78 Proceedings of the Royal Irish Academy. 



PI. V, fig. 5, GT). These cells are probably derived from the original theca 

 interna or from endothelial elements, as is indicated by our knowledge of 

 lower animals, and by the figures of Novak for the human Graafian follicle, 

 just before rupture. 



If one studies such Da Fano sections more closely, one gets the impi-ession 

 of the presence of still another kind of cell in the human corpus luteum. 

 These cells are not much smaller than the lutein and stellate cells, and are 

 characterized by the fact that they are very elongate and that their nuclei 

 often take the green stain instead of the safraniu (which stains the nuclei of 

 stellate cells). This difference may be due to some slight change in the 

 ordinary stellate cells, and I do not wish to stress tlie staining behaviour 

 of such enigmatic cells. 



In the human corpus luteum of menstruation we seem to have at least 

 five sorts of cells: — (a) luteal cells, {h) stellate cells, {c) endothelial cells, 

 [d] elongate or spindle cells, and finally the cells of the theca externa columns 

 and lamellae. As before mentioned, Corner has noted two sorts of cells, other 

 than the luteal and theca externa cells. His additional cells, type 1, are 

 probably category (rf), above, and his additional cells, type 2, are almost 

 certainly category (5), above. In Oruithorhynchus the corpus luteum seems 

 to contain three types of cells, derived simply from the three elements of the 

 Graafian follicle. No such stellate cells could be found in the platypus. 



We may now proceed to a more minute examination of each type of human 

 cell, and endeavour to throw some light on the origin and true nature of each. 



(a) The Luteal Cell. 



The luteal cells of the human corpus luteum are large elements sometimes 

 as much as 30 w. in diameter. They vary considerably in size from the 

 smallest, which are situated in nests [N) near the theca externa ('/') in 

 PI. III. fig. 'd, to the largest, which are found towards the interior of the 

 corpus luteum. These nests of unchanged cells have a characteristically 

 dense small Golgi apparatus, which grows larger and looser in the bigger 

 luteal cells, deeper in towards the centre of the organ. In PI. Ill, fig. '^, 

 there are three nests of almost unchanged follicle epithelial cells at N: 

 these nests of small cells pass imperceptibly into the larger, more glandular 

 luteal cells, and are probably of the same nature. There is no evidence that 

 these cells are theca interna elements, even though the nests do abut against 

 the theca externa tunic. In PI. Ill, fig. 2, the characteristic arrangement of 

 luteal (i) and stellate cells {AS) is shown : surprisingly few interstitial or 

 cicatricial elements were present in this corpus luteum especially in view of 



