THE CORPUS LUTEUM 361 



of 8-28 ±0-82 cm. might be expected to include a slightly lower proportion with cavities than pregnancy- 

 corpora. Of fifteen corpora lutea of ovulation examined in 1953/54 and 1955/56, only one (67%) 

 possessed a central cavity, but this is too small a sample to give a significant result. 



Accessory corpora lutea 

 Of 760 corpora lutea examined, 28 or 37% were accessory corpora ranging from 0-4 to 8-5 cm. in 

 diameter, the mean diameter being 3-88±o-8 cm. and the weight about 45 g. It is likely that many 

 more small accessory corpora lutea form, but corpora less than 7 mm. in diameter are usually missed 

 in the routine examinations; one accessory corpus 1 mm. in diameter has, however, been seen in 

 histological preparations. The material is rather too sparse to allow firm conclusions to be drawn, but 

 accessory corpora lutea of ovulation appear to occur as frequently as accessory corpora lutea of 

 pregnancy. 



Text-fig. 10. Morphological variation in accessory corpora lutea. See text. 



They fall into two main groups; the larger, having developed from ruptured follicles, show a 

 stigma and small corona, but the smaller are formed from unruptured follicles. 



A female fin whale 73 ft. in length taken on 8 February 1954 had recently ovulated, but no products 

 of conception were seen in the uterus. There were three small corpora lutea in one ovary, one of which, 

 23-5 mm. in diameter, had ovulated, and two measuring 13 and 15 mm. (Text-fig. log, h) had developed 

 from unruptured follicles. The appearance of the luteal cells is similar in all three. They are derived 

 from the membrana granulosa because theca interna cells can be seen at the periphery of the gland 



5-2 



