320 
PROFESSOR ARTHUR ROBINSON ON 
differ in details as to the mode of its formation ; whilst Waldeyer (42) and 
Nagel (28) believe that it is formed by the follicle cells, and Nagel says that 
it is structureless, non-nucleated, and is similar at first to the oolemma. 
In the ferret its reaction to stains is not the same as the reaction of the oolemma, 
and when the follicular epithelium is detached from the internal theca by the action 
of the fixative reagents, the membrana external separates into two layers (figs. 58, 
60, PI. X). The inner of the two layers is connected with the outer ends of the 
follicle cells, and is possibly formed by them, in the same way that the external 
limiting membrane of the central nervous system is formed by the outer ends of the 
neuroglial cells. The outer layer is connected with the innermost flattened- cells of 
the internal theca, and it reacts like other connective-tissue structures to connective- 
tissue stains. 
The external limiting membrane is present at a very early stage of the life-history 
of the follicle, being formed when the follicular epithelium is a single layer of cubical 
cells. Its function is unknown, but its constant presence indicates utility, and it 
possibly regulates the passage of different materials in opposite directions to and 
from the follicle. 
Membrana limitans interna. 
So far as I am aware, the only observers who have noted the presence of an 
internal limiting membrane in ovarian follicles are Bourn and Ancel (4), who describe 
it as occurring in the ovarian follicles of the bitch. One of Longley’s figures of 
part of an ovarian follicle of a cat (20) suggests that it is present in that animal also, 
and one of Russo’s photographs (34) indicates that it may be present in the mature 
follicles of the rabbit. 
According to Bouin and Ancel’s account of the internal limiting membrane in 
the bitch, it is formed, in that animal, by the flattening out of the internal cells of 
the granulosa, which are transformed into a series of closely applied lamellse. They 
also state that when it is definitely established it reacts to stains in the same 
manner as the external limiting membrane, and they conclude, therefore, that some 
external membranes may also be of epithelial origin. They do not discuss the 
function of the internal membrane, but they say that as the corpus luteum is formed 
the internal membrane becomes delaminated, and its various laminae constitute a 
more or less dense feltwork in the interior of the cavity of the corpus luteum, “ tout 
a fait semblable a des fibres conjonctives enlace'es.” If the membrane which Bouin 
and Ancel describe in the bitch is formed and reacts to stains as they say, and if it 
takes part in the fibrillar network which afterwards appears in the interior of the 
corpus luteum, it is quite a different structure from that which I have noted in 
ferrets. In the latter animals the membrana interna does not react to stains in the 
same way as the membrana externa, and it never presents the vitreous appearance 
which is so distinctive of the external membrane ; moreover, it takes no part in the 
formation of the reticulum which appears in the interior of the corpus luteum ; on the 
