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PROFESSOR ARTHUR ROBINSON ON 
greater than it was at the preceding stage, and so the process proceeds until the 
amount of secretion present is sufficient to enable the next or some succeeding 
generation to attain to maturity. 
In other words, the earlier generations of follicles are the pioneers which blaze 
out the pathway along which the succeeding generations advance to the promised 
land of maturity. 
In some animals, such as Dasyurus viverrinus, the secretion produced by groups 
of follicles which have died is so exhausted by the production of the maturity of 
what may be called a terminal group, that, whether pregnancy occurs or not, a 
long anoestrus period is necessary during which numerous groups of follicles may 
grow and die before sufficient secretion is accumulated to induce the maturation of 
another terminal group. 
In the guinea-pig the regular production of groups of follicles, which grow to 
a certain extent and then die, continues throughout the period of pregnancy, and 
although it is interfered with by the corpora lutea, as Beard (2) suggested it was 
in all mammals, and as Loeb (19) has proved it to be in guinea-pigs, still it occurs 
to an extent necessary to bring a terminal group of follicles to maturity at or 
about the period of parturition, and it is practically certain that the same conditions 
occur in rats and mice. 
It appears probable, therefore, that in all mammals groups of follicles are 
produced and grow and die throughout the whole period of sexual life, and that 
the majority of the groups have no possibility of attaining maturity ; nevertheless 
they have a definite function, which is to form the secretion which is necessary for 
the maturation of a terminal group of follicles. A time comes, however, at all events 
in the case of the human female, when the production of groups of follicle, or their 
growth, or their capability to form the necessary secretion, is so reduced that 
ovulation first becomes irregular and then ceases, and the menopause occurs. 
The suggestion is not invalidated by the fact that ovulation occurs after the 
menopause in a certain number of cases, for the occurrence is rare, and it is 
probable that the follicles which rupture them are not normal, inasmuch as the 
ova they extrude are rarely, if ever, capable of fertilisation. 
The Relation of the Follicles to the Pro-oestrum and (Estrus. 
In some of the preceding pages I have shown the necessity for the repeated 
production of groups of ovarian follicles, and have attempted to show that the 
attainment of maturity by special groups depends upon the life-work of the groups of 
follicles which preceded them and failed to reach maturity ; but in addition to their 
work of preparing the means for their own development, the follicles at a certain 
period of their history appear to take on the function of providing the secretion 
which is responsible for the phenomena of the pro-oestrum and the oestrus. This 
