OVARIAN FOLLICLES IN FERRETS AND FERRET-POLECAT HYBRIDS. 325 
D.A. 42/15 (Table II). Cast 11 young on 11th May, and was not in heat when 
killed on 8th June. Corpora lutea corresponding with last pregnancy, 8 in one 
and 5 in the other ovary. Both ovaries contained follicles of full pre-inseminal 
growth, and the animal would probably have shown signs of the pro-oestrum in a 
few days. 
F.D.A. 45/15 (Table IV). Cast 8 young on 21st May, which were all dead the next 
day. In full heat on 7th June. Killed 2nd July. Corpora lutea corresponding with 
the previous pregnancy, 10 in one and 8 in the other ovary. Both ovaries contained 
follicles of full pre-inseminal growth. 
The ovaries of all five animals contained a considerable amount of cortical tissue 
not encroached upon by the degenerating corpora lutea. 
In spite of these apparently adverse facts a survey of the ovaries of all the 
animals at my disposal shows that the sizes of the corpora lutea vary greatly both in 
the same and in different animals. They also show that although the space occupied 
by the corpora lutea is relatively large, a considerable portion of the cortical tissue 
remains in most cases as in the above mentioned for animals, and that it frequently 
contains follicles of considerable size, whilst in a certain number of cases, as already 
stated, the corpora lutea practically usurp the whole of the cortical area, and only a 
few very rudimentary follicles can be found. In these latter cases it seems impos- 
sible to believe that the cortex can be reconstituted and follicles developed in time 
for a second oestrus. 
There are other factors, with which this inquiry is not concerned, which interfere 
with the occurrence of a second oestrus in one season, but the point already noted 
raises the question of the amount of time occupied by the follicle in passing from its 
initiation to its full pre-inseminal growth. The data at disposal cannot, of course, 
give a positive answer to the question, for it is not possible to follow the life-history 
of any given follicle, but they offer interesting suggestions. 
Table I shows that the size of the largest follicles in the ovaries of anoestrus 
animals gradually rises from the middle of November to the early part of April, the 
breaks in the series being due in all probability to the fact that some of the animals 
were young adults born late in the previous season. It shows further that of the 
follicles of largest size, or about largest size, a considerable proportion are in a state 
of degeneration, and that that proportion is relatively the same throughout the 
whole period. Under these circumstances it seems scarcely possible to assume that 
the largest normal follicles of the earlier part of the period persist and become the 
largest normal follicles of the later part of the period ; on the contrary, it seems more 
reasonable to suppose that all the largest follicles of the earlier part of the period die 
and are replaced by other follicles, which, as the oestrus period approaches, are able 
to attain a more advanced stage of development, until, finally, some attain to full 
pre-inseminal growth, but not to full pre-inseminal development. This supposition is 
