Corpora lutea in an Ascidian, Ciona
intestinalis
By D. B. CARLISLE
{From the Department of Zoology and Comparative Anatomy, Oxford)
SUMMARY
Corpora lutea are reported to be present in the ovary of Ciona intestinalis and are
briefly described. They conform to the type known as pre-ovulation corpora lutea
solida simplicia.
W
ITHIN the last decade corpora lutea have been reported present in
the ovaries of species from all classes of Gnathostomata (v. Bretschneider and de Wit, 1947). I am, however, unacquainted with any report of their
presence in lower Chordata. In the course of endocrinological investigations
in Ascidians (Carlisle, 1950) I have observed the presence of corpora lutea
in the ovaries of Ciona intestinalis L. which had been stimulated by the injection of mammalian gonadotrophin. It has been suggested to me that a brief
histological description of these bodies might be of interest. I adopt the
terminology used by Bretschneider and de Wit.
The majority of the corpora lutea of Ciona develop, under my experimental
conditions at least, by the destruction of almost mature ova rather than by the
proliferation of the remaining granulosa cells in follicles which have discharged their ova. A discharged ovum, in fact, takes with it most of or all
the granulosa cells of its follicle. The a-stage, then, is characteristically one
of invasion of the vitellus of the nearly mature ovum by granulosa cells which
phagocytose yolk granules. The oolemma becomes attenuated, and pierced
in places. I have not observed the 'explosion' of the nucleus described by
Bretschneider and de Wit in Rhodeus amarus. Instead, in Ciona, distortion of
the nucleus takes place accompanied by the intermingling of blastodisc and
vitellus. The nucleus is gradually dispersed among the cytoplasm and loses
its individuality.
The organization or /J-stage consists in the rapid proliferation of the granulosa cells which usually unite eventually to form a syncytium. Amitotic division can be observed and cells may have more than one nucleus. At this stage
the greater part of the ovum has been ingested by the granulosa cells, many
of which are greatly enlarged and possess a 'foamy' cytoplasm full of vacuoles
in the fixed preparation.
The /?- stage passes over into the y-stage or stage of decay and secretion.
The greatly enlarged 'foamy cells' are arranged peripherally, apparently disintegrating and releasing some substance; and the centrally arranged granulosa cells of the corpus luteum undergo degeneration with the formation of
yellow granules.
[Quarterly Journal of Microscopical Science, Vol. 92, part 2, June 1951.]
202
Carlisle—Corpora lutea in an Ascidian, Ciona intestinalis
The 8-stage is the final stage of disintegration. The corpus luteum at this
stage consists of a mass of necrotic cell remnants and strands of a basiphilic
nature with one or more clearly defined chromophobic areas, possibly halfdissolved remnants of cells which have not yet collapsed.
nucleus of ovum
blasfcodisc
granulosa
enlarged periphery,
granulosa cells wibh
foamy' cytoplasm
syncytium of*
granulosa cells
FIG. I . Sketches illustrating the stages of the development of the corpora lutea of Ciona
drawn from sections of material fixed in mercuric-formaldehyde and stained in Ehrlich's
haematoxylin. A. A normal, nearly mature ovum with very heavily staining spherical nucleus
and clearly defined membranes around the vitellus (oolemma) and between the vitellus and
the blastodisc. B. An early a-stage corpus luteum with invasion of the vitellus by the granulosa
cells, disruption of the oolemma, dissolution of the membrane around the blastodisc, and
distortion of the nucleus which stains less heavily, c. An early j3-stage corpus luteum. The
granulosa cells have phagocytosed most of the ovum and they have formed a syncytium.
D. A y-stage corpus luteum. A central mass of small compact cells surrounded by large cells,
with a foamy cytoplasm, which seem to be disintegrating, E. A 8-stage corpus luteum. Tattered
remnants of cells in all stages of decay. Yellow granules of some kind are present.
The four stages, which are quite arbitrary but convenient, can be summarized as:
a Invasion of the ovum.
j8 Assimilation of the material of the ovum.
y Utilization of this material and its secretion in a different form.
S The final collapse of the corpus luteum.
The corpus luteum of Ciona may be called, in the terminology of Bretschneider and de Wit, a pre-ovulation corpus luteum solidum simplex. That
is to say it is formed by the destruction of a nearly mature ovum, it has no
follicular space, and the theca takes no part in the structure. Indeed in my
Carlisle—Corpora lutea in an Ascidian, Ciona intestinalis
203
material there is little sign of the existence of a theca. The epithet 'preovulation* must not be taken to imply that the corpus luteum develops before
ovulation has taken place. When Ciona ovulates, most or all of the mature
eggs in the ovary are discharged; corpora lutea then develop by the destruction of most of the nearly mature ova. The stimuli for ovulation of the mature
ova and luteinization of the nearly mature ova are simultaneous and possibly
identical. The pre-ovulation corpus luteum then is formed after ovulation
of the ovary as a whole but in a follicle from which ovulation has not taken
place.
ACKNOWLEDGEMENTS
The work described in this paper was performed at the Zoological Station
of Naples while holding the Oxford Naples Scholarship, a Senior Demyship
of Magdalen College, Oxford, and a Beit Memorial Research Fellowship. I
wish to thank Professors A. C. Hardy and R. Dohrn, and Mr. A. E. Needham.
REFERENCES
BRETSCHNEIDER, L. H., and DE WIT, J. J. D., 1947. Sexual endocrinology of non-mammalian
Vertebrates. Amsterdam.
CARLISLE, D. B., 1950. On the hormonal and neural control of the release of gametes in
Ascidians. (In the press.)