338 
PROFESSOR ARTHUR ROBINSON ON 
sufficient to justify a positive statement ; whilst, at the same time, they seem to 
point towards the conclusion that, in animals which ovulate only after coition, 
something is present which prevents ovulation until it is neutralised by coition, and 
that it is not present in spontaneously ovulating animals ; or conversely, that in 
spontaneously ovulating animals something is present which favours ovulation, it is 
absent in animals which only ovulate after coition, and that it is provided by coition ; 
but, in either case, there is no evidence to show what the substance is, or how or 
where it is formed. 
Summary. 
In ferrets and ferret-polecat hybrids successive generations of ovarian follicles 
are formed throughout the whole period of life. 
In the interval between two ovulations, whether the period be long or short, 
successive groups of follicles grow and die, at successively advanced stages, until a 
group attains to full maturity. 
It seems probable that the follicles of one group produce material which favours 
its own growth and facilitates the further advance of succeeding groups. 
The phenomena of the pro-oestrum and the oestrus only appear when a group of 
follicles has attained a stage of development which may be called pre-inseminal 
maturity, and the phenomena are due to some secretion produced by the follicles in 
that phase of their development. 
The follicles only become fully mature and only rupture after spermatozoa have 
entered the caudal third of the oviduct. 
The rupture of the follicles is due to the formation of the secondary liquor 
folliculi which follows successful insemination. 
There is no bleeding when rupture occurs, either into the follicles or at the 
margins of the apertures in their walls, and bleeding only occurs occasionally during 
the redistension of the follicles. 
The greater part of the follicular epithelium remains in the follicles after the 
rupture and the extrusion of the ovum and the cumulus cells. 
After the rupture the follicles redistend, and the redistension is associated with 
the transformation of the follicle cells into lutein cells. 
