BY F. P. S ANDES. 365 



The collection of material and the obtaining of certain data 

 made use of in this paper were done by Mr. J. P. Hill, D.Sc, 

 F.L.8., Demonstrator of Biology in the University of Sydney, and 

 well known as an authority on the processes of generation in the 

 mar supial. To him the author tenders his sincere thanks for 

 suggesting the undertaking of this research and for placing at his 

 disposal a splendid series of ovaries in an excellent state of pre- 

 servation. 



The work was carried out during the year 1902 in the Anato- 

 mical Department of the University of Sydney, and to Professor 

 J. T. Wilson, its head, the author tenders his best thanks for 

 placing the resources of the Department at his disposal and for 

 his kindly interest throughout the progress of this investigation; 

 and he has also to thank Mr. Louis Schaefer, of the same Depart- 

 ment, for aid in producing the micro-photographs which illustrate 

 this paper. 



Short Review of the Literature. 



The literature of this subject is extensive, being scattered 

 through periodicals, reviews, text-books and essays, and extends 

 over three-quarters of a century of time, so that no exhaustive 

 review of it can be undertaken, apart from the fact that many of the 

 contributions in question are inaccessible in Australia. For a 

 more extended criticism of different authors' views, and for an 

 excellent bibliography up to the year 1895, the reader is referred 

 to Sobotta's paper " Uber die Bildung des Corpus Luteum bei 

 der Maus " in the Archiv filr Mikroscopische Anatomie, Bd. 47, 

 1896, and to contributions mentioned therein; also to an article 

 by the same author in Merkel and Bonnet's Ergebnisse, Bd. 8, 

 1898; and to J. G. Clark's article in the Archiv fiir Anatomie 

 und Physiologie, 1898. It will be necessary to mention here only 

 those points which enable the reader to follow the discussion. 



In the year 1827 appeared a treatise by von Baer on the origin 

 of the mammalian ovum. He described the ovum in the interior 

 of the Graafian follicle, and recognised the fact of its escape by 

 rupture. He described also the wall of the Graafian follicle, com- 



