesus monkey, Macaca rhesus. 



' Medium ' corpora 



These represent a later stage of regression and have usually sunk into the general stroma of the 

 ovarian cortex so that they do not project very far. They retain a characteristic stigma and corona at 

 the surface. They are smaller than the more recent corpora with a mean diameter, for a sample of 

 1098 of 2-94±o-045 cm., corresponding to a weight of about 15 g. The size ranges from 0-7 to 5-5 cm. 

 and this character is not used for identification. 



The macroscopic appearance of a typical ' medium ' corpus albicans is shown in Text-fig. 13 B. The 

 central white connective tissue core does not show further enlargement from the ' young ' condition, 

 but as the corpus shrinks in volume the septa become rather more conspicuous. The most charac- 

 teristic macroscopic change is a reduction in the amount of brown hyaline tissue. In thick cleared 

 sections vascularization can be seen to have progressed much further, and there are large thick- 

 walled vessels at the periphery of the corpus. This tangle of sclerotic blood vessels gives to the corpus 

 a thick white connective tissue capsule. Material stained for lipoids shows that there is a clear 

 unpigmented zone of collagen in the vicinity of the blood vessels (PI. V, fig. 2), and demonstrates that 

 phagocytic activity proceeds inwards from the vascularized outer trabeculae towards the inner avascular 

 connective tissue septa. As the phagocytes take up the pigment and move inwards they concentrate the 



