ORIGIN OF THE CORPUS LUTEUM 121 



the necessity of transformation or regression of the specialized 

 theca cells into fibroblasts, as described by Sobotta. So far as is 

 known to me, no subsequent investigator has confirmed the view 

 of Stratz, all others being agreed that the theca interna consists 

 of a distinct layer of highly specialized cells derived from the 

 mesenchymatous elements of the ovarian stroma, and containing 

 a network of blood-vessels, supported by cells and fibrils of con- 

 nective tissue. 



A third theory as to the fate of the theca interna is proposed 

 in the important papers of 0. Van der Stricht, of which the first 

 appeared in 1901. The study was carried out upon the ovaries 

 of large numbers of European bats, chiefly Vesperugo noctula. 

 As with the two previously cited investigations, the animals were 

 collected primarily for the study of the ova and the early embryos 

 of the species used, and the series is therefore accurately con- 

 trolled by the condition of the ova. Van der Stricht demon- 

 strates beyond doubt that in these species the granulosa layer 

 persists in situ after rupture of the follicle, and that its cells en- 

 large, acquire granules of lipoids staining black with osmium 

 tetroxide, and finally become the typical lutein cells. Contrary 

 to Sobotta, he thinks that mitotic division may occasionally occur 

 in these cells, so that the filling of the follicular cavity is brought 

 about by a slight increase in their number as well as by the vast 

 increase in their individual bulk. The connective tissue of the 

 corpus luteum arises chiefly as Sobotta described it in the mouse. 

 After rupture of the follicle the membrana propria disappears, 

 and fibroblasts invade the metamorphosing granulosa layer. Van 

 der Stricht thinks that these are the spindle-cells of the theca 

 interna or their descendants. Of the distinctive cells of the 

 theca, some seem to disappear, but others remain, chiefly about 

 the periphery of the new corpus luteum, or enter a short distance 

 into the granulosa, and here they remain almost in their original 

 condition. After a few days, however, when the deposition of 

 fatty droplets in the granulosa cells has progressed, the two types 

 of cells so closely resemble each other that Van der Stricht could 

 no longer distinguish them in his Flemming-fixed tissue. He 

 believes, in fact, that they have become identical, and therefore 



