CHANGES IN THE OVARY 147 



on growing usually for only a short time and then degenerates, so 

 that, in the case of the human female, two months after ovulation 

 it is reduced to the condition of an insignificant cicatrix. Miller 1 

 found that in man the beginning of menstruation coincided with 

 the degeneration of the corpus luteum. In polyrestrous animals 

 which ovulate spontaneously the organ is in process of reduction 

 at about the time of the next " heat " period, but two corpora 

 lutea of different ages have been observed in the same ovary. Thus 

 Corner 2 finds that in the sow there is, during the sexual season, 

 a regular overlapping in the duration of these structures, and at 

 any oestrus after the second there are in the ovaries corpora lutea 

 in an advanced stage of degeneration, probably six weeks old, and 

 others, about three weeks old, in a much less retrogressive condition. 

 In Mammals which experience pseudo-pregnancy the corpus luteum 

 under that condition may persist for a considerable time, which 

 is as long, or nearly as long, as if pregnancy had occurred, but 

 Hammond has shown that in the rabbit, in which pseudo-pregnancy 

 only occurs under experimental conditions (see p. 101), the corpora 

 lutea in the later part of gestation are larger than those of pseudo- 

 pregnancy. If conception succeeds ovulation, the corpus luteum con- 

 tinues to increase in size until almost the middle of pregnancy, and in 

 the human female attains to a diameter of nearly an inch in length. 



The large size of the completely developed corpus luteum is the 

 more remarkable in that it results to so large an extent from the 

 simple hypertrophy of certain of its constituent cells. The wonderful 

 property which these cells possess of enlarging within a very short 

 time of ovulation is seemingly without a parallel in the physiology 

 of the Vertebrata, and it becomes additionally interesting in view of 

 the almost certain fact that the cells, from which the luteal cells 

 develop, are derived, like the ova, from the original germinal 

 epithelium. 



During the later part of pregnancy the corpus luteum becomes 

 reduced in size, the luteal cells degenerating, losing their . yellow 

 colour,, and eventually (at least in some cases) appearing to become 

 transformed into cells resembling, if not identical with, the ovarian 

 interstitial cells referred to above (see p. 114). 3 At the end of 

 pregnancy the human corpus luteum has a diameter not exceeding 

 half an inch in length. In some animals at any rate (rats, etc. ; see 

 p. 149) it may persist during the beginning of the lactation period. 



1 Miller, "Corpus Luteum, Menstruation, und Graviditat," Arch. f. 

 vol. ci., 1914. 



2 Corner, " Cyclic Changes in the Ovaries and Uterus of the Sow," Carnegie 

 Institution Publication (Contributions to Embryology, No. 64), 1921. 



3 Schafer, Essentials of Histology, 7th Edition, London, 1907. The similarity 

 between the luteal and interstitial cells has also been remarked upon by Allen, 

 Joe. n't. 



