388 THE CORPUS LUTEUM OF DASVI'JirS, 



Next, it is interesting to note that the discrepancy of authors' 

 views depends to some extent on the size of the animal studied. 

 His, for instance, said at Kiel in 1898, that in man and in larger 

 mammals, the formation of corpora lutea from the theca interna 

 was absolutely indisputable. Biihler, too, at Pavia in 1900, said 

 that it was certainly not an accidental circumstance that the 

 accounts of the origin of the corpus luteum should be so diametri- 

 cally opposed in the smaller as compared with the larger mammals. 

 Sobotta (Tubingen, 1899) denies that the size of the animal has 

 anj^thing to do with the question, and upon the grounds of com- 

 parative anatom}' there would appear to be no reason wh}^ the 

 origin of such a constantly occurring structure as the corpus 

 luteum should be so radically altered. If it is so, in what animals 

 of the mammalian order does the transition in mode of formation 

 take place, or where do the transitional forms of corpus luteum 

 appear ? One is justified in supposing that the mode of formation 

 of the corpus luteum is uniform throughout the mammalian order, 

 though it may be obscured by accidental circumstances, so that, 

 what holds good in Dasyurus — a marsupial — would probabl}' 

 hold good in the rabbit, mouse and guinea pig, and probably also 

 in larger animals, as man and the swine. 



But what are these accidental circumstances'? It has been 

 pointed out by various authors that the theca folliculi of most ani- 

 mals is composed of an outer fibrous theca externa and an inner 

 theca interna, whose cells are more or less polygonal and filled with 

 granules of the so-called "lutein" substance, and have between 

 them a certain amount of intercellular fibrous tissue. There is 

 in fact a definite specialisation of the theca folliculi into two 

 layers. jSTow, many authors attribute the origin of the charac- 

 teristic cells of the corpus luteum to the specialised theca interna, 

 some on altogether insufificient grounds. Thus His (at Kiel, 1898) 

 says that the structure of the theca interna folliculi is identical 

 with that of the young corpus luteum. Nagel uses the same 

 argument, but that is no proof that one originates from the other. 

 His also says that the transition from one to the other can be 

 traced step by step. Does he refer to one corpus luteum, or to 



