190 FRANCIS H. A. MARSHALL. 
The first really systematic effort to deal with the question 
was made by Sobotta, whose earliest paper on the subject was 
published in the ‘ Anatomischer Anzeiger’ in 1895. In the 
following year the complete paper was issued. These papers 
describe an investigation on the development of the corpus 
luteum in the mouse, in which a large series of stages was 
examined, each of them being collected according to a definite 
plan, the animals being killed at known intervals after the 
occurrence of coition, in reference to which the period of 
ovulation had been previously determined. Sobotta’s in- 
vestigation resulted in confirming Bischoff’s view that the 
lutein cells are the much hypertrophied epithelial cells of the 
undischarged follicle, the connective-tissue element which 
forms an anastomosis among the lutein cells being derived 
from the inner layer of the theca. The theca externa is 
described as taking no share in the ingrowth, while the theca 
interna is stated to become entirely used up in the formation 
of the interepithelial network. The hypertrophy of the 
epithelial cells is described as being of the nature of a 
simple enlargement, unaccompanied by cell division. The 
cavity of the follicle is said to become eventually filled up by 
a central plug of connective tissue. 
The conclusions reached by Sobotta regarding the for- 
mation of the corpus luteum were subsequently corroborated 
by him in an investigation on the corpus luteum of the rabbit, 
the stages of development being also obtained by killing the 
animals at stated intervals after coition. 
In 1898 Stratz published descriptions of stages in the for- 
mation of the corpus luteum of Tarsius, Tupaia, and 
Sorex; and these agree in all essential particulars with the 
accounts given by Sobotta. 
The development of the rabbit’s corpus luteum was also 
studied by Honoré, who adopted the same method as that 
employed by Sobotta. According to Honoré the inter- 
epithelial proliferation of connective tissue is derived in part 
from the theca externa, and not exclusively from the inner 
theca, as supposed by Sobotta; while the theca interna is 
