Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. Ii

OBSERVATIONS  ON THE ULTRASTRUCTURE OF THE POST-OVULATORY

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FOLLICLE OF THE DOMESTIC HEN. by A.B. Gilbert, Agricultural
Research Council's Poultry Research Centre, Edinburgh.

The fully mature avian follicle is a large, slightly oval struc-
ture of about 3cm diameter attached to the ovary by a short stalk.
Immediately after ovulation the follicular walls contract to a length
of about 14mm. ( Subsequent to this there is a further general reduc-
tion in size and the 'yellow body' is formed within the cavity. After
about 5 days the post-ovulatory follicle is about 2mm long and within
7-10 days it is barely apparent to the naked eye.

There has been a considerable controversy as to whether the post-
ovulatory follicle in the bird is a corpus luteum (1,3,4,5,6,9,10) and
this appears to have arisen from a desire of some workers to equate
the structure in mammals with that in birds without understanding the
fundamental differences in reproductive processes between the two
groups. In the mammal the ovum, and the subsequent foetus, remain in
the oviduct for periods ranging from a few weeks to several months
depending on the species. The corpus luteum usually remains active
for most of this period and is concerned with maintaining pregnancy at
least for some part of this time; removal of the corpus luteum leads
to abortion. On the other hand, in the chicken the ovum remains in
the oviduct for little more than 24hrs. although the post-ovulatory
follicle is present for much longer periods. Removal of the post-
ovulatory follicle within this 24hr-period caused a retarded laying of
the egg derived from that follicle (2,11) and affected the nesting
behaviour associated with it (8,12). Removal of other post-ovulatory
follicles, which are histologically more similar to the mammalian )
corpus luteum, appear to have little effect on reproductive activity.

There has been little work on the general ultrastructure of
either the pre- or post-ovulatory follicle: the work of Bellairs,
Schjeide and others (see Gilbert, (7) for review) was concerned mainly.
with yolk formation and Wyburn, Johnston & Aitken (13) reported on the
fate of the granulosa cells only.

This paper deals with some of the preliminary findings with the
electron microscope of a systematic study of the structure of the
post-ovulatory follicle within the first 24hr which could be related
to its function during this period.

In the pre-ovulatory follicle, the theca externa was found to
consist of extremely elongated cells (sometimes more than 200u long)
arranged in a circular pattern around the circumference of the follicle.
These cells had a prominent endoplasmic reticulum and ribosomes, and
the mitochondria tended to be elongated. On the inner border of the
cell membrane was found a layer of unusual material apparently com-
posed of fine filaments. Interspersed between the cells were
collagen fibres and these were regularly arranged usually at right
angles to the length of the cells. There was very little inter-
cellular space except that surrounding the collagen fibres. Immediately
after ovulation the elongated cells had contracted to an extremely
irregular shape with long 'amoeboid' processes thrown out into the
surrounding areas. There was no sign of the intracellular fibrils.
However just exterior to the cell wall appeared a dense amorphous
material which may have been composed of packed fibrils. This was

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