. 30 20 /^^__ IO 1 1 1 1 1 1 1 1 9 10 11 u 13 CL. DIAMETER IN CMS. 9 10 II \2 CL DIAMETER IN CMS Text-fig. 9. a, Relation between cavity diameter and corpus luteum diameter, b, Relation between corpus luteum size and the incidence of cavities. The appearance of fin-whale corpora lutea of the vesicular type suggests that they are usually formed in this way. In most corpora with large cavities (Text-fig. 5 h-k) the stigma is inconspicuous and there is no eversion of luteal tissue to form a corona. This suggests that the aperture became closed again after ovulation and remained closed. The corpus
. 30 20 /^^__ IO 1 1 1 1 1 1 1 1 9 10 11 u 13 CL. DIAMETER IN CMS. 9 10 II \2 CL DIAMETER IN CMS Text-fig. 9. a, Relation between cavity diameter and corpus luteum diameter, b, Relation between corpus luteum size and the incidence of cavities. The appearance of fin-whale corpora lutea of the vesicular type suggests that they are usually formed in this way. In most corpora with large cavities (Text-fig. 5 h-k) the stigma is inconspicuous and there is no eversion of luteal tissue to form a corona. This suggests that the aperture became closed again after ovulation and remained closed. The corpus illustrated in Text-fig. $k has a small stigma, but the corpus has a distended appearance and the luteal tissue has obviously been subjected to pressure from inside, presumably by continued secretion of fluid. The most uncommon type of corpus (Text- fig. 5 /) has an opening and a conspicuous corona. It immediately suggests that the aperture closed after ovulation, but that the internal fluid pressure later forced it open when the corpus luteum had almost attained its definitive size and form. There is a relation between the size of the corpus and the size of its cavity (Text-fig. ga). For 107 fin-whale corpora for which the cavity size is known the mean size of the cavity increases from i-8 cm. at a corpus size of 7-8 cm., to 4-1 cm. at a corpus size of 14-15 cm. There is also a relationship between the size of the corpus luteum and the prevalence of the vesicular type. For 701 corpora lutea, 120 of which have cavities, the percentage of vesicular corpora in suc- cessive size groups increases from about 10% at a corpus size of 6-7 cm. to about 20% in corpora above 13 cm. in diameter (Text-fig. gb). In other words the larger corpora show a greater tendency to have cavities. Extrapolation suggests that corpora below 3-4 cm., forming from ruptured follicles, would not be vesicular. The limited material available supports this. In Text-fig. 10 a number of small accessory corpora l
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