GrATENBY — Notes on the Human Ovary. 71 



Platypus. In this form there can be no doubt as to the origin and manner of 

 metamorphosis of the various histological elements of the corpus luteum. 



Just as in the higher mammals, there are three layers concerned, the 

 membrana granulosa or follicle epithelium, the theca interna, and the theca 

 externa. The lutein cells come from the follicle epithelium alone, and are 

 always, in the adult corpus luteum, clearly distinguishable from those of the 

 theca interna: therefore the question of the origin of the lutein cells from 

 element other than follicular epithelium, cannot be entertained. In the 

 Platypus, tlie theca interna cells form or aid in forming lymph channels, 

 blood-vessels, separating tissue, inter-cellular spaces, and their purpose 

 throughout is that of enabling the glandular products of the luteal cells to 

 be carried away, and for the lymph and blood-vessels to penetrate every 

 corner and element of the corpus luteum. The them interna alls at no time 

 approach the follicle epithelial {granulosa) cells in iize. We can thus speak 

 dogmatically on this question of the origin of the lutein cells, in so far as the 

 Platypus can be taken as representing the mammalian type. 



In the Platypus, up to a late stage, there is a fairly well-marked and 

 constant difference between the cells of the theca interna and those of the 

 theca externa. In the fully formed corpus luteum one does find places 

 where it is not at all easy to discriminate between these two categories of 

 cells, but in certainly the majority of cases which Professor J. P. Hill and I 

 examined, the differentiation was marked. In ( )rnithorhynchus, the theca 

 externa fuuctious at once as a sheath for the confinement of the corpus 

 luteum, and as a base for the ingrowth of the connective tissue trabeeulae 

 carrying in both large blood- and lymph- vessels, and the elements of the 

 theca externa which function for the further opening up of the glandular 

 material. 



In our material of Ornithorhynchus we discovered elongate mitochondrial 

 elements within the luteal cells, probably corresponding to the luteal granules 

 of higher forms. This is a matter which, to my mind, still requires a good 

 deal of careful microscopical work, especially from the comparative point of 

 view. The work carried out on Ornithorhynchus should serve as a basis for 

 future researches on the comparative histology of the corpus luteum of 

 mammals and Sauropsida in general. 



Apart from the description of the formation of the corpus luteum of the 

 bat by Van der Stricht, and of Ornithorhynchus by J. P. Hill and the writer, 

 one of the most thorough descriptions of the mammalian corpus is that by 

 the American worker, George W. Corner. This paper was published in 1915, 

 and Corner has attempted to describe the minute cytology of the lutein cells. 

 His technique is somewhat inadequate — formalin fixation followed by 



