Recent Advances in Insect Embryology in Japan and Poland
Edited by H. Ando and Cz. Jura
Arthropod. EmbryoL. Soc. Jpn.
(lSEBU Co. Ltd., Tsukuba) 1987

51

Inductive Effect of Oocyte Nucleus
on Ovarian F oBicle Morphogenesis
in Water Bugs (Heteroptera)

Antoni OGORZALEK
SynopsisUsing electron (TEM, SEM), polarization and fluorescence microscopies oogenesis in following water bugs was studied: Notonecta glauca, Jlyocoris cimicoides, Ranatra linearis,Nepa cinerea andCorixa punctata. The aim of the study was to analyse factors causing a diversification of the uniform prefollicular cell population into subpopulations of different morphology and function. The
results indicate that the inductive effect of the oocyte nucleus is one of such factors determining
the morphogenesis and biology of ovarian follicles in the studied species. The "compartmentation" of the previtellogenic ovarian follicles causes a temporal and spatial differences in the exposition of the follicular cells to this factor. This brings about a functional discoordination of theepithelium which subsequently determines the deutoplasm distribution and the egg capsuleformation.

Introduction
Egg capsule (chorion) of bugs are often provided with adaptive structures which
serve to fasten the eggs to or inside plants and enable gas exchange between embryoand environment (Hinton, 1981). These structures are formed by modified follicular
cells. Observations on the interdependence between the oocyte nucleus position, therange of the trophic cord penetration in ovarian follicles in previtellogenesis and theepithelium deversification during vitellogenesis and choriogenesis, in eight bug species(Notonecta glauca, /lyocoris cimicoides, Ranatra linearis, Nepa cinerea, Corixa punctata, Gerrislacustris, Pyrrhocoris apterus and Lygaeus equestris) suggest that the oocyte nucleus is an inductor of the follicular cell differentiation (Ogorzalek, 1969, 1974, 1975a, b, 1984, inpress). The results of new studies on this interdependences are presented in this paper.

52

A. Ogorzalek

Material and Methods
Females of Notonecta glauca, Ilyocoris cimicoides, Nepa cinerea, Ranatra linearis and Corixa punctata (imagines and last instar larvae) were collected in the spring and summer
1983, 1984 and 1985 in the clay pits near Wrodaw (Lower Silesia). Ovaries were dissected in Ringer solution for Drosophila and fixed in Carnoy's (6: 3: 1) fixative, 5 % formaldehyde in 0.1 M phosphate buffer, pH 7.4 and in 5 % glutaraldehyde in the same
buffer. Sections were stained using the panoptic method according to Pappenheim andwith methylene blue and borax, ultrathin sections were stained with uranyl acetate andlead citrate. Observations were made in fluorescence microscope Ljuman L-l, polarization-interference microscope MPI-3 (PZO Warsaw), TEM Tesla BS-6l3 and SEM
Tesla BS-300. The material for SEM studies, prior to fixation, was placed in distilledwater. Following the osmotic disintegration of the epithelia, their remnants were removed and the egg capsules at various chorionogenesis stages were repeatedly rinsed in
distilled water. After the fixation, postfixation and dehydration in alcohol series andacetone the material was dried and coated with carbon and gold.

Results
I. Ovary structure

The general ovary structure in the studied species resembles that of the other
Heteroptera (for review see King and Buning, 1985). The oocyte growth in the ovarioles is asynchronous while in all the species except C. punctata there is a horizontal interovariole synchronization. The analysis of various portions of ovarioles indicates interspecific differences in the process of the ovarian follicle formation, growth and differentiation: the differences consist in unequal time of differentiation of various parts ofthe epithelium as well as in the range of the diversification.

A. Primary diversification of the follicular epithelium
The diversification of the originally homogeneous group of prefollicular (stem)
cells into two subpopulations takes place at the moment of the ovarian follicle formation in the meristematic portion of the ovariole, in all species according to a similar
scheme. A part of the cells assume a lateral localization relative to the oocyte and contact with the ovariole wall, others are localized between the oocytes in the paraaxial
ovariole portion with no direct contact with haemolymph. The former group, in thefurther course of the oogenesis, forms a high prismatic epithelium built of binucleatedcells, and surrounding cylindrically the proximal ovariole portions. The latter group, asa rule mononuclear, form interfollicular septa, still without a contact with the epithelium basal membrane (Fig. 16). Consecutive endomitoses that increase the follicularcell ploidy (in I. cimicoides to 32n, Ogorzalek, 1978) initially occur in the prismatic portion of the epithelium which leads to a quick diversity in size of both cell types. The
cytoplasm of the interoocyte septum cells shows a higher affinity to basic stains whichOvarian follicle morphogenesis in water bugs

53

Ilyocoris cimicoides. Tropharium (Tr) and proximal part of vitellarium (Vit) viewed
in polarization microscope. Trophic core (TCo) and trophic cord (TCd) lighten.
Scale: ca. 150 pm.
Fig. 2. Ilyocoris cimicoides. Previtellogenic ovarian follicle. Structures causing a rotation ofpolarization plane penetrate proximal part of follicle (TCT). PO, proper ooplasm.
Scale: ca. 150 pm.
Fig. 3. Ilyocoris cimicoides. Early vitellogenic ovarian follicle. Lighter territory in proximal
part of follicle (TCT) asymmetrical. PO, proper ooplasm. Scale: ca. 170 pm.
Fig. 4. Notonecta glauca. Previtellogenic ovarian follicle. Trophic cord (TCo) only slightly
penetrates into the ovarian follicle (arrow). Scale: ca. 150 pm.
Fig. l.

allows a good distinction between them and the remaining epithelium cells. At thestage of budding of elliptical ovarian follicles off the end of the cylindricll ovariole portion, the septum cells undergo a reorganization and form a "casing" of the trophic cordoutlets to ovarian follicles, and interfollicular stalks (Figs. 7, 18, s-cells). This process isaccompanied by mitotic divisions which by that time have already stopped in the remaining part of the epithelium. This arrangement persists until the end of vitellogenesis and in the chorionogenesis the s-cells build the micropylar apparatus.

B. "Compartmentation" of the ovarian follicle content
At the end of the previtellogenesis in the studied species (except N. cinerea and R.

54

A. Ogorzalek

linearis) a division of the ovarian follicle content into two territories ( "compartments" )takes place. Their apical portions are penetrated by the trophic cords and thus thetrophic cord area can be distinguished, as well as the area of the "proper" ooplasm
containing the oocyte nucleus.
1. Studies in polarization microscope
A great number of parallelly arranged microtubules results in the trophic core area
and the trophic cord area in bug ovarioles causing a rotation of the polarization planeand both these structures are easily revealed in polarization microscope (Stebbings,
1971). This allows to determine the penetration range of the trophic cords inside theovarian follicles (Figs. 1 - 4). The range of the trophic cord viewed in polarization
microscope in greatest in I. cimicoides. The rotation of the polarization plane in this species comprises apical portions of the previtellogenetic and early vitellogenetic ovarianfollicles, the outline of the trophic cord area being already asymmetrical (Fig. 3). In R.
linearis and N. cinerea the area of the arranged microtubules reaches the level of apicalportions of the cell adjoining the trophic cord outlet or in Not. glauca (Fig. 4) slightly
exceeds this zone. In C. punctata (Fig. 21) an intermediate condition is observed namely
the arranged microtubules penetrate the follicle but the area occupied by them andtheir density are smaller than in I. cimicoides.
2. TEM studies of Ilyocoris cimicoides
In I. cimicoides the "transit" trophic cords running inside the follicular epitheliumof the previtellogenic and early vitellogenic ovarian follicles have a round smooth outline in transverse section, and there is a close contact between the trophic cord membrane and the follicular cell membrane. Only sporadically on small areas systems ofshort, flatly arranged and overlapping microvilli are observed which on transverse section in electron microscope appear as rows of round or oval, adjoining outlines.
Microtubules, arranged parallelly to long axes of the trophic cords and ribosomes,
are rather evenly distributed in the trophic cords. Mitochondria, fine and filled withelectron dense matrix, lie peripherally. In the proximal portion of the trophic cord
territory, already inside the follicle, the microtubules are still arranged parallelly andrather regularly (Figs. 5, 5 a). In the distal portion the paracentral bundles of microtubules take a wave-like course of increasing amplitude, while the direction of theperipheral microtubules changes from the parallel to the epithelium surface to the centripetal, also wavy. Beside the fine mitochondria already mentioned, in the distal portion of the trophic cord territory, much larger ones, also peripherally situated areobserved. They are of discoidal shape and lie parallelly to the epithelium surface.
In spite of the lack of any border structure, the border between the trophic cord
territory and the proper ooplasm is relatively distinct. No syntopy of the ooplasm richin microtubule bundles and ribosomes, and the deutoplasmic elements was observed.
Also the large number of mitochondria in the proper ooplasm, and their almost total
absence in the intrafollicular area of the trophic cord are good criteria distinguishingOvarian follicle morphogenesis in water bugs

55

Figs. 5, 5 a. Ilyocoris cimicoides. Proximal part of early previtellogenic ovarian follicle. TEM.
Follicular cells (FC), trophic cord territory (TCT) with micro tubules and ribosomes. Border TCT-follicular cells smooth. Scales: ca. IS p m (Fig. 5), ca. 5 pm
(Fig. 5 a).
Figs. 6, 6 a. Ilyocoris cimicoides. Distal part of ovarian follicle, stage as on Fig. s. TEM.
Proper ooplasm (PO) rich in ribosomes and mitochondria. On border PO-follicular cells (FC) microvilli form. TTC, transverse section of "transit" trophic cord.
Scales: ca. IS pm (Fig. 6), ca. 6 pm (Fig. 6 a).

56

Fig. 7.

Fig. 8.

Fig. 9.

A. Ogorzalek

llyocoris cimicoides. "Closing" of columnar epithelium part in early previtellogenic
ovarian follicle. Follicle content divided into trophic cord territory (TCT) andproper ooplasm (PO). In cells originating from septum (se) mitoses visible. Scale:ca. 70 pm.
llyocoris cimicoides. Early vitellogenic ovarian follicle. Follicle content divided into
trophic cord territory (TCT) and proper ooplasm (PO) (broken line) . Epithelium
diversified into prismatic and low, deutoplasm gradient decreasing with the distance from the oocyte nucleus (ON). Scale: ca. 80 pm.
llyocoris cimicoides. Early vitellogenic ovarian follicle (later than of Fig. 8). Transverse section. Cells adjoining the oocyte nucleus (ON) decreased in height, nucleus
surface facing the epithelium concave. VS, yolk spheres . Scale: ca. 80 pm .

Ovarian follicle morphogenesis in water bugs

57

both territories (Figs. 6, 6 a).

c. Secondary diversification of follicular epithelium -retardation

The division of the ovarian follicle content into the trophic cord territory and theproper ooplasm takes place when the elliptical ovarian follicles are covered with a uniform high prismatic epithelium (Fig. 7). In the further oogenesis, the cells adjoining
the trophic cord area retain this original morphology and arrangement. Their nuclei
are situated above one another, their apical portions are flat and until the advanced
vitellogenesis they retain a rather close contact with the oolemma. Until the end of thechorionogenesis these cells adjoin each other (A-cells, Figs. 8, 10, 11).
The cells contacting with the proper ooplasm, beginning with the late previtellogenesis undergo a sequence of morphological changes typical of the bug vitellogenic
epithelium. They decrease in height and the epithelium becomes low- instead of highprismatic, and then iso-prismatic. The shape of the cells, initially polygonal, grows
more or less oval. At the end of this sequence of the differentiation changes the cells
move apart, their only contact being by cytoplasmic arms, and their apical portions
form bulb-like protrusions in the ooplasm. As the cells decrease in height and moveapart, their nuclei, initially situated above one another, arrange on a level. Their flattened surfaces facing each other at the end of the vitellogenesis undergo invagination
resulting in a cylindrical space of an internuclear cytoplasm, perpendicular to the ooplasm surface (B-cells).
The space between the follicular cells that have move apart is limited by theepthelium basal membrane at one side, and by the oolemma at the other. It is filledwith a material showing an affinity to eosin in panoptic staining according to Pappenheim. This makes it possible to use a patency index (Davey and Huebner, 1974) influorescence microscope (see Fig. 11). The index shows that the final distance between
B-cells varies between species and at the end of vitellogenesis it is in I. cimicoides morethan 5, in R. linearis, N. cinerea and Not. glauca ca. 3 and in C. punctata ca. 2.
With the advance of the vitellogenesis the trophic cord territory is gradually"pushed out" from the ovarian follicle. As a result, a part of the cells originally adjoining the trophic cord area enters (somewhat later than the other cell) in contact withthe proper ooplasm. During the advanced vitellogenesis they show a mixture of characters namely they are high prismatic, their nuclei lie above one another, the cells themselves being moved apart and connected by cytoplasmic arms and their apical portions
from bulb-like swellings (AB-cells).
Fig. 10. Ilyocoris cimicoides. Vitellogenic ovarian follicle. Transverse section. Oocyte nucleus(ON) situated on cumulus nucleophorus (en). A-, AB- and B-cells visible. Scale:ca. 150 p. m.
Fig. 11. Ilyocoris cimicoides. Vitellogenic ovarian follicle. Longitudinal section. Epithelium diversified into A-, AB- and B-cells. Fluorescence substance filling intercellularspaces allows a determination of the epithelium patency. Scale: ca. 90 p. m.
(Figs. 7 - 11; formaldehyde, paraffin sections, Pappenheim panoptic method, fluorescencemicroscope. )58

A. Ogorza!ek

Ilyocoris cimicoides. Apical part of ovarian follicle - chorion formation. Chorion
plate formed by A-cells is thicker, deeper sculptured and less eosinophilous thanthe other parts of egg capsule. MA, micropylar apparatus. Scale: ca. 40 pm.
Fig. 13. Ilyocoris cimicoides. Chorion plate in apical part of egg capsule. SEM. Deep prints ofA-cells apical portions, micropylar apparatus (MA) , chorion collar, covering thejunction between the plate and the rest of egg capsule, formed by AB-cells. Collar
visible also on Fig. 12 (arrow). Scale: ca. 65 pm.
Fig. 14. Ilyocoris cimicoides. Subapical part of ovarian follicle - chorion formation. B-type
follicular cells compact, chorion strongly eosinophilous, in outer capsule part pits. Scale: ca. 40 pm.
Fig. 15 . Ilyocoris cimicoides. Chorion in subapical part of egg capsule. SEM. Outer layer of
egg capsule perforated. Scale: ca. 12 pm.
(Figs. 12, 14; Carnoy, paraffin sections, Pappenheim panoptic method, fluorescence microscope. )Fig. 12.

D. Lateralization of the oocyte nucleus
During the previtellogenesis in all the studied species a migration of the nucleus
takes place from the paracentral portion of the oocyte to its periphery. The time of the
migration and the trajectory of the nucleus as well as its ultimate localization in theparaepithelial ooplasm are species-specific (see Fig. 27).
In Not. glauca and I. cimicoides the migration takes place at the time of closing of
the cylindrical part of the epithelium in the process of budding ofT of the ovarian folli-Ovarian follicle morphogenesis in water bugs

59

Fig. 16. Ranatra linearis. Fragment of germarium and proximal part of vitellarium. Oocyte
nuclei (ON) in consecutive follicles alternately arranged. Cells on contact epithelium - ON - hypertrophied (HFC) . Epithelium primary diversified into highprismatic and innerfollicular septum cells (ISC). Scale: ca. 60 p. m .
Figs. 17, 18. Late previtellogenic ovarian follicles in Ranatra linearis (Fig. 17) and Nepa
cinerea (Fig. 18). Epithelium diversified into super-B-, B- and (around trophic cordoutlet) s-cells (sc). Scales: ca. 120 p. m.
Fig. 19. Nepa cinerea. Proximal part of egg capsule. SEM. Respiratory horns formed by super-B-cells surround the "honeycomb" chorion plate. Scale: ca. 110 p. m .
Fig. 20. Nepa cinerea. Subapical part of egg capsule. SEM. Prints of follicular cells and filler
material accumulations visible. Scale: ca. 15 p. m.
(Figs. 16-18; semithin sections, metylene blue and borax. )60

Fig. 2l.

A. Ogorzalek

Corixa punctata. Previtellogenic ovarian follicle. Polarization microscope. Polarization-active structure penetrates the follicle (arrows). Scale: ca. 65 p. m.
Fig. 22. Corixa punctata. Late previtellogenic ovarian follicle. Oocyte nucleus (ON) moved
to distal part of the follicle. Follicle content divided into trophic cord territory andproper ooplasm (broken line). Scale: ca. 40 p. m.
Fig. 23. Corixa punctata. Early chorionogenic ovarian follicle. In epithelial pocket forming
chorion process (ChP) visible. Panoptic Pappenheim method, light micrtoscope.
Scale: ca. 140 p. m.
Fig. 24. Corixa punctata. Grown ovarian follicle. Polarization microscope. On proximal polemicropylar apparatus forms, on distal pole, in epithelial pocket adaptive chorion
structure visible. Scale: ca. 150 p. m.

Ovarian follicle morphogenesis in water bugs

61cles. The nucleus reaches the periphery in equatorial portion of the oocyte. In Not.
glauca it remains in this position till the end of vitellogenesis, in 1. cimicoides it migrates
farther, already in contact with the epithelium, to the subapical portion of the follicle,
its ultimate position being near the trophic cord outlet (Fig. 8). In C. punctata the migrating nucleus is situated first in the distal oocyte pole (Fig. 22). Then (at the end of
the previtellogenesis) the nucleus migrates ultimately to the posterio-lateral part of theoocyte. In R. linearis and N. cinerea the nucleus peripherization occurs in V larval stage
ovaries. The nucleus migration is preceded by a folding of the nuclear envelope on theside turned in the direction of the migration. In imaginal ovarioles, in the differentiatedovarian follicles, the nucleus assumes an extremely eccentrical position, at the opposite
side relative to the trophic cord outlet (Fig. 16).

E. Secondary diversification of the follicular epithelium -development acceleration
The process of the secondary diversification of the columnar epithelium part in R.
linearis and N. cinerea is opposite (negative) as compared with the retardation diversification described above. A group of cells (in R. linearis, 2; in N. cinerea, 6 - 7) which
already in the larval ovary has come to lie in the immediate vicinity of the oocyte nucleus starts growing faster than the other cells and differentiate into B-cells (Figs. 1618). Their shape becomes oval, the nuclei localize on one level and the apical parts
protrude to the ooplasm. Grains of the prechorional material appear in their cytoplasm
earlier than in the remaining epithelium cells (super-B-cells).
11. Vitellogenesis

In all species studied fluorescent, eosinophilous granules are first observed in thespace between the peripherally situated oocyte nucleus and the follicular epithelium.
The only exception is the vitellogenesis in R. linearis where first yolk spheres appear in
the ooplasm pocket adjoining the hypertrophic follicular cells, while at the same time
the remaining ooplasm is still of previtellogenic character. However, in advanced vitellogenesis, in both R. linearis and N. cinerea yolk spheres are observed in the space between the oocyte nucleus and the epithelium, the two territories of increased vitellogenic activity being separated.
In Not. glauca and 1. cimicoides the oocyte nucleus surface facing the epithelium invaginates at the beginning of the vitellogenesis. The resulting space between the nucleus and the epithelium has, in Not. glauca a lenticular shape, while in 1. cimicoides it isgutter-like, parallel to the follicle long axis, and widens proximally. In both the early

Corixa punctata. Adaptive chorion structure on distal pole of egg capsule. Thick,deeply sculptured chorion plate formed by prismatic cells of epithelial pocket(FEP) visible. Scale: ca. 40 fL m.
Fig. 26. Corixa punctata. Proximal part of the egg capsule. SEM. Homogeneous chorion surface formed by B-cells and micropylar apparatus (MA) visible. Scale: ca. 90 fL m.
(Figs. 22, 25; Carnoy, paraffin sections, Pappenheim panoptic method, fluorescence microscope. )Fig. 25.

62

A. Ogorzalek

and the advanced vitellogenesis the yolk spheres in this space (and in I. cimicoides on its
prolongation as well) are many times larger than in the remaining ooplasm (Fig. 9). In
the advanced vitellogenesis, in all the species, a gradient of vitellogenic activity isobserved, the activity decreasing gradually with the increasing distance from the oocyte
nucleus. This results in an early asymmetry of the oocytes because of the deutoplasm
distribution.

Ill. Morphological modiftcations of the epithelium related to the neighbourhood of the oocyte nucleus
In Not. glauca and I. cimicoides follicular cells situated in the nearest vicinity of theoocyte nucleus, decrease in height forming in vetellogenesis a pit, bordered by a groupof cells higher than in the remaining part of the epithelium. In I. cimicoides the phenomenon if accompanied by a nuclearward arrangement of the apical parts of the cells,
which on tangential sections gives local radial patterns. In this species, at the end of
the vitellogenesis the oocyte nucleus, with its surface facing the epithelium strongly
folded because of the pressure exerted by yolk spheres, migrates and adjoins closely theepithelium. At the contact the cells grow higher than the surrounding ones and a"cumulus nucleophorus" arises on which the nucleus forms a characteristic cap (Figs.
10, 11).
A different reaction of the epithelium to the neighbourhood of the oocyte nucleus
takes place in C. punctata where on the distal oocyte pole, at the first contact epithelium-nucleus, a pit forms and then an epithelial pocket (Figs. 23, 24). Morphologicalchanges in the cells surrounding this separated ooplasm fragment in the pre- and theearly vitellogenesis are synchronous with the changes in the remaining epithelium part,though the space bordered by them is devoid of yolk. At the end of the vitellogenesis
the pocket undergoes flattening and the cells that form its distal part become high prismatic. They enter the chorionogenesis earlier than the remining part of the epithelium(Figs. 23,.25).

IV. Chorionogenesis
The egg capsule formation is preceded by a reorganization of the follicular epithelium. The B-type epithelium gets flat and its patency disappears. The nuclei, situatedat one level, often change their position and arrange above one another or in such a
way that the axis connecting their centres is oblique relative to the oocyte surface. In I.
cimicoides the process of "closing" of intercellular spaces begins in the vicinity of the
cumulus nucleophorus and encompasses first AB-cells, and then B-cells.
The chorion produced by the high prismatic cells (plate on the proximal pole ofthe egg capsule in I. cimicoides - Figs. 12, 13; chorion plate between the respiratory
horns in N. cinerea- Fig. 19; distal part of the discoidal chorion process in C. punctataFig. 25) is always thick, deeply sculptured and azurophilous, which results in its
fluorescence on sections stained with Pappenheim's method being lower than the remaining part of the egg capsule. The chorion formed by the B-cells is thinner and on
its surface prints of apical portions of the follicular cells are visible. It can be covered

Ovarian follicle morphogenesis in water bugs

63with pits (I. cimicoides-Figs. 14, 15), accumulations of filler material (N. cinerea-Fig.
20) or uniformly smooth (C. punctata - Fig. 26). The super-B-cells form respiratory
horns in the proximal portion of the egg capsule (N. cinerea-Fig. 19).

Discussion
I. Diversification of the follicular epithelium in bugs
A. Morphology
The polymorphism of the follicular cells within the ovarian follicle in bugs connected with the formation of egg capsule respiratory horns ( "Atmungsschlauche" )was described in N. cinerea and R. linearis by Korschelt (1884, 1885, 1887, 1891) andKorschelt and Heider (1902). Gross (1901) described the presence of various morphological types of follicular cells in bugs and the part of the modified cells play in formation of various chorion appendages. Huebner and Anderson (1972) when studying thefine structure of the follicular cells in Rhodnius prolixus, found that the epithelium on theproximal pole of the follicles is compact and high prismatic. Further results (Anderson,1974) showed that the prismatic epithelial cells (A-cells) produce the deeply sculptured
cover of the egg capsule, similar in structure to the honeycomb. Studies of Huebner(1981) and Huebner and Injeyan (1981) show that in the ovarian follicles in Rho. prolixus gap junctions are present both between the follicular cells themselves, and between the follicular cells and the oocyte. Studies of Woodruff and Anderson (1984) on
small milkweed bug Oncopeltus fasciatus indicate a spatial differentiation of the distribution of fluorochromes injected into the ooplasm in various epithelium parts. This evidences the heterogeneous pattern of distribution of the above mentioned gap junctionsin the pre- and early vitellogenic ovarian follicles.

B. Mechanism
Experimental studies showed that the juvenile hormone OH) is responsible for the
regulation of the morphogenesis of the follicular cells in Rho. prolixus (Pratt and Davey,1972). The increasing distance between the epithelium cells which can be expressed as
patency index, is in vitro a function of the JH concentration in the medium (Davey andHuebner, 1974). The reaction of the follicular cells to the effective titer of JH ischanges in cytoskeleton (Abu-Hakima and Davey, 1977) and shrinking of the cells
caused by loss of water (Abu-Hakima and Davey, 1979). As a result of these changes
the shape of the follicular cells changes from prismatic, determined by mechanicaleffect of neighbouring cells into oval, with additional protrusions directed to the ooplasm. The cells move apart contacting by cytoplasmic arms. On place of their contact
septate and gap junctions are observed (Huebner, 1981, Huebner and Injeyan, 1981).
The sequence of morphological changes of the follicular cells, identical in all the
species described in the present paper, allows a supposition that the mechanism of thefollicular epithelium differentiation is similar in most bugs. The transformation of theA. Ogorzaiek

64

TYPE NEPA

'"

iii
III

Z
III

g

....
....

...

III

:;
III

f

l'lS!i- Trophic

cord territory

L'S::] - Proper ooplasm•_ Oocyte nucleus

f;J93 ---[ill] - s -DID - A - cells
IIlII - AB .- cells

Yolk spheres

1JlliIlll-B-celll

ChorionlIB - superB-'_ _ Oocyte
us traleCrOry

Fig. 27. Diagram showing four basic morphogenesis types in ovaries of water bugs parison.
1, morphogenesis type; 2, stage of oocyte growth.

com-Ovarian follicle morphogenesis in water bugs

65

chaotic, blastic mass of the prefollicular cells into the epithelium also requires (in Pyrrhocoris apterus) the presence of JH in haemolymph (Masner, 1968).

II. Asynchrony offollicular cellsdifJerentiation
When analyzing consecutive stages of the oocyte growth in the ovaries of each species, it can be stated that both the interovariole asynchrony (within an ovariole previtellogenic, vitellogenic and chorionogenic follicles may occur simultaneously) and thedevelopement epithelium discoordination within a follicle occurs. The original cause of
the discoordination phenomena (A-cells retardation, super-B-cells acceleration andhypertrophy) lies in temporal differences in the differentiation processes in various
epithelium parts. Assuming that all the follicles are equally exposed to the factors containing in haemolymph (see Riddiford, 1985, Epilogue) it can be supposed that theovarian follicles in the species studied show a considerable autonomy. The autonomy of
the ovarian follicles (egg chambers) in Bombyx mori was postulated by Legay (1979), inbugs by Ogorzafek (1975b). The results of the present study shows, though indirectly,that in the studied species the asynchrony and the discoordination can be reduced tothe statement that the trigerring and the possible interruption of the above differentiation mechanism in follicular cells are generated in the follicles themselves.

III. Bug ovarian follicle as an inductive system
The morphological analysis of the interdependence between the compartmentaionof the ovarian follicle content in consecutive oogenesis stages, the oocyte nucleus translocalization and the morpho-functional diversification of the follicular epithelium makes
it possible to regard the ovarian follicle as an inductive system. According to the handbook definition such a system consists of two components: an active one (inductor) anda reactive one. The retardation diversification of the epithelium in which the cell differentiation depends on their contacts with the proper ooplasm (cells with no such contact do not differentiate and retain ancestral characters) roughly point out to the oocyte
as an active component and to the follicular epithelium as a reactive one. The acceleration differentiation, as well as the later, local modification of the epithelium connectedwith the neighbourhood of the oocyte nucleus indicate that the oocyte nucleus is theactual inductor in the ovarian follicle morphogenesis in the studied species. Purely
morphological character of the present results and the indirect reasoning do not allow
for a definition of the mechanism of the described interaction. It enables only a construction of a simple model of the ovarian follicle morphogenesis in bugs.

IV. The morphogenesis model
The proposed model is based on a hypothetical assumption that the oocyte nucleus emits a factor (evocator ?, morphogene ?) which initiates the follicular cell differentiation. The chemical nature of this factor is unknown. If the gap junctions are the66

A. Ogorzalek

only physical canal through which it could penetrate to the follicular cells, the upper
limit of its molecular weight will be below 1,500: In the proposed model the factor iscalled FCDF (follicle cell differentiating factor) according to its postulated function and
it is assumed that the time of the emission depends on the oogenesis stage.
The sequence of events described above, which leads to the increase in epithelium
patency is a reaction of the follicular cells on FCDF (requiring an effective titer of JH
in haemolymph). When the oocyte reaches the threshold size, the differentiation program is stopped in all the cells at the same time, irrespective of which part of it has
been effected, and the cells synchronously start building the chorion.
The compartmentation of the ovarian follicle content results, in turn, in the asynchronous (and probably uneven) exposition of the cells to JH (primary epithelium diversification depending on the contact vs. lack of contact with heaemolymph) and to
FCDF (secondary differentiation of the epithelium, both retardation and acceleration).
The discoordination "relief" diversification of the epithelium determines the rough morphology of the egg. The high prismatic nature of the juvenile cells (A-cells) and the decrease in height of the cells in the remaining parts of the epithelium cause the modified
inner outline of the epithelium on the proximal egg pole, modelling the oocyte shape,
while the outer outline of the follicle remains unchanged.
If the postulated hypothesis on the inductive, morphogenetic role of the oocyte
nucleus in functioning and formation of bug ovarian follicle is accepted, thehaemolymph with its chemical milieu can be regarded as an environment interferingwith the processes that take place in the growing oocyte, albeit with no effect on thespatial diversification of eggs and their capsules. In this connection follicular cells
would be a "mediator" between the genetic and epigenetic system of the primaryoocytes on one hand, and the insect internal environment on the other. Their behaviour can be regarded as a resultant of the reaction to the environment factors (hormonal signals, yolk precursors or nutritive materials) and the signals coming from theoocyte itself (most probably its nucleus). Due to the latter signals in the spatiallyhomogeneous internal environment of the insects, morphogenetic processes in the ovarian follicles take place, resulting in the species-specific egg morphology in bugs.

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Author's address: Dr. A. Ogorzalek
Department of General Zoology, Institute of Zoology, Wrodaw University, ul. Sienkiewicza 21, 50-335
Wroclaw, Poland