OVARIAN FOLLICLES IN FERRETS AND FERRET-POLECAT HYBRIDS. 313 
in which the cells and fibrils run parallel with the external surface of the follicular 
epithelium, and in which are embedded small clumps of interstitial cells (fig. 49, 
PI. VIII). It differs from the other parts of the cortex only because the fibrillar 
tissue is more marked, the interstitial cells are less numerous, and as the follicle 
attains its full pre-inseminal size the small blood-vessels in the immediate neighbour- 
hood of the external limiting membrane of the follicle become so numerous that 
they constitute a definite vascular layer (figs. 19, 20, PI. Ill ; fig. 24, PI. IV ; 
fig. 48, PI. VIII ; figs. 54, 57, PI. IX ; figs. 59, 60, PI. X). 
The Sizes of Full-grown Follicles of the Pre-inseminal Stages. 
The sizes of the follicles in the pre-inseminal stages are of interest in connection 
with the changes which occur after insemination. They have been estimated by 
taking the largest follicles in each ovary of the various groups. In the accompany- 
ing tables the sizes of the follicles are given, and the number of the follicles of the 
largest size are stated. In that number are included follicles which were slightly 
smaller than the largest, but the smaller follicles of the group differed only by a 
few microns from the larger in one or more of the three diameters. The condition 
of the largest follicles, whether normal or degenerate, is noted in the tables. 
It will be seen that the follicles differ considerably in size in different ovaries, 
and that the difference is independent of the size of the animal, as judged by 
its weight. 
The average size of the largest follicles in 35 ovaries taken from 16 animals 
in the anoestrus period (Table I) is '0404 mm. 3 , the smallest follicle being ‘0025 mm. 3 , 
and the largest '1561 mm. 3 If the anoestrus series of largest follicles is broken 
up into two groups, one consisting of the largest follicles in the ovaries of animals 
killed between 11th November and 9th December of the following year, and a 
second group consisting of the largest follicles in animals killed between 5th February 
and 6th May, it is found that the average size of the largest follicles of the first 
group is '0049 mm. 3 , and the average size of the largest follicles of the second group 
is '0598 mm. 3 
The average size of the largest follicles in the ovaries in animals in heat, and 
in which no attempt at insemination was made (Table III), is '3215 mm. 3 , and if 
to this group are added the follicles of two animals which were in heat after parturi- 
tion (Table IV), the average size of the oestrus follicles is increased to '3627 mm. 3 
The average size of the largest follicles in the ovaries taken from 13 animals 
in full oestrus in which insemination was attempted, but unsuccessfully (Table V), 
is '9567 mm. 3 ; and the average in the group of ovaries taken from animals in the 
post-partum or post-abortion condition, and which were not in heat, is '2830 mm. 3 
The most important changes in the constituents of the follicles during the 
pre-inseminal period are increase in size of the ovum and alterations in its constitu- 
