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PROFESSOR ARTHUR ROBINSON ON 
cause of the growth of the follicles ? 2. Why do many follicles die before attaining 
maturity ? 3. What is the cause of the rupture of the follicles ? To these questions 
the conditions met with in the ovaries of ferrets suggest certain answers, but they 
furnish no absolutely conclusive proofs that those answers are correct. Such 
absolute proof can only be obtained by experiments, which will be very difficult to 
carry out on account of the intimate relations of the parts of the ovary which 
are involved. 
The cause of the growth of the follicles is either intraovarian, extraovarian, or 
partly one and partly the other. 
It is possible to suppose that the cause of the growth of the follicles is extra- 
ovarian, and that it is due to some supposititious substance, such as the “ gonadin ” 
invoked by Heape as the cause of the general phenomena of the pro-oestrum and 
oestrus ; but if that supposition is admitted, it is necessary to account for the fact 
that the majority of the follicles formed fail to become mature ; for whilst it may 
be granted that some of the follicles die because their positions in the ovary are 
unfavourable to complete development, as both Heape (ll) and Loeb (19) suggest, 
that explanation does not account for the fact that, both in the guinea-pig and the 
ferret, many generations of follicles, which appear in the ovaries at certain periods, 
die before attaining to maturity, unless it is assumed that the substance formed 
outside the ovary and carried to it by the blood-vessels is first formed in small 
quantity sufficient to produce a moderate amount of development and then fails, 
later in larger but still insufficient amount and again the supply fails, until finally an 
amount sufficient to carry the follicles to their maturity is provided ; and that these 
conditions recur again and again in regular sequence. This is a supposition difficult 
to entertain, and although extraovarian influence has not been excluded, no series of 
observations or experiments hitherto made has provided it with any appreciable basis 
of support. If, therefore, we leave aside the possibility of extraovarian influence and 
turn to the ovary for an explanation of the growth of its follicles, there are three 
parts of the organ which at once suggest possibilities : (l) the interstitial tissue, (2) 
the corpora lutea, and (3) the follicles themselves. It is generally admitted that 
both the interstitial tissue and the corpora lutea do produce secretions which pass 
into the blood and influence the activities of other organs, but it is not so generally 
admitted that the follicles are also endocrine organs. Nevertheless it is possible, as 
I will attempt to show, That the follicles, once formed, are the cause of their own 
further evolution. 
A certain number of primitive follicles of any given group or generation are 
capable of obtaining from the surrounding blood and lymph vessels sufficient 
nutriment to enable them to grow until they become follicles with a single layer 
of cubicular or columnar follicle cells. As the follicle cells assume their cubical 
or columnar shape they acquire also all the characteristic features of secreting 
cells (figs. 6 and 7, PI. I). It may be argued, and it is frequently assumed, that 
