BY P. P. SANDES. 367 



Up to the year 1895 it will not be necessary to further review 

 the literature, except to state that Waldeyer held a view which 

 was a compromise between the two theories. He considered that 

 the epithelial element bore the greater part during the early 

 development of the corpus luteum, but that, in the later stages, 

 the theca folliculi had the greater share in its formation. 



The j'-ear 1896 marks a distinct advance in the mode of study 

 of this subject. Then there appeared from the pen of Sobotta a 

 paper based upon an exhaustive stud}' of the development of the 

 corpus luteum in the mouse. All modern methods of studying 

 this question must comply with the requirements that he has laid 

 down. His most important contention is that the corpus luteum 

 must be studied in all stages of its development, from its origin 

 onwards, and not only in its stage of full development. In this 

 research there have accordingly been chosen ovaries representing 

 all the chief stages of corpus luteum formation, the stage of the 

 development of the ovum and embryo being taken as a guide to 

 the time which has elapsed since fertilisation of the ovum. This 

 has the greatest advantages from a comparative point of view. 

 Sobotta's paper appears to have awakened fresh interest in this 

 question. He follows Bischoff's theory, and is supported by 

 Heape, Stratz, Honore, Belloy, van der Stricht, Bonnet, Bouin, 

 and van Beneden; whilst Nagel, Clark, Rabl, Kolliker, Doering, 

 Paladino, Biihler and His have come forward as upholders of von 

 Baer's theory. More extended criticism of these authors' views 

 will be given when necessary in the following chapters. 



Material and Methods. 

 Dasyurus viverrinus is a small marsupial, averaging when full- 

 grown about the size and weight of a half-grown rabbit. Once a 

 year it has a period of rut, during the months of May, June and 

 July, and only then does the congress of the sexes take place. 

 According to Hill, a varying period intervenes between coitus and 

 the fertilisation of the ovum, so that the period of gestation is 

 uncertain. It is probably about eight da3^s. After gestation is 

 completed, the embryo is transferred to the pouch. Six are 

 usually found there at a time. They remain attached to the 



