absent from the pre-ovulatory follicle. The collagen fibres were
arranged more irregularly at this stage and the intercellular space
was considerably increased; it appeared to be filled by a fine granu-
lar material, possibly a protein solution in life. Within 24hrs signs
appeared that some of the thecal cells were undergoing degenerative
changes; the mitochondria tended to swell, the cell membrane was dis-
rupted in places and slight vacuolation was noticeable in the cyto-
plasm. These changes became progressively more marked, although not
all cells were affected and even after 48hr there were many viable
cells present.

The theca interna was characterised by more rounded cells and
there were no signs of an intracellular fibrillar layer characteristic
of those cells of the theca externa. There was relatively less
colagen and this was not so regularly distributed. Much of the
intercellular space was filled with an electron-dense granular
material. There were also many prominent, small blood vessels,often
closely associated with the basement membrane. After ovulation
changes occurred in the cells which were similar to those in the theca
externa: the cells contracted but did not become so markedly irregular
and vacuoles appeared in the cytoplasm. The intercellular granular
material so clearly evident in the pre-ovulatory follicle was reduced
in content. There was evidence which indicated that some of the
blood vessels were becoming occluded by laying down of cells within
the lumen, Throughout the theca interna of the pre-ovulatory
follicle there are small spaces between the cells which suggest that
secretory droplets are formed by some of the cells; these may be
lipid. Within a few hours of ovulation, particularly along the theca
interna and externa junction these vacuoles become progressively more
numerous; moreover similar droplets appear in, what are now at this
stage, specialised cells., These cells may be equivalent to the
luteal cells described by earlier histologists. Within 24hrs these
cells are very prominent and are filled by numerous clear vacuoles.

The basement membrane of the pre-ovulatory follicle was composed
of an amorphous material and projections from it seemed to fill the
spaces between the granulosa cells. Wyburn et al. (13 ) implied
that this perivitelline material in the pre—ovulsfory follicle was
structureless, but this was not found to be so in the present work:
small tubules and vacuoles were present. Moreover the space was
much less than shown by Wyburn et al. (13 ). With the contraction
of the follicle after ovulation the basement membrane became much
folded and, in places, detatched from the theca interna. This in
turn clearly disrupted some of the blood vessels of the theca and
many blood cells were found in the spaces so formed. Of more
interest were the cells containing large granules which were found
scattered along the thecal side of the basement membrane; these were
not apparently present before ovulation, The basement membrane also
appeared to hypertrophy and scattered throughout it were dense drop-
lets; these may have been derived from the thecal or granulosa cells.

It is well known from earlier work that major changes occur in
the gramulosa cells and later Wyburn et al. (13 ) from an electron
microscopical study suggested a progreséf;e change in an homogenous
cell population, The results of the present work indicate that this

  

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