/ . Embryol. exp. Morph. Vol. 20, 1, pp. 1-13, August 1968
With 2 plates
Printed in Great Britain
The inductors of
differentiation of prefollicular tissue and the
follicular epithelium in ovarioles of Pyrrhocoris
apterus (Heteroptera)
By PETR MASNER 1
From the Department of Developmental Morphology, Institute of
Entomology, Czechoslovak Academy of Sciences, Prague
Differentiation of the tissues of the telotrophic ovarioles from the embryonic
primordium occurs gradually throughout larval development of bugs. All
tissues are established already at the beginning of the last larval stage as observed by Wick & Bonhag (1955) in Oncopeltus fasciatus. During the last instar,
when the corpora allata are morphogenetically inactive, the synthetic activity
of the cells of first ovarian nutritive system, the trophocytes, takes place. The
nutrients released by trophocytes at the final emergence activate the oocytes,
starting previtellogenesis (Masner, 1966). The function of this nutritive system is
known to be independent of any humoral control (Wigglesworth, 1936, and
others). Food intake seems to be the only inductor of trophocyte growth. The
developing oocyte grows into the prefollicular syncytium. The surrounding tissue
starts to organize into a unilayered epithelium.
The renewal of corpus allatum activity and the release of the juvenile hormone
(JH) is necessary for further vitellogenesis. The follicular epithelium, representing the second nutritive ovarian system, has to be activated by the hormone
(Wigglesworth, 1936; Pfeiffer, 1936, 1939; Joly, 1945; Engelmann, 1959; Joly,
1960; Highnam, Lusis & Hill, 1963; Slama, 19646). The activated cells play an
important role in supplying the oocyte with yolk, forming material either
regulating or assisting in the transmission of yolk precursors from the blood
(Telfer, 1965). Thus JH exerts a direct control of oogenesis, whereas the activation hormone (AH) from the neurosecretory cells is said to regulate this process
only indirectly, by making materials available for vitellogenesis (Highnam,
1964).
Oogenesis is inhibited after previtellogenesis in the absence of JH, i.e. when
the first nutritive system should be replaced by the second one. The oocytes
1
Author's address: Institute of Entomology, Cechoslovak Academy of Sciences, Vinicna 7,
Prague 2, Czechoslovakia.
TEEM 2 0
2
PETR MASNER
deteriorate and are referred to as being resorbed by the invading follicular cells
in Rhodnius prolixus (Wigglesworth, 1936).
The aim of the present investigation was to study the induction of differentiation of the prefollicular tissue and follicular cells, and particularly the endocrine
control of these processes. Moreover, the process of oosportion was examined,
especially as to the role of the follicular cells.
MATERIALS AND METHODS
Material of allatectomized and cardiac-allatectomized females, operated immediately after the imaginal ecdysis, was obtained by the courtesy of Dr K.
Slama. They, as well as controls, were reared together with males at 25 °C and
with an 18 h light-day and dissected 15 days after the operations.
The material was treated with Carnoy's fixative, dehydrated and transferred
into paraffin through methyl benzoate-celloidin mixture according to Peterfy.
It was cut into sections 5 /* thick. The sections were variously stained with
Heidenhain's haematoxylin in Masson's trichrome combination, gallocyanin,
Una-Pappenheim's method (modification for sections); Brachet's pyroninmethyl green method; toluidin blue controlled by ribonuclease treatment; and
Hotchkiss's PARS method (according to Pearse, 1961). The method of Wigglesworth (1959) (OsO4-ethylgallate followed by ester wax embedding) was used to
show cytoplasmic details. Feulgen, celestin blue and a combination of both
were used for measuring the size of nuclei. This was done with a calibrated eyepiece. The volume of the nuclei was calculated according to Palkovits & Fischer
(1963) using the formula V = %n (LB)$ for spherical and the formula V = %TTB2
for elliptical nuclei (L = length of the longer diameter, B = half of the shorter
diameter in perpendicular position). The mean value was calculated from
600 measurements and the standard deviation was established.
RESULTS
Control females
The germarium of the ovarioles of newly emerged females is definitely
formed. The connective and peritoneal tissues are fully differentiated, all
oogonia having differentiated into trophocytes and oocytes. At the top of the
germarium there is still a small group of trophocytes with small nuclei often
showing mitotic activity. The nuclei of the trophocytes in lower parts have
grown endomitotically and have dense, coarsely granulated, chromatin. They
are subsequently converted by autolysis into RNA-rich material, concentrated
in the central trophic core, which has just been formed. The lowest part of the
core projects into the plasmatic trophic cords in consequence of the growing
internal pressure of the nutrients. The cords reach the young oocytes found at
the end of germarium. The oocyte nuclei rest in prophase of the first meiotic
division.
Follicular differentiation
3
The prefollicular syncytium of the ovariole of the last stage larvae represents
the base of vitellarium. The true vitellarium is organized later, during oogenesis,
starting when the adult emerges. The prefollicular tissue remains, however, still
preserved at the beginning of vitellarium. It is syncytial with small spherical
nuclei, volume 13-02/*m3 (Text-fig. 1) with few faint chromatin granules,
scattered particularly along the nuclear membrane. They show high mitotic
activity and there is little cytoplasm (Plate 1, fig. A).
5000
1287
1000
788
500
100
75
50
15
16
13
PFT
PV
CHF
PV
R
AE-CAE
Text-fig. 1. The volumes of nuclei of the follicular epithelium in ft? in different
stages of oogenesis in normal and operated females plotted on a logarithmic scale.
PFT, Prefollicular tissue; PV, end of previtellogenesis; V, end of vitellogenesis;
CHF, chorion formation; PV-AE-CAE, end of previtellogenesis in allatectomized
and cardiac-allatectomized females; R-AE-CAE, resorption in allatectomized and
cardiac-allatectomized females.
The oocytes which have successfully reached the junction with the trophic core
by a cord are activated and the first period of oogenesis, previtellogenesis,
starts. The trophocytes supply the oocyte with RNA-rich material through the
cords (Plate 1, fig. A). The ooplasmic ring swells up and the enlarging oocyte
grows into the prefollicular syncytium, which starts to organize into a multilayered epithelium (Plate 1, fig. B). The nuclei of the cells are nearly the same as
in prefollicular tissue, dividing occasionally by mitosis. The unilayered epi-
4
PETR MASNER
thelium of differentiated columnar cells appears at the end of previtellogenesis
(Plate 1, fig. C).
The patches of prefollicular tissue trapped between two neighbouring oocytes
differentiate into interfollicular plugs. They consist of long transverse spindlelike cells with elliptical nuclei.
The JH present in the blood induces further changes within the follicular cells
just after the unilayered epithelium has been formed. This process begins already
before the oocyte completes previtellogenesis. The cytoplasm becomes dense,
the nuclear chromatin is endomitotically replicated and the whole nucleus
grows rapidly until it fills up much of the cell. Amitotic division of nuclei then
begins although cytokinesis does not follow and binucleate cells are formed.
The nuclei are situated one above the other and the volume of them both is 75 ju?
at the end of previtellogenesis (Plate 1, fig. C; Text-fig. 1).
Vitellogenesis begins after the follicular wall is transformed into the epithelium
of secretory cells, enabling the material essential for yolk formation to penetrate into the ooplasm. The cells come to be separated one from another by
intercellular spaces 0-5-1 fi broad. This feature corresponds with Telfer's (1961)
observation in a saturnid moth. The spaces observed in the vitellogenic follicle
have never been observed in previtellogenic follicles of the same ovariole. This
suggests that the feature is not an artifact caused by fixation. Material from the
haemolymph passes through these spaces. The dense cytoplasm of the follicular
cells is rich in RNA, especially along the inner margin of the cells. A narrow
ooplasmic layer with faint traces of microvilli alongside the follicular cells also
suggests this transport (Plate 1, fig. D). This layer seems to correspond to the
follicle cell/oocyte interface recognized by electron microscopy in Hyalophora
cecropia by King & Aggarwal (1965). The first granules of protein yolk bodies
and carbohydrates appear in the cortical layer of the ooplasm. The material
passing through the epithelial wall keeps on increasing, particularly after the
PLATE 1
Fig. A. Prefollicular tissue with small nuclei at the base of the vitellarium. Young activated
oocytes are seen above left and below right; the latter one is attached to the slender trophic
core in the middle. Feulgen, celestin blue (FCB).
Fig. B. The multilayered epithelium from the follicular wall of the young previtellogenic
oocyte. FCB.
Fig. C. The follicular cells of the oocyte at the end of previtellogenesis. The growing nuclei
dividing amitotically are situated one above the other. FCB.
Fig. D. The follicular wall of the oocyte at the beginning of vitellogenesis. Note narrow intercellular spaces, follicle cells/oocyte interface (arrow) and yolk granules. PARS.
Fig. E. The follicular cells of the oocyte at the end of vitellogenesis. Each cell contains two
enormously enlarged nuclei side by side with conspicuous nucleoli. Intercellular spaces
indistinct. Methyl green-pyronin.
Fig. F. The secretory follicular cells with enlarged nuclei (above) and the interfollicular tissue
with small nuclei (below). PARS.
J. Embryol. exp. Morph., Vol. 20, Part 1
PETR MASNER
PLATE 1
facing p. 4
/. Embryol. exp. Morph., Vol. 20, Part 1
PETR MASNER
PLATE 2
Follicular differentiation
5
complete obliteration of the trophic cord. The continuous growth of nuclei seems
to be an essential condition for this activity. The nuclear volume is 788 /iz at the
end of vitellogenesis and finally 1287 /on 3 during chorion formation, which represents a 100-fold increase over the original volume. The nuclei of the majority of
the flat cells divide amitotically. They are situated side by side and contain
coarsely granular chromatin (Plate 1, fig. E; Text-fig. 1).
The cells of the interfollicular plugs do not follow the same transformation
sequences as in the follicular cells. Their cytoplasm remains thin. The nuclei are
elongated, but their growth may be negligible. Their chromatin does not increase, and amitosis and binucleate cell formation has never been observed
(Plate 1, fig. F).
The follicles emptied after ovulation are shrunken and numerous Feulgenpositive bodies may still be observed. The tissue then disintegrates and is
pushed into the mouth of the pedicel, where the corpus luteum is formed
(Plate 2, fig. A). This is only slightly RNA-positive. The corpus luteum is characterized by a broad structureless slightly staining mass, representing the transformed wall of the pedicel (Masner, 1966).
Experimental females
The same results were obtained from allatectomized as well as cardiac-allatectomized females. The germarium is regularly arranged, the trophocytes fully
functioning, and the vitellarium continuously supplied with activated oocytes.
These oocytes grow into the prefollicular tissue, where mitotic activity is still
high. The whole course of previtellogenesis, when the oocyte is nourished by
trophocytes, is normal. The oocytes complete previtellogenesis and their further
development stops.
The growing oocyte is enveloped by a unilayered follicular epithelium, and
PLATE 2
Fig. A. Corpus luteum (middle) between the vitellogenic oocyte (left) and pedicel (right).
Note the unstained mass at the border. Heidenhains' haematoxylin, Massons' trichrome.
Fig. B. The follicular wall of the oocyte of allatectomized female. Small nuclei are located
regularly alongside the outer margin; neither intercellular spaces nor the yolk granules are
visible. FCB.
Fig. C. The broadened follicular wall of an oocyte of an allatectomized female, resorbed at
the end of previtellogenesis. Note several preserved small nuclei. FCB.
Fig. D. The resorption of oocytes in allatectomized females. The RNA-rich pycnotic material
from ooplasm (left) is transferred to the follicular epithelium as the process advances (right).
Toluidin blue.
Fig. E. The resorbed body overgrown by the interfollicular tissue and bordered by coherent
peritoneal epithelium. PARS.
Fig. F. The space between the resorbed body (right) and the peritoneal epithelium, filled by
loose fibrous material with free cells proliferating from the inner envelope. Una-Pappenheim.
6
PETR MASNER
individual oocytes are separated by interfollicular plugs. These tissues normally
differentiate from the prefollicular syncytium, but further differentiation of the
follicular cells, which should give rise to the secretory epithelium, never takes
place. The cells remain dormant. Their cytoplasm remains thin, and RNA is
found to stain densely only alongside the outer margin of the cells. The nuclei
show no progressive development, still retaining nearly the same character and
dimensions as those of prefollicular tissue and a volume of 15/t3. They are
invariably situated alongside the outer margin of the epithelium, occupying no
more than a quarter of the total volume of cells. The nuclear chromatin is thin,
with faint granules scattered at the nuclear membrane. Amitotic division and
binucleate cell formation have never been observed. The cells remain connected
one with another and the interfollicular spaces do not develop (Plate 2, fig. B;
Text-fig. 1)
Consequently vitellogenesis never takes place and the oocytes deteriorate after
the supply of nutrients from the trophocytes ceases. The germinal vesicle dis*
integrates and vacuoles appear in theooplasm.The rest of the ooplasm gradually
condenses into a mass rich in RNA and quite Feulgen-negative. The massive
plasmatic centre is surrounded by a thin, fibrous, slightly acidophilic material.
The mass gradually breaks down and the content of RNA decreases. Simultaneously, RNA-rich material passes through the disintegrating follicular epithelium (Plate 2, fig. D). Finally the entire contents of the oocyte are exhausted
and only slightly RNA-positive residues remain.
The follicular epithelium disintegrates simultaneously with its oocyte. The
epithelium swells up and is about 4 times thicker in the advanced period of
resorption. The cell boundaries disappear and numerous toluidin blue-positive
droplets of different size, digestible by RNAase, pass through from the ooplasm.
They are mostly located at the inner margin, but disappear later on. The nuclei
become pycnotic and disintegrate gradually. Feulgen-positive material is rare
in comparison with the follicles emptied after ovulation. Several living nuclei
may still be found among the debris of the epithelium. These show no apparent
changes which could suggest an active role in the process of oosorption. They
still retain the original perichromocentrical nuclear type and size—volume, 16 /A3
(Plate 2, fig. C; Text-fig. 1). Neither mitotic nor amitotic divisions have ever
been observed. Similarly no proliferation or lecitolytic cell formations have
been found.
The residues of both oocyte and follicle are intermingled and condensed into a
formation resembling the corpus luteum. But unlike the latter, the resorptive
body is never pushed into the pedicel. These bodies remain as individual units in
the vitellarium and are finally overgrown by the tissue of the interfollicular
plugs, which are still in good condition (Plate 2, fig. E).
The material from the resorbed oocyte, passing from ooplasm to follicular
epithelium and later disappearing, seems to pass to the space between the
resorptive body and peritoneal epithelium. It is filled up by a thin, fibrous,
Follicular differentiation
1
slightly acidophilic mass. This material is negative both to RNA and DNA
acids, as is the residue remaining inside the oocyte after the ooplasm has been
exhausted. Numerous free cells are scattered in this material. They arise from
patches of cells located originally in the constricted regions between neighbouring oocytes. They represent the remnants of the second sheath of each ovariole,
the inner envelope, which disappears in the mature ovary. These cells do not
seem to play an important role in the transport of the resorbed material. Their
nuclei are spherical, small, and perichromocentrical (Plate 2, fig. F). The fibrous
material probably penetrates through the thin peritoneal epithelium to the
haemolymph.
DISCUSSION
The process of oogenesis depends upon the activity of two ovarian nutritive
systems: the trophocytes, which are differentiated in larval stages, and an active
follicular epithelium, the differentiation of which takes place throughout
imaginal life. The prefollicular syncytium situated at the base of the vitellarium
is the only undifferentiated tissue of the adult ovary. It still retains its larval
character. The differentiation of the prefollicular syncytium is a process during
which the regular follicular epithelium on one hand and the tissue of the interfollicular plug on the other hand originate by intercellular differentiation (in the
sense of Spratt, 1964). This transformation continues by intracellular differentiation of follicular epithelium resulting in formation of the specialized secretory
•epithelium. The latter process is final; the tissue produced is very stable and its
cells have no possibility of further progressive development.
What are the inductors of these differentiation processes? The first step, the
differentiation of prefollicular tissue, characterized by the cell wall formation,
does not depend upon endocrine control. The true inductor of this process is
probably the activated oocyte itself, growing at the expense of trophocytes into
the prefollicular tissue. This is a case of cellular interaction and the intercellular
differentiation results in the formation of two types of tissues, follicular and
interfollicular. This differentiation seems to be determined by the different
micro-environment of the responding cells. The follicular cells are exposed to
the pressure exerted by the surface of the oocyte, and the interfollicular plug is
contracted between two growing oocytes (Masner, 1966). In other words, the
transformation of the prefollicular tissue seems to be a response to the changes
caused by the growing oocyte. The tissue is stretched and its nuclei separated.
This resembles the activation of fat body cells described by Wigglesworth (1964)
in Rhodnius, where, however, nutrition is another necessary inducing factor
beside the stretching of the tissue. Cell membrane formation is characteristic
of this process, but the cells retain relatively great developmental capacity. The
mitotic figures, which are still present, can be viewed as evidence of low specialization. Differentiating follicle cells multiply frequently, as observed by King &
Koch (1963) in Drosophila where each cell from the very young follicle is
8
PETR MASNER
said to divide four times before the definitive number of follicle cells is
reached.
Further development of the oocyte in the period of vitellogenesis requires
further differentiation of the follicular epithelium. This process, often called
activation, begins during previtellogenesis. The follicular cells develop subsequently into active secretory cells and tremendous growth and later amitotic
division of nuclei characterize this transformation (Masner, 1965). The tendency
of the follicle cells to undergo endopolyploidy has been demonstrated by
Durand (1955) and Schultz (1956). The differentiated follicle cells may contain,
according to the latter author, 8-16 times the haploid amount of DNA.
The feeding of the insect, and the concentration of nutrients in the blood, does
not have a direct influence on these cells. A comparatively high concentration of
proteins and free amino acids has been found in the haemolymph of allatectomized females in many insects (L'Helias, 1953; Highnam et al. 1963), among
them Pyrrhocoris apterus (Slama, 1964 a). These nutrients are not, however,
used for yolk formation in the absence of JH, when the follicular cells remain in
a dormant stage, characterized by small nuclei located alongside the outer
margin of the mononuclear cells.
The JH appears to be the activator of the follicular cells (Wigglesworth, 1936).
This was proved by Novak, Slama & Wenig (1959) and Johansson (1955, 1958),
who succeeded in activating the ovaries by active corpora allata, even in starved
females. The direct effect of the AH from the median neurosecretory cells has
been reported in this connexion in several insects (Thomsen, 1948,1952; Gillett,
1955; Girardie, 1963; Wigglesworth, 1965a, b). In Pyrrhocoris Slama (1964a)
concluded, in agreement with many authors working on other insects, that AH
regulates only digestive metabolism, whereas JH regulates the reproductive
metabolism.
The decisive role of JH in follicle activation has been confirmed in the present
study by the finding of the same histological picture of the ovaries in allatectomized as well as cardiac-allatectomized females. Highnam et al. (1963) ascertained that in Schistocerca the neurosceretory system ceases to release AH
within 4 days after allactomy. In Pyrrhocoris, nevertheless, there is reason to
assume that AH is still present in the haemolymph even in 15-day-old females,
such as those used in the present study. Slama (1964a) found a markedly higher
oxygen consumption in allatectomized females as compared with that of cardiacallatectomized ones, in 15-day-old material. The AH-controlled digestive
metabolism is responsible for increased oxygen consumption.
It seems strange that JH appears to induce differentiation of the follicular
epithelium of adults yet inhibits morphogenesis of the larval epidermal tissues.
This has already been observed by Telfer (1965), who found a hormone indistinguishable from JH to be activator of the final stages of oocyte development.
The suggested existence of two different corpus allatum hormones—in larvae
(neotenin) and in adults (gonadotropin)—proposed by Luscher & Springhetti
Follicular differentiation
9
(1960) and Sagesser (1960) does not seem to be satisfactory. That a single
hormone causes both actions, first suggested by Wigglesworth (1935,1948,1954)
and Pfeiffer (1945) has been proved (Novak & Slama, 1962; Slama & Hrubesova,
1963; Slama, 1964a) and is now accepted by most authors.
The concentration of the hormone, however, is probably different in each
case and the character of the responding cells is also diverse, and, perhaps, the
conditions under which the JH acts in larvae and adults are completely different. A final proof that different combinations of simple environmental components could elicit different gene activity patterns would be extremely important
(Spratt, 1964). Ecdysone could serve as an example. It is shown by Clever (1965)
to induce different processes in different tissues. Furthermore, the reaction to
ecdysone is different at different stages of development.
It may be concluded that JH, which inhibits differentiation in larval development, is able to act as an inductor of differentiation of follicular cells in adults.
The effect of JH on suppression of differentiation in larvae, however, has been
largely based on observations of the epidermal cells. When the imaginal rudiments of inner organs are taken into consideration, the role of JH appears in
new light. The example of a gradual differential growth of ovarian imaginal
disks during the postembryonic period in Oncopeltus was presented by Wick &
Bonhag (1955); the presence of active JH does not interfere with the transformations described. The role of JH in ovarian development in adults appears
to be a part of gradual development of the organ. It follows that a striking
difference in the action of JH during ovarian organogenesis would not be
expected. Novak (1967), in his criticisms of the general validity of Williams's
(1961) antiderepression hypothesis of JH action, pointed out that the mechanism
of morphogenesis is not only determined in the genetic sense but is largely a
result of a complex interaction also involving the intraenvironment (i.e. microenvironment). It follows that the same effector—JH—which suppresses indirectly
the differentiation of the larval body does not necessaily interfere with the differential growth of its specific parts; for example, the ovarian tissues of the
larva. It seems that JH might also be viewed as an inductor of differentiation in
the foliicular epithelium in the ovaries of adults.
The oocytes of allatectomized as well as cardiac-allatectomized females
deteriorate after they have completed previtellogenesis. The active role of the
follicular cells, invading the ooplasm, was described by Wigglesworth (1936)
in Rhodnius. A similar feature has often been described in insects, and the
proliferation of the cells (lecitolytic cells after Lusis, 1963) has been demonstrated in the oocytes at the beginning of vitellogenesis (Palm, 1948; Lusis,
1963; Davis, 1964; Masner, 1966). The degeneration of oocytes stopped during
previtellogenesis, however, is often delayed (King, Rubinson & Smith, 1956;
Highnam, 1964). The resorption of theoocytesin allatectomized females has been
described in many insects (de Wilde & Boer, 1961). Oosorption in Pyrrhocoris
under these conditions is described in the present study. Invading cells were
10
PETR MASNER
never observed inside the oocyte surrounded by the dormant cells. These do
not take an active role in the transmission of the material from haemolymph
into the ooplasm and may also be incapable of transmitting in the opposite
direction (Masner, 1965). The material of the degenerated oocyte disintegrates,
presumably in consequence of autolysis, and passes through the decomposed
follicular wall.
Prabhu, Ittycheria & Nayar (1967) have observed some loose material
originating from resorbed oocytesfillingup the space between the resorptive body
and peritoneal epithelium in Iphita limbata. It was suggested that the free cells
described in this region are proliferated from the tissue of the terminal filament
and participate actively in the oosorption. This explanation of both the function
and origin of these cells, found also in Pyrrhocoris, seems to be questionable.
SUMMARY
1. The oocytes of the telotrophic ovarioles of Pyrrhocoris apterus are
nourished by two nutritive systems: the trophocytes, already differentiated in
newly emerged adults, and the follicular epithelium, which must first differentiate from the prefollicular syncytium.
2. This differentiation passes through two periods, induced by two different
inductors.
3. The first process is induced by the activated oocyte as it grows into the
prefollicular syncytium, which is transformed by intercellular differentiation
into the regular follicular epithelium on the one hand, and interfollicular tissue
on the other.
4. The second process is induced by JH. The follicular epithelium is transformed by intracellular differentiation into a specialized secretory epithelium.
The interfollicular tissue does not change during this period.
5. The growth and amitotic division of the nuclei of the follicular cells is a
most sensitive indicator, registering the smallest traces of JH in the blood, long
before the first yolk granules appear in the ooplasm.
6. In the absence of JH the follicular cells remain dormant, taking no active
role in the transport of the material from the blood to ooplasm and in the
opposite direction. The material of the degenerated oocytes penetrates simply
through the disintegrating follicular epithelium.
7. The resorptive body is overgrown by the interfollicular tissue, which still
retains a great developmental capacity.
8. The free cells found in the material between the resorptive body and peritoneal epithelium originate from the isolated cellular patches of the tissue of the
inner envelope, arising in the larval ovarioles.
Follicular differentiation
11
RESUME
Les inducteurs de la differentiation du tissu prefolliculaire et Vepithelium folliculaire dans les ovarioles de Pyrrhocoris apterus (Heteropterd)
1. Les oocytes des ovarioles telotrophiques de Pyrrhocoris apterus sont
alimentes par deux systemes nutritifs, les trophocytes, deja differencies chez les
adultes nouvellement formes, et Pepithelium folliculaire qui doit se differencier a
partir du syncytium prefolliculaire avant son entree en fonctions.
2. Cette differentiation passe par deux periodes, induites par deux inducteurs
differents.
3. Le premier processus est induit par l'oocyte active quand il s'accroit dans le
syncytium prefolliculaire, qui se transforme, par differentiation intercellulaire,
en epithelium folliculaire regulier d'une part, en tissue interfolliculaire d'autre
part.
4. Le deuxieme processus est induit par l'hormone juvenile (JH). L'epithelium folliculaire se transforme, par differentiation intracellulaire, en un
epithelium secretaire specialise. Le tissue interfolliculaire ne se modifie pas
durant cette periode.
5. La croissance et la division amitotique des noyaux des cellules folliculaires
constituent l'indicateur le plus sensible enregistrant les plus faibles traces d'hormone juvenile dans le sang, longtemps avant l'apparition des premiers granules
de vitellus dans l'ooplasme.
6. En l'absence de JH, les cellules folliculaires restent dormantes, ne prenant
pas de part active au transport de materiaux du sang a l'ooplasme et dans la
direction opposee. Le materiel des oocytes degeneres penetre simplement a
travers l'epithelium folliculaire en disintegration.
7. Le corps de resorption est recouvert par le tissue interfolliculaire, qui conserve encore de grandes capacites de developpement.
8. Les cellules libres trouvees dans le materiel entre le corps de resorption et
l'epithelium peritoneal proviennent des groupes de cellules isoles du tissue de
Penveloppe interne, trouvee dans les ovarioles larvaires.
The author is indebted to Dr K. Slama for the operated females supplied for this study and
for kind comments during the work, to Dr V. Landa, Dr V. J. A. Novak and Sir Vincent B.
Wigglesworth for valuable criticism of the manuscript.
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{Manuscript received 17 October 1967)