THE DEVELOPMENT OF THE MOLE. 159 
zona by a slightly dilated mouth, while on the outer side of 
the zona they communicate with tie exterior by a considerably 
wider opening (fig. 7). Into the external openings of these 
canals I have been able to trace prolongations of those cells 
of the discus which are immediately in contact therewith 
(fig. 7), and there appears to me no room for doubt that the 
contents of these follicular cells are thus rendered available 
for the nutriment and growth of the ovum. 
Owing to the extreme minuteness of the canals it is quite 
possible that they are only rendered visible by the protoplasm 
of the follicular cells, which is less transparent than the zona 
itself, passing through them, and the fact that careful observers 
have not succeeded in detecting these pores would be accounted 
for by the cessation of the nutrient process at the time of 
observation. I may add I have observed the radial canals 
through the zona in optical sections of various whole ova, as 
well as in many actual sections of ova situated within the 
Graafian follicle. 
I have before mentioned that the close investment of the 
ovum with follicular epithelium cells is in accordance with the 
degree of ripeness of the ovum itself. When the latter is fully 
mature only a very small number of, and in some instances no, 
epithelium cells are carried out with it upon the rupture of 
the follicle. Thus the attachment of the epithelium to the 
zona ceases when the ovum becomes mature, and no further 
nutriment is required, and this is of itself some further proof 
of the nutrient function of the follicular epithelium cells. 
I myself never detected any follicular cells within the zona, 
such as has been described by Lindgren (No. 15), von Sehlen 
(No. 21), and Virchow (No. 22); nor have I seen any trace of 
a micropyle in the zona, such as M. Barry (No. 8) and others 
held to exist. 
Tue Virecyine MemsBrane. 
Within the zona radiata and enclosing the ovum itself in all 
those ripe ovarian ova examined by me, is a second very thin 
