CHANGES IN THE OVARY 145 



theory of . the mode of formation of the corpus luteum may be 

 summarised as follows: The luteal cells represent the epithelial 

 cells of the undischarged Graafian follicle. These, after rupture, 

 undergo a great hypertrophy, which may be accompanied in the 

 earlier stages by mitotic division, but only to a relatively slight 

 extent {Ovis, Vespe-mgo, etc.). ' Meanwhile the thickness of the wall 

 of the discharged follicle is further increased by an -ingrowth of 

 connective tissue, which eventually forms an anastomosis of cells, 

 generally fusiform in shape, between the hypertrophying follicular 

 epithelial cells. This connective tissue ingrowth is either derived 

 from the theca interna alone {Mus, Cavia, Tarsius, Tupaia, Sorex, 

 Dasyunis, Vesperugo, etc.), or it may arise from both the theca 

 interna and the theca externa (Zepus, Ovis, Spermophilus). The 

 theca interna may become entirely spent in this process {Mus, Cavia, 

 Tarsius, Tupaia, Sorex, Ovis, Dasyurus), or certain strands of this 

 layer may still remain and line the outside edge of the follicle after 

 it has become transformed into a fully developed corpus luteum 

 (Zepus, Spermophilus, Vesperugo). In some animals the interstitial 

 cells of the theca interna may develop into luteal cells in just 

 the same manner as the follicular epithelial cells ( Vesperugo, etc.). 

 The cavity of the discharged follicle becomes filled in eventually 

 by the further ingrowth of connective tissue, which forms a central 

 plug. 



The changes undergone by the discharged follicle have also been 

 studied in certain of the lower Vertebrates. Giacomini,i who has 

 investigated the subject in birds, amphibians, and, more particularly, 

 Elasmobranch fishes, describes an hypertrophy of the follicular 

 epithelium consequent upon ovulation. The discharged follicle of 

 Myliohatis is described and figured as a glandular body in which 

 the enlarged epithelium is penetrated by an extensive ingrowth of 

 connective tissue and blood-vessels. Wallace^ gives a somewhat 

 similar account of the spent follicles in the fishes Zoarces and Spinax. 

 In the latter especially there is a pronounced hypertrophic enlarge- 

 ment of the follicle-cells, associated with thecal ingrowths arrayed 

 in a radial manner. Lucien^ has described corpora lutea_ in the 

 reptiles Anguis and Seps, in which there is a simple hypertrophy 

 of the follicular epithelium unaccompanied by mitotic division. 

 Similar structures in reptiles have als6 been observed by Mingazzini,* 



' Giacomipi, " Contributo all' Istologia dell' Ovario dei Selaci," Ricerca Lab. 

 di Anat. Normale della Roy. Univ. di Roma, vol. v., 1896. 



2 "Wallace (W.), "Observations on Ovarian Ova, etc.," Quar. Jour. Hicr. 

 Science, vol. xlvii., 1903. 



•'' Lucien, " Note pr61iminaire sur les premieres Phases de la Formation des 

 Corps Jaune chez certains Reptiles," C. R. de Soo. de Biol., vol. Iv., 1903. 



* Mingazzini, "Corpi Lutei verie falsi da Rettili," Ricerca Lab. di Awxt. 

 Nwmale della Roy. Univ. di Roma, vol. iii., 1893. 



