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PROFESSOR ARTHUR ROBINSON ON 
supported by the specimen F.D.A. 45/15 (Table IV), which was killed on the thirtieth 
day of her second oestrus, for in her ovaries were not only follicles of full pre-inseminal 
growth-size, both normal and degenerate, but also follicles which had evidently 
attained that stage and had then undergone atrophy as well as other follicles of 
comparatively large size, apparently approaching to full growth. 
After insemination and the rupture of the mature follicles, follicles of full post- 
inseminal and pre-ruptural growth-size are found in a certain number of ovaries ; 
but such follicles always show definite signs of abnormal conditions, and though 
they may become luteal, they do not rupture (fig. 38, PI. VI). 
Follicles of full pre-inseminal growth-size are present in the ovaries of pregnant 
animals up to the twentieth day of pregnancy. . From the twentieth to the thirtieth 
day no follicles of that size were found. They are present again at the thirty-sixth 
day, and in increasing numbers to the forty-second day, which is the termination of 
the full period. Among the largest follicles present at any given day of pregnancy, 
some are always normal and some degenerate. It appears, therefore, that throughout 
the whole period of pregnancy, growth and death of groups of follicles continues with 
a diminution of the largest size attainable during the middle of the period. But 
whilst the size of the largest follicles during the middle of the period of pregnancy 
is less than the size of the largest follicles in the early and late parts of that period, 
it is never so small as the size of the largest follicles of the early part of the anoestrus 
period. It is obvious, therefore, that the largest follicles present at the beginning of 
pregnancy all disappear by the middle of pregnancy, and that they are replaced by 
younger follicles ; but there is no evidence to show which of the younger follicles, 
the primitive or those more advanced of the early period, become the lar’gest follicles 
of the later period. The facts as they stand, however, lend basis to the assumption 
that a follicle takes at least half the time of the period of pregnancy, that is, 
twenty-one days, to pass from its primitive condition to the condition of full 
pre-inseminal growth. 
The conditions met with in the' ovaries of ferrets during the gestation period are 
similar in all essential respects to those described by Loeb (19, 19a) in guinea-pigs, 
and it is obvious that in both groups of animals corpora lutea, as such, have no 
detrimental effect on the growth of the follicles ; but whilst they do not prevent the 
growth, they do, in the guinea-pig, prevent the ripening ; for Loeb finds that when 
the corpora lutea are totally extirpated in that animal, in a certain number of cases 
ovulation may occur during pregnancy. But whilst under ordinary circumstances 
the corpora lutea do not prevent the growth of follicles, there are cases in the ferret 
where the number and sizes of the corpora lutea are so great that the remaining part 
of the cortex of the ovary is reduced to a minimum ; in those cases the growth of 
the follicles is interfered with, but that is due to the circumstance that there is 
neither room nor, probably, is there pabulum sufficient for the growth which is more 
usually met with at the corresponding periods of gestation. 
