OVARIAN FOLLICLES IN FERRETS AND FERRET-POLECAT HYBRIDS. 327 
In other animals, such as rats, mice, and rabbits, in which ovulation does, or can, 
take place immediately after parturition, it is very probable that the growth of the 
follicles occurs during pregnancy, much in the same way as in guinea-pigs and ferrets, 
the only difference between the various animals being that, in those in which 
ovulation is not dependent on insemination, some follicles reach full maturity during 
gestation, whilst in the ferret they only attain to full or almost full pre-inseminal 
growth, a point which will be referred to again in the consideration of the causation 
of oestrus. 
Whether the conditions met with in the ovaries of ferrets, during the gestation 
which intervenes between two oestrus periods, occur also in the ovaries of polyoestrus 
animals is doubtful, and, so far as the human subject is concerned, the statements 
made by different observers are extremely contradictory. Unfortunately, most of 
the observers who have dealt with human material have been chiefly concerned in in- 
quiring as to whether or not ovulation occurs during pregnancy, and on that point they 
are practically all agreed ; it either does not occur or is very exceptional ; neither does 
it occur in any other animal, being prevented, according to Loeb’s observations, by 
the corpora lutea ; but ovulation is only the termination of completed follicle growth, 
and there is considerable difference of opinion as to what extent follicle growth takes 
place in the human ovary during pregnancy. 
Seitz (37), who examined the ovaries of thirty-six pregnant women, was unable 
to find ripe or nearly ripe follicles in any of them, and he throws doubt on a case of 
Consentino’s, which he quotes, in which a recently ruptured follicle was found in the 
ovary of a woman in the sixth month of gestation. The more recent researches of 
Leopold and Raveno (17) and those of Raveno (31), which were carried out on a 
large number of cases, do not support Seitz. 
Raveno, as the result of his observation of a series of sixty cases, writes : “In 
alien Eierstocken fanden sich Graafsche Follikel auf dem Wege der Reife ; ei einige 
schon reif und im Begriff zu platzen, aber ein frisch angebrochener Follikel wurde 
niemals beobachtet” (3l). 
Hill and O’Donoghue (12) state' that the rupture of a group of follicles in 
Dasyurus viverrinus, which is monoestrus, and which ovulates spontaneously, is not 
followed by the growth of a fresh batch of follicles, whether the animal becomes 
pregnant or not ; but they do not state that follicle growth completely ceases either 
after ovulation without pregnancy or during pregnancy, and it appears, from what is 
known with regard to other animals, that follicle growth proceeds throughout the 
whole or the greater part of extrauterine life — even in the human female, after the 
menopause, according to Leopold and Raveno (17). But whilst this must be 
admitted in view of the evidence which is available, it must be noted that the state 
of development to which the follicles can attain varies considerably at different 
periods of life. 
In association with these facts three questions at least arise : 1. What is the 
TRANS. ROY. SOC. EDIN., VOL. LII, PART II (NO. 13). 52 
