33.4 
PROFESSOR ARTHUR ROBINSON ON 
that, it should be noted that the suggestion that the follicles produce the substance 
which facilitates their own growth, and also that on which the phenomena of heat 
depend, is not in disaccord with Heape’s contention that the phenomena of the oestrus 
period are dependent on climatic and food conditions, for it is obvious that the 
necessary pabulum must be provided for both purposes, and, under ordinary condi- 
tions of life, it is probable that the proper pabulum is only attainable at certain 
seasons, whilst in the cases of domesticated animals it is provided all the year 
round ; thus by the artificial alteration of external conditions it is possible that a 
normally moncestrus animal might be converted into a polyoestrus animal. 
The Cause of the Rupture of the Follicles in Ferret and Ferret- Polecat Hybrids. 
In ferrets and ferret-polecat hybrids no ovarian follicles rupture unless sper- 
matozoa are present in the caudal third of the oviduct ; moreover, the rupture does 
not take place at the same time after copulation in all animals. It may occur 
about thirty hours after copulation, and it may be delayed for over ninety hours 
(see Tables VII, IX). 
In the specimens in which ovulation was delayed, follicles of normal size and 
structure were present in the ovaries, but the ova in some had not passed into the 
stage of the first maturation division, and in others were only attaining that stage 
at a later period. 
It is well known that animals will not permit sexual congress unless they are in 
heat, and heat is always associated with follicles which contain ova which are in the 
first maturation division phase, or which are ready to pass into that phase as soon as 
the necessary stimulus is provided. Therefore the animals in which spermatozoa 
were found in the oviducts must have been in oestrus ; their ovaries all contained 
follicles in the stage of pre-inseminal maturity. The only difference which could 
be detected between those in which ovulation followed insemination after a relatively 
short period and those in which ovulation was delayed was the number of sper- 
matozoa in the caudal thirds of the oviducts. 
In those cases in which the spermatozoa were numerous ovulation occurred 
relatively soon, and in those in which the spermatozoa were few in number ovulation 
was delayed. 
In those animals in which the spermatozoa in the oviducts are numerous the 
dispersion of the cumulus epithelium, the formation and extension of the secondary 
liquor folliculi, the phenomena of the first maturation division of the ovum, and the 
rupture of the follicles take place relatively quickly, whilst in those in which few 
spermatozoa are present all the phenomena are retarded. 
It appears, therefore, that, in the case of the ferret, the final phenomena of the 
maturation of the follicles and their rupture are due either to the spermatozoa or to 
the seminal fluid. 
