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Ultrastructural studies on accessory nuclei in developing oocytes of the crustacean, Siphonophanes grubei
TISSUE AND CELL, 1991 23 (6) 903-907 0 1991 Longman Group UK Ltd.
J. KUBRAKIEWICZ”,
R. T. ADAMSKI”
and S. M. BlLlkSKlt
ULTRASTRUCTURAL STUDIES ON ACCESSORY NUCLEI IN DEVELOPING OOCYTES OF THE CRUSTACEAN, SIPHONOPHANES GRlJBEl Keywords:
Accessory
nuclei, oogenesis,
Crustacea
ABSTRACT. Numerous accessory nuclei (AN) occur within peripheral cytoplasm of Siphonophmes grubei oocytes. They exhibit typical nuclear structure, with double membrane envelope pierced by pore complexes. Although no explicit evidence was shown, indirect arguments exist indicating that AN originate from the oocyte nucleus. Presence of clumps of DNP material within AN suggests that AN might play some role in amplified DNA metabolism. Participation of AN in cellular membrane elaboration is also postulated.
Introduction
we report ultrastructural and histochemical investigations on AN in another representative of Phyllopoda, Siphonophanes grubei (Dybowski).
Accessory nuclei have been found in oocytes and embryonic cells of various arthropods (Hopkins, 1964; King and Fordy, 1970; Zissler and Sander, 1977; Meyer et al., 1979; Bilihski, 1989, 1991; Kubrakiewicz, 1991) and nematodes (Goldstein, 1981). These peculiar organelles are surrounded by double membrane envelope pierced by nuclear pores and contain electron dense inclusions termed ‘pseudonucleoli’. Additionally, it has been shown, that ‘pseudonucleoli’ are RNA-positive (Meyer et al., 1979). According to King and Fordy (1970), Meyer et al. (1979), Bilifiski (1989, 1991) AN originate from the oocyte nucleus and usually migrate to the peripheral ooplasm, where they persist till late oogenesis. Although the oogenesis of entomostracan crustaceans has been the subject of numerous ultrastructural investigations, the presence of AN has been reported only in the phyllopod, Artemia salina (Criel, 1989). Since the formation and/or function of the AN have not been fully explained, in the present paper
Material and Methods Females of Siphonophanes grubei (Dybowski) were collected from small, astatic water bodies near Wroclaw, Poland. Histological procedure
The ovaries were dissected and fixed in ethanol:acetic acid (3:l). Paraffin sections (6 pm thick) were stained with May-GrunwaldGiemsa according to panoptic Pappenheims method (Romeis, 1932). Fluorescence of yolk granules and DNP after Pappenheims staining was previously evidenced by Ogorzatek (1975). Electron microscopy
The ovaries were fixed in 2.5% glutaraldehyde in 0.05 m phosphate buffer for a few hours at room temperature. After several rinses in the buffer, the ovaries were postfixed in a mixture of 2% osmium tetroxide and 0.8% potasium ferrocyanide (after McDonald, 1984). After dehydration in a graded acetone series, blocks of tissue were embedded in Epon 812. Ultrathin sections were stained with uranyl acetate and lead
* Department of General Zoology, Zoological Institute, University of Wroclaw, S&335 Wroclaw, ul. Sienkiewicza 21, Poland. t Institute of Zoology, Jagiellonian University, ul. Karasia 6, 304% Krakow, Poland. Received
2 May 1991. 903
904
EI‘AL.
.I KUBRAKIEWICZ
citrate after Reynolds (1963). Semithin sections were stained with 1% methylene blue. Histological as well as semithin sections were examined with Axiophot (Zeiss) light microscope, while ultrathin sections were documented with Tesla BS 500 and Jeol 1200 EX electron microscopes. Results
The ovaries of Siphonophanes grubei are paired, band-shaped organs extending along the abdomen on both sides of the alimentary canal. Germarium, containing oogonia, nurse cells and early previtellogenic oocytes, is placed on the outer lateral side of the ovary band. Oocytes in their euplasmic growth phase and vitellogenesis fill the rest of the gonad lumen (vitellarium). The oocytes arise within groups of isogenic cells. In each group only one oocyte is formed being connected via intercellular bridges with two chains of many nurse cells. The intercellular bridges are also observed between the nurse cells. The AN appear in the ooplasm only as the first signs of differentiation in the oocytenurse cells complex can be structurally evidenced. In most cases the AN are observed in the peripheral ooplasm although some of them may appear in the vicinity of the centrally placed oocyte nucleus. At the time of euplasmic growth the AN become numerous and markedly enlarge their volume. No signs of AN fusion or division are noticed. Simultaneously, the oocyte nucleus migrates from the central position to the peripheral ooplasm. In previtellogenic and early vitellogenic
oocytes the AN are usually confined to the oocyte cortex (Figs. 1. 2); some of them are observed in the vicinity of peripherally located oocyte nucleus (Fig. 1). The latter is relatively small and as a rule contains clumps of partly condensed chromatin. The AN exhibit typical nuclear structure. Their double membrane envelope is pierced by pore complexes (Figs. 4, 6). Connections between the outer membrane of the AN envelope and the cisternae/visicles of endoplasmic reticulum (ER) are observed (Fig. 5). Moreover, during vitellogenesis. stacks of annulate lamellae (AL) are found adjacent to the AN envelope (Fig. 4). Electron lucent and fuzzy content of AN resembles karyoplasm of oocyte nucleus (Fig. 5). Clumps of fine, granular material and some membranous rudiments are also discerned within AN (Fig. 2). Histochemical tests (fluorescence after Pappenheim staining) show that the clumps contain DNPs (Fig. 3). The AN rest in the periplasm till late vitellogenesis; their fate afterwards remains unclear. Discussion AN formation
Although it was not evidenced directly where and how AN might be formed in the ooplasm of S. grubei, arguments exist for their origin from the oocyte nucleus. First, the AN show typical nuclear structure, with nuclear envelope and pore complexes; second, they contain aggregations of fine, granular material, which was shown to consist of DNP; and third, at least at some developmental stages, the AN can be observed in the vicinity of the
Fig. 1. Light micrograph illustrating early vitellogenic oocyte with accompanying Oocyte nucleus (N); accessory nuclei-arrows. X 1600. Fig. 2. Tangential section of the peripheral ooplasm. Numerous accessory seen. Arrows indicate aggregations of fine granular material. ~22.000.
nurse cells.
nuclei (AN) are
Fig. 3. Fluorescence micrograph of early vitellogenic oocytc. Arrows indicate accessory nuclei. Note fluorescence of yolk spheres in the central ooplasm. Pappenheim staining. x600. Fig. 4. Annulate continuity between
lamellae (AL) adjacent to the envelope AL and ER (arrow). ~28,CtCkJ.
of accessory
nucleus
(*). Note
Fig. 5. Small accessory nuclei (‘) in the vicinity of the oocyte nucleus (N). Arrow indicates continuity between accessory nucleus envelope and ER. x24,GQO. Fig. 6. Fully grown accessory
nucleus.
Nuclear
pores are indicated
by arrows.
x29,tkMj.
J. KUBRAKIEWICZ
oocyte nucleus. It was previously postulated for another phyllopod, Artemia salina (Fautrez-Firlefyn, 1951; Anteunis et al., 1966), that the AN were formed as a result of incorporation or engulfment of nurse cells by the adjacent oocyte. Quite recently, these suppositions were verified at the ultrastructural level (Criel. 1989) and eventually rejected. At the time the AN grow in number and volume, the nurse cells show no signs of any sort of degeneration or engulfment; moreover the location of the AN is not restricted to the area of nurse cells adherence. It was convincingly evidenced that the AN in oocytes of insects (King and Fordy, 1970; Meyer et al., 1979; Biliriski and Jankowska, 1987; Bililiski, 1989, 1991) and diplopods (Kubrakiewicz, 1991) originate from the oocyte nucleus envelope. Although the mechanisms might be slightly different among species, the engagement of nuclear envelope in AN formation is undoubted. In the bird louse, Eomenacunthus stramineus. nuclear lamina was found to take part in AN budding (Bilihski, 1989), while in the hymenopteran, Tenthredo olivacea, some cytoskeletal elements, namely microtubules, were found to participate in the process (Biliriski, 1991). The fate of the AN in later stages of oogenesis remains unclear. In oocytes of the pselaphognathan diplopod, Polyxenus lagurus, they arise and presumab!y disintegrate in early previtellogenesis (Kubrakiewicz, 1991); while in insects (Biliriski and Jankowska, 1987) and crustaceans (Criel. 1989) AN persist in the periplasm throughout the whole process of oogenesis. AN function Many functions were ascribed to AN in developing oocytes of different species. Their contribution to egg envelopes formation and vitellogenesis was postulated in hymenopteran insects (Hopkins, 1964; King and Fordy, 1970). The presence of fine, granular RNA-positive aggregations (‘pseudo-nucleoli’) within AN of some insect oocytes suggests that the AN are involved in nucleic acids metabolism. Using histo-
ET AL.
chemical tests (Ag-NOR staining procedure) Bilinski (1989) showed, that the AN from mallophagan oocytes contain rDNA indicating, that they might be involved in rRNA synthesis and transport. Recently, yet another function was attributed to AN of some hymenopteran species. Uneven distribution of AN within ooplasm and their engagement in extrusion of fine granular material (‘nuage’) led to the assumption that the AN in some way participate in establishment of developmental information gradients and morphogenetic signals in hymenopteran oocytes (Bilihski, 1991). We are still uncertain as to the role the AN might play in S. grubei oocytes. At least two possibilities may be disputed here. One of them refers to the DNP character of granular clumps found within the AN, and postulates that like mallophagan oocytes, AN of S. grubei contain some kind of amplified DNA (most probably rDNA) and presumably take part in nucleic acid synthesis and distribution/transport. On the other hand, very rapid development of S. grubei embryo (cellularization of blastoderm is undergone in an oviduct) requires vast amounts of newly formed cytomembranes. The AN and annulate lamellae of S. grubei ooplasm were often found in continuity with cisternae/vesicles of ER, indication the possible function of the AN as cytomembrane ‘generator’ which elaborates membranes directly or with annulate lamellae as an intermediate structures. Engagement of nuclear structures, namely AN or nuclear envelope, in process of cytomembranes formation was supported by Meyer et ul. (1979) and reviewed by Kessel et a/. (1986). Elucidation of functions of AN in oocytes of various invertebrate species obviously needs further investigations, however it has been already shown by recent ultrastructural reports that the roles the AN play can be diverse in different animal groups. Acknowledgement
This work was supported DNS-P-01-050-90-2.
in part by Grant
ACCESSORY NUCLEI IN CRUSTACEAN
OOCYTES
907
Anteunis, A., Fautrez-Firlefyn, N. and Fautrez, J. 1966. L’incorporation de cellules nourricieres par I’oocyte d’Artemiasalina. Etude au microscope electronique. Arch. Biol., 77, 665-676. Bilihski, S. M. 1989. Formation and function of accessory nuclei in the oocytes of the bird louse, Eomenacnnttu straminetu (Insecta, Mallophaga). I. Ultrastructural and histochemical studies. Chromosoma (Berl.), 97,321-326. Bilihski, S. M. 1991. Are accessory nuclei involved in the establishment of developmental gradients in hymenopterans oocytes? Ultrastructural studies. Roux’s Arch. Deo. Biol., 199, 423-426. Bilihski, S. M., Jankowska, W. 1987. Oogenesis in the bird louse, Eomenacantus stramineur (Insecta, Mallophaga). I. General description and structure of the egg capsule. 2001. Jb. Anat., 116, 1-12. Criel, G. R. J. 1989. Morphological study of the ovary of Artemia. In: Cell and Molecular Biology of Artemio Deoelopment (eds. A. H. Warner, Th. MacRae and J. C. Bagshaw), pp. 99-129. Plenum Publishing Corp. Fautrez-Firlefyn, N. 1951. Etude cytochimique des acides nucleiques au tours de la gametogenese et des premieres stades du developpement embryonaire chez Artemia salina. Arch. Biol., 62, 391-438. Goldstein, P. 1981. Accessory nuclei in female Ascaris suum. J. Parositol., 67, 697-701. Hopkins, C. R. 1964. The histochemistry and fine structure of the accessory nuclei in the oocyte of Bombs terrestris. Q. J. Microscop. Sci., 105, 475-480.
Kessel, R. G., Tung, H. N., Beams, H. W. and Lin, J. J.-C. 1986. Is the nuclear envelope a ‘generator’ of membrane? Developmental sequences in cytomembrane elaboration. Cell. Tirs. Rex., 245, 61-68. King, P. E. and Fordy, M. R. 1970. The formation of ‘accessory nuclei’ in the developing oocytes of the parasitoid hymenopterans Ophion luteus (L.) and Apanteles glomeratus (L.). 2. Zellforsch. Mikrosk. Anat., 109, 158-170. Kubrakiewicz, J. 1991. Ovary structure and oogenesis of Polyxenus logurus (L.) (Diplopoda, Pselaphognatha). An ultrastructural study. Zool. Jb. Anat., 121, 81-93. McDonald, K. 1984. Osmium ferrocyanide fixation improves microfilament preservation and membrane visualization in a variety of animal cell types. J. Uhrostruct. Res., 86, 107-188. Meyer, G. F., Sokoloff, S., Wolf, B. E., Brand, B. 1979. Accessory nuclei (nuclear membrane balloons) in the oocytes of the dipteran Phryne. Chromosoma, 75, 89-99. Ogorzatek, A. 1975. Oogenesis in the water bugs. II. The interaction of the germinal vesicle and the follicular epithelium in Naucoris cimicoides L. 2001. Pal., 2512-3, 197-209. Reynolds, E. W. 1963. The use of lead citrate at high pH as an electron-opaque stain electron microscopy. J. Cell Biol., 17, 208212. Romeis, B. 1932. Taschenbuch der mikroskopischen Technik. R. Oldenbourg Verlag. Munchen und Berlin. 382-383. Zissler, D., Sander, K. 1977. The cytoplasmic architecture of the egg cell of Smitria spec. (Diptera, Chironomidae). Rotas Arch. Dee. Biol., 183, 233-248.
J. KUBRAKIEWICZ”,
R. T. ADAMSKI”
and S. M. BlLlkSKlt
ULTRASTRUCTURAL STUDIES ON ACCESSORY NUCLEI IN DEVELOPING OOCYTES OF THE CRUSTACEAN, SIPHONOPHANES GRlJBEl Keywords:
Accessory
nuclei, oogenesis,
Crustacea
ABSTRACT. Numerous accessory nuclei (AN) occur within peripheral cytoplasm of Siphonophmes grubei oocytes. They exhibit typical nuclear structure, with double membrane envelope pierced by pore complexes. Although no explicit evidence was shown, indirect arguments exist indicating that AN originate from the oocyte nucleus. Presence of clumps of DNP material within AN suggests that AN might play some role in amplified DNA metabolism. Participation of AN in cellular membrane elaboration is also postulated.
Introduction
we report ultrastructural and histochemical investigations on AN in another representative of Phyllopoda, Siphonophanes grubei (Dybowski).
Accessory nuclei have been found in oocytes and embryonic cells of various arthropods (Hopkins, 1964; King and Fordy, 1970; Zissler and Sander, 1977; Meyer et al., 1979; Bilihski, 1989, 1991; Kubrakiewicz, 1991) and nematodes (Goldstein, 1981). These peculiar organelles are surrounded by double membrane envelope pierced by nuclear pores and contain electron dense inclusions termed ‘pseudonucleoli’. Additionally, it has been shown, that ‘pseudonucleoli’ are RNA-positive (Meyer et al., 1979). According to King and Fordy (1970), Meyer et al. (1979), Bilifiski (1989, 1991) AN originate from the oocyte nucleus and usually migrate to the peripheral ooplasm, where they persist till late oogenesis. Although the oogenesis of entomostracan crustaceans has been the subject of numerous ultrastructural investigations, the presence of AN has been reported only in the phyllopod, Artemia salina (Criel, 1989). Since the formation and/or function of the AN have not been fully explained, in the present paper
Material and Methods Females of Siphonophanes grubei (Dybowski) were collected from small, astatic water bodies near Wroclaw, Poland. Histological procedure
The ovaries were dissected and fixed in ethanol:acetic acid (3:l). Paraffin sections (6 pm thick) were stained with May-GrunwaldGiemsa according to panoptic Pappenheims method (Romeis, 1932). Fluorescence of yolk granules and DNP after Pappenheims staining was previously evidenced by Ogorzatek (1975). Electron microscopy
The ovaries were fixed in 2.5% glutaraldehyde in 0.05 m phosphate buffer for a few hours at room temperature. After several rinses in the buffer, the ovaries were postfixed in a mixture of 2% osmium tetroxide and 0.8% potasium ferrocyanide (after McDonald, 1984). After dehydration in a graded acetone series, blocks of tissue were embedded in Epon 812. Ultrathin sections were stained with uranyl acetate and lead
* Department of General Zoology, Zoological Institute, University of Wroclaw, S&335 Wroclaw, ul. Sienkiewicza 21, Poland. t Institute of Zoology, Jagiellonian University, ul. Karasia 6, 304% Krakow, Poland. Received
2 May 1991. 903
904
EI‘AL.
.I KUBRAKIEWICZ
citrate after Reynolds (1963). Semithin sections were stained with 1% methylene blue. Histological as well as semithin sections were examined with Axiophot (Zeiss) light microscope, while ultrathin sections were documented with Tesla BS 500 and Jeol 1200 EX electron microscopes. Results
The ovaries of Siphonophanes grubei are paired, band-shaped organs extending along the abdomen on both sides of the alimentary canal. Germarium, containing oogonia, nurse cells and early previtellogenic oocytes, is placed on the outer lateral side of the ovary band. Oocytes in their euplasmic growth phase and vitellogenesis fill the rest of the gonad lumen (vitellarium). The oocytes arise within groups of isogenic cells. In each group only one oocyte is formed being connected via intercellular bridges with two chains of many nurse cells. The intercellular bridges are also observed between the nurse cells. The AN appear in the ooplasm only as the first signs of differentiation in the oocytenurse cells complex can be structurally evidenced. In most cases the AN are observed in the peripheral ooplasm although some of them may appear in the vicinity of the centrally placed oocyte nucleus. At the time of euplasmic growth the AN become numerous and markedly enlarge their volume. No signs of AN fusion or division are noticed. Simultaneously, the oocyte nucleus migrates from the central position to the peripheral ooplasm. In previtellogenic and early vitellogenic
oocytes the AN are usually confined to the oocyte cortex (Figs. 1. 2); some of them are observed in the vicinity of peripherally located oocyte nucleus (Fig. 1). The latter is relatively small and as a rule contains clumps of partly condensed chromatin. The AN exhibit typical nuclear structure. Their double membrane envelope is pierced by pore complexes (Figs. 4, 6). Connections between the outer membrane of the AN envelope and the cisternae/visicles of endoplasmic reticulum (ER) are observed (Fig. 5). Moreover, during vitellogenesis. stacks of annulate lamellae (AL) are found adjacent to the AN envelope (Fig. 4). Electron lucent and fuzzy content of AN resembles karyoplasm of oocyte nucleus (Fig. 5). Clumps of fine, granular material and some membranous rudiments are also discerned within AN (Fig. 2). Histochemical tests (fluorescence after Pappenheim staining) show that the clumps contain DNPs (Fig. 3). The AN rest in the periplasm till late vitellogenesis; their fate afterwards remains unclear. Discussion AN formation
Although it was not evidenced directly where and how AN might be formed in the ooplasm of S. grubei, arguments exist for their origin from the oocyte nucleus. First, the AN show typical nuclear structure, with nuclear envelope and pore complexes; second, they contain aggregations of fine, granular material, which was shown to consist of DNP; and third, at least at some developmental stages, the AN can be observed in the vicinity of the
Fig. 1. Light micrograph illustrating early vitellogenic oocyte with accompanying Oocyte nucleus (N); accessory nuclei-arrows. X 1600. Fig. 2. Tangential section of the peripheral ooplasm. Numerous accessory seen. Arrows indicate aggregations of fine granular material. ~22.000.
nurse cells.
nuclei (AN) are
Fig. 3. Fluorescence micrograph of early vitellogenic oocytc. Arrows indicate accessory nuclei. Note fluorescence of yolk spheres in the central ooplasm. Pappenheim staining. x600. Fig. 4. Annulate continuity between
lamellae (AL) adjacent to the envelope AL and ER (arrow). ~28,CtCkJ.
of accessory
nucleus
(*). Note
Fig. 5. Small accessory nuclei (‘) in the vicinity of the oocyte nucleus (N). Arrow indicates continuity between accessory nucleus envelope and ER. x24,GQO. Fig. 6. Fully grown accessory
nucleus.
Nuclear
pores are indicated
by arrows.
x29,tkMj.
J. KUBRAKIEWICZ
oocyte nucleus. It was previously postulated for another phyllopod, Artemia salina (Fautrez-Firlefyn, 1951; Anteunis et al., 1966), that the AN were formed as a result of incorporation or engulfment of nurse cells by the adjacent oocyte. Quite recently, these suppositions were verified at the ultrastructural level (Criel. 1989) and eventually rejected. At the time the AN grow in number and volume, the nurse cells show no signs of any sort of degeneration or engulfment; moreover the location of the AN is not restricted to the area of nurse cells adherence. It was convincingly evidenced that the AN in oocytes of insects (King and Fordy, 1970; Meyer et al., 1979; Biliriski and Jankowska, 1987; Bililiski, 1989, 1991) and diplopods (Kubrakiewicz, 1991) originate from the oocyte nucleus envelope. Although the mechanisms might be slightly different among species, the engagement of nuclear envelope in AN formation is undoubted. In the bird louse, Eomenacunthus stramineus. nuclear lamina was found to take part in AN budding (Bilihski, 1989), while in the hymenopteran, Tenthredo olivacea, some cytoskeletal elements, namely microtubules, were found to participate in the process (Biliriski, 1991). The fate of the AN in later stages of oogenesis remains unclear. In oocytes of the pselaphognathan diplopod, Polyxenus lagurus, they arise and presumab!y disintegrate in early previtellogenesis (Kubrakiewicz, 1991); while in insects (Biliriski and Jankowska, 1987) and crustaceans (Criel. 1989) AN persist in the periplasm throughout the whole process of oogenesis. AN function Many functions were ascribed to AN in developing oocytes of different species. Their contribution to egg envelopes formation and vitellogenesis was postulated in hymenopteran insects (Hopkins, 1964; King and Fordy, 1970). The presence of fine, granular RNA-positive aggregations (‘pseudo-nucleoli’) within AN of some insect oocytes suggests that the AN are involved in nucleic acids metabolism. Using histo-
ET AL.
chemical tests (Ag-NOR staining procedure) Bilinski (1989) showed, that the AN from mallophagan oocytes contain rDNA indicating, that they might be involved in rRNA synthesis and transport. Recently, yet another function was attributed to AN of some hymenopteran species. Uneven distribution of AN within ooplasm and their engagement in extrusion of fine granular material (‘nuage’) led to the assumption that the AN in some way participate in establishment of developmental information gradients and morphogenetic signals in hymenopteran oocytes (Bilihski, 1991). We are still uncertain as to the role the AN might play in S. grubei oocytes. At least two possibilities may be disputed here. One of them refers to the DNP character of granular clumps found within the AN, and postulates that like mallophagan oocytes, AN of S. grubei contain some kind of amplified DNA (most probably rDNA) and presumably take part in nucleic acid synthesis and distribution/transport. On the other hand, very rapid development of S. grubei embryo (cellularization of blastoderm is undergone in an oviduct) requires vast amounts of newly formed cytomembranes. The AN and annulate lamellae of S. grubei ooplasm were often found in continuity with cisternae/vesicles of ER, indication the possible function of the AN as cytomembrane ‘generator’ which elaborates membranes directly or with annulate lamellae as an intermediate structures. Engagement of nuclear structures, namely AN or nuclear envelope, in process of cytomembranes formation was supported by Meyer et ul. (1979) and reviewed by Kessel et a/. (1986). Elucidation of functions of AN in oocytes of various invertebrate species obviously needs further investigations, however it has been already shown by recent ultrastructural reports that the roles the AN play can be diverse in different animal groups. Acknowledgement
This work was supported DNS-P-01-050-90-2.
in part by Grant
ACCESSORY NUCLEI IN CRUSTACEAN
OOCYTES
907
Anteunis, A., Fautrez-Firlefyn, N. and Fautrez, J. 1966. L’incorporation de cellules nourricieres par I’oocyte d’Artemiasalina. Etude au microscope electronique. Arch. Biol., 77, 665-676. Bilihski, S. M. 1989. Formation and function of accessory nuclei in the oocytes of the bird louse, Eomenacnnttu straminetu (Insecta, Mallophaga). I. Ultrastructural and histochemical studies. Chromosoma (Berl.), 97,321-326. Bilihski, S. M. 1991. Are accessory nuclei involved in the establishment of developmental gradients in hymenopterans oocytes? Ultrastructural studies. Roux’s Arch. Deo. Biol., 199, 423-426. Bilihski, S. M., Jankowska, W. 1987. Oogenesis in the bird louse, Eomenacantus stramineur (Insecta, Mallophaga). I. General description and structure of the egg capsule. 2001. Jb. Anat., 116, 1-12. Criel, G. R. J. 1989. Morphological study of the ovary of Artemia. In: Cell and Molecular Biology of Artemio Deoelopment (eds. A. H. Warner, Th. MacRae and J. C. Bagshaw), pp. 99-129. Plenum Publishing Corp. Fautrez-Firlefyn, N. 1951. Etude cytochimique des acides nucleiques au tours de la gametogenese et des premieres stades du developpement embryonaire chez Artemia salina. Arch. Biol., 62, 391-438. Goldstein, P. 1981. Accessory nuclei in female Ascaris suum. J. Parositol., 67, 697-701. Hopkins, C. R. 1964. The histochemistry and fine structure of the accessory nuclei in the oocyte of Bombs terrestris. Q. J. Microscop. Sci., 105, 475-480.
Kessel, R. G., Tung, H. N., Beams, H. W. and Lin, J. J.-C. 1986. Is the nuclear envelope a ‘generator’ of membrane? Developmental sequences in cytomembrane elaboration. Cell. Tirs. Rex., 245, 61-68. King, P. E. and Fordy, M. R. 1970. The formation of ‘accessory nuclei’ in the developing oocytes of the parasitoid hymenopterans Ophion luteus (L.) and Apanteles glomeratus (L.). 2. Zellforsch. Mikrosk. Anat., 109, 158-170. Kubrakiewicz, J. 1991. Ovary structure and oogenesis of Polyxenus logurus (L.) (Diplopoda, Pselaphognatha). An ultrastructural study. Zool. Jb. Anat., 121, 81-93. McDonald, K. 1984. Osmium ferrocyanide fixation improves microfilament preservation and membrane visualization in a variety of animal cell types. J. Uhrostruct. Res., 86, 107-188. Meyer, G. F., Sokoloff, S., Wolf, B. E., Brand, B. 1979. Accessory nuclei (nuclear membrane balloons) in the oocytes of the dipteran Phryne. Chromosoma, 75, 89-99. Ogorzatek, A. 1975. Oogenesis in the water bugs. II. The interaction of the germinal vesicle and the follicular epithelium in Naucoris cimicoides L. 2001. Pal., 2512-3, 197-209. Reynolds, E. W. 1963. The use of lead citrate at high pH as an electron-opaque stain electron microscopy. J. Cell Biol., 17, 208212. Romeis, B. 1932. Taschenbuch der mikroskopischen Technik. R. Oldenbourg Verlag. Munchen und Berlin. 382-383. Zissler, D., Sander, K. 1977. The cytoplasmic architecture of the egg cell of Smitria spec. (Diptera, Chironomidae). Rotas Arch. Dee. Biol., 183, 233-248.