332 
PROFESSOR ARTHUR ROBINSON ON 
scattered cells, but they do not form so prominent a feature of the ovarian structure 
as in the cat and ferret. 
Moreover, Marshall’s experiment, though it is apparently accepted by Paton 
(30) as conclusive, is not adequate to support the contention based upon it. It 
provides no proof that the capabilities of the cells of the ruptured follicles were 
interfered with, and there is every reason to suppose they were not. The intra- 
follicular pressure was temporarily reduced, but it was, obviously, soon re- 
established, for Marshall notes what he takes to be the abnormal size of the follicles 
in the first animal when it was killed, a week after oestrus had commenced and three 
and a half weeks after the operation. Such considerable redistension of the normally 
ruptured follicles is not unusual in ferrets, and-is only one of the phases met with in 
the formation of the corpora lutea. 
In all young animals group after group of follicles grows and dies, but no signs 
of heat appear, because none of the groups have attained to the phase of growth 
during which they form the heat-producing secretion. Again, in sexually mature and 
adult guinea-pigs and ferrets group after group of follicles grows and dies without 
attaining the stage at which the heat-producing secretion is formed ; but once a group 
of follicles has attained to that stage which is shown in the ferret (fig. 13, PL II ; figs. 
15, 16, PL III), when the cumulus epithelium begins to show signs of separation into 
an outer and an inner group of cells, the phenomena of the pro-cestrum followed by 
those of the oestrus appear. It was probably just before this stage was attained that 
Marshall punctured the follicles, but it is obvious that the puncture did not prevent 
the subsequent growth and the transformation of the follicle cells info luteal cells, 
which Marshall describes, and thinks, were of abnormal character. Even if that was 
the case, it is clear that the follicle cells had passed successfully through the phases 
which precede their transition into luteal cells, and it is in those phases that they 
produce the secretion which gives rise to the phenomena of heat. 
The preceding statement is not merely the expression of a supposition, for the 
ferret furnishes practically conclusive information with regard to the point at issue. 
I have shown, and a reference to the accompanying tables of notes will confirm 
the statement, that the ferret does not ovulate unless it is properly inseminated, and 
by proper insemination I mean unless spermatozoa enter the caudal third of the 
oviduct, for the excitement of the act of copulation may occur without subsequent 
ovulation (see Table Y), although the follicles in the ovaries are at the stage 
of growth at which rupture would occur if insemination were successful. After 
insemination has been unsuccessfully attempted the phenomena of heat continue, 
and if the female is placed with another male, successful insemination can be attained. 
If insemination is successful, the phenomena of heat disappear as the follicles pass to 
their later phases of development ; but if the female in heat is kept separate from the 
male, the phenomena of heat continue. In one of Marshall’s specimens it lasted 
for a period of five weeks (21) and then terminated; in another it was still present 
