OVARIAN FOLLICLES IN FERRETS AND FERRET-POLECAT HYBRIDS. 319 
maturation of the follicles is a constant and normal phenomenon, but the amount 
of fat which is deposited varies considerably in different follicles. The deposition of 
fat spherules in the follicle cells is also a constant phenomenon of the commencing 
degeneration of follicle cells ; but when the deposition of fat takes place in com- 
mencing degeneration the spherules are always of larger size, more numerous in 
proportion to the size of the cell in which they are deposited, and they tend to 
fuse together to form globules of relatively large size, and under low magnification 
of osmic preparations the dense, black, degenerate follicular epithelium is easily 
distinguished from normal epithelium (compare the left and right follicles, 
fig. 39, PL VII). 
After insemination no very definite changes beyond the nuclear migration occur 
in the general follicular cells, except in the region of the cumulus. There the 
dispersion of the follicle -cell by the secondary liquor folliculi is a marked pheno- 
menon, and the migration of the nuclei, which lay close to the oolemma, commences 
and proceeds regularly till the corona radiata is fully developed, when all the 
nuclei of the corona lie in the peripheral ends of the cells to which they belong 
(figs. 41, 42, 43, 44, PI. VII). At the same time the corona cells become greatly, 
but unequally, elongated, with the result that the surface of the corona appears 
to be formed by a number of projecting spokes of different lengths, a condition 
which probably facilitates the effect of the rush of fluid which sweeps the ovum 
through the cavity of the ovarian capsule into the oviduct. 
The chondriosomes of the corona epithelium are similar to those of the general 
follicle cells, that is, they are rods and filaments of varying size which lie parallel 
with the long axes of the cells, and, where the inner ends of the corona cells 
blend with the outer part of the oolemma, the chondriosomes appear to pass into 
the substance of the oolemma (fig. 43, PI. VII; fig. 45, PI. VIII). 
Discussion. 
Membrana limitans externa. 
Unlike the membrana limitans interna, the external limiting membrane (fig. 52, 
PI. IX ; fig. 59, PI. X) has received a large amount of attention. It seems to be 
universally present, for although Benckiser (3), Schottlander (36), and Sandes 
(35) say that it is absent in the pig, Monterosso (27) figures and describes ovarian 
follicles of that animal, and says that “ Tra la membrana basilare o propria folliculi 
e la theca interna e interposto uno strato quasi continuo di cellule grandi,” a state- 
ment which indicates that interstitial cells are present in the pig, and which is not 
in accord with Frankel’s account of the ovaries of the pig. 
Whilst the presence of the external limiting membrane is well known, there 
is difference of opinion regarding its constitution. Wagener (41), Schottlander 
(36) , and Limon (18) look upon it as a connective tissue structure, though they 
TRANS. ROY. SOC. EDIN., VOL. LII, PART II (NO. 13). 51 
