358 HISTOLOGY 



absorbed. It is replaced by gelatinous connective tissue which finally 

 contracts into a dense white fibrous nodule, and this scar is known as the 

 corpus albicans. Meanwhile the lutein cells undergo hyaline degeneration 

 and become resorbed. The surface of the ovary, which is smooth in child- 

 hood, becomes pitted and irregular with the increasing formation of these 

 corpora albicantia. 



Provided that pregnancy does not take place, the corpus luteum reaches 

 its maximum development in about two weeks after ovulation, and it be- 

 comes reduced to a scar in about two months. If pregnancy occurs, it 

 enlarges further and persists at the height of its development until the 

 fifth or sixth month. Its diameter is then 1.5-3.0 cm., and at the end of 

 pregnancy it is still quite large and yellow. If the corpus luteum is re- 

 moved, the ovum fails to become attached to the wall of the uterus. There 

 is both experimental and histoiogical evidence that it produces an internal 

 secretion which is probably received by the blood vessels invading it from 

 the theca. In order to distinguish between the corpus luteum of pregnancy 

 and that of unproductive ovulation, the former is called the true corpus 

 luteum; the latter is the corpus luteum spurium. 



Many follicles degenerate at various stages in their evolution without 

 discharging their ova. Leucocytes and cells from the stratum granu- 

 losum are said to invade the protoplasm of the oocytes, in which they dis- 

 integrate. The zona pellucida, which surrounds the oocyte, may become 

 conspicuously folded and persist for some time (Fig. 358). The basement 

 membrane of the stratum granulosum may also thicken and become con- 

 voluted. These degenerating or atretic follicles are finally reduced to 

 inconspicuous scars. After the menopause the degeneration of the oocytes 

 becomes general. 



Within the stroma of the cortex, interstitial cells are found, which re- 

 semble lutein cells but are smaller. They have been compared with the 

 interstitial cells of the testis, and are said to contain secretory granules. 

 Apparently they are derived from the thecae of atretic follicles (Cohn, 

 Arch. f. mikr. Anat, 1903, vol. 62, pp. 745-772; Allen, Amer. Journ. Anat., 

 1904, vol. 3, pp. 89-153). 



UTERINE TUBES. 



Each uterine tube is about 5 inches long and extends from its orifice 

 in the abdominal cavity to its outlet in the uterus. It is divided into the 

 fimbriated funnel or infundibulum; the ampulla or distensible outer two- 

 thirds, the lumen of which is about a quarter of an inch in diameter; the 

 isthmus or narrow inner third, not sharply separated from the ampulla; 

 and the uterine portion which extends across the musculature of the uterus 

 to the uterine orifice. The wall of the tube is composed of three layers, a 



