Recent Advances in Insect Embryology in I apan and Poland
Edited by H. Ando and Cz. Iura
Arthropod. EmbryoL. SQC. Ipn.
(ISEBU Co. Ltd., Tsukuba) 198731

Ultrastructure of Oogonia
in Germarium of Adult Femalesof Allacma Jusca (Collembola)

Elzbieta KISIEL
Synopsis
Cystocytes in germarium of Allacma fusca are distributed in branching clusters. The cystocytes are morphologically identical and interconnected with cytoplasmic bridges. The ultrastructural data on cystocytes, during their interphase, with special reference to cytoplasmic
bridges are presented.

IntroductionAllacma fusca (Collembola, Apterygota) inhabits forests of Europe, North Africa
and North America. These insects can be found on tree trunks on roting wooden logs,on stones and occasionally on mushrooms.
The reports on ultrastructure of cystocytes within ovaries of Apterygota are quite
scarce (Matsuzaki, 1973; Palevody, 1976; Bitsch, 1980; Bili6ski, 1983). Cystocytes develope in synchronic mitotic divisions, from cystoblasts. Their number (N) is species
dependent. However, in most cases this is equal to: N = 2n, where n = numbers following mitotic divisions.
The known facts about A. fusca are that sack like ovaries are of polytrophic type.
The germ aria placed on top of ovarioles are folded towards lower part of the abdomen(Krzysztofowicz, 1977). The present work is devoted to ultrastructural investigation ofcystocytes in germarium of adult females.

Material and Methods
Females of Allacma fusca were collected near Krak6w (South of Poland) during

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E. KisielFig. 1. Photomicrograph of the gonad fragment. G, germarium; T, trophocytes. X 540
Fig. 2. Electron micrograph of the fragment of germarium. G, Golgi apparatus; M, mitochondria; N, nucleus. X 12.000.

Germarium of Allacma fusca

33

early June. They were decapitated and preliminary fixed in 2.5 % glutaraldehyde in
0.1 M phosphate buffer, pH 7.4. In all the osmotic pressure was 410 mosmol. After
1.5 hr the fixed specimens were put into 1 % tannic acid, in 0.1 M phosphate buffer,
pH 7.4 with addition of sucrose (5.8 g in 100 ml of solution) for 24 hr. After this, thematerial was rinsed several times in the phosphate buffer, then in 1 % sodium sulfateand postfixed in 2 % OS04 in O. 1 M phosphate buffer with addition of sucrose (2.56 gof sucrose in 100 ml of the solution).
Following that the material was dried in graded series of alcohol and acetone andembedded in Epon 812. Ultrathin sections were treated with uranyl acetate and leadcitrate and examined in Tesla BS 500 electron microscope. Semithin sections werestained with 1 % solution of methylene blue in borax.

Results
Oogenesis in ovaries of A. fusca is a synchronic process. In germarium the germ
cells undergo mitotic divisions resulting in the clusters of cystocytes (Fig. 1). In eachcystocyte cluster about 16 morphologically identical cells occur. They are interconnected with cytoplasmic bridges (Fig. 3). The cystocytes in interphase have very large
nucleus and little of cytoplasm (Fig. 2). In the nucleus distinct heterochromatine
aggregations and in the cytoplasm ribosomes, polyribosomes, a few mitochondria anddictyosomes can be seen (Figs. 2, 3). Finally, one should mention centrioles which canalso be seen in the cytoplasm. The centrioles are often surrounded by a "halo" of
mitochondria (Fig. 3 a). Cytoplasmic bridges are built up like those described inanother Apterygota. The bridge rims are slightly dilated and lined up with afilamentous electron-dense material. In the bridge an irregular network composed of
medium density material occurs (Fig. 3). This is particularly evident on sections parallel to plane of the bridge. However, the network examined on sections with different
spatial orientation appears as loosely distributed collection of plate-like structures with
no apparent interconnections.
Through the empty spaces of the network there pass microtubules, being probably
the remnants of the mitotic spindle. Very often, the bridges are distributed in a particular arrangement - one perpendicular to another (see Discussion).

Discussion
Like in the case of another apterygotan insects, with the ovaries of polytrophictype, also in A. fusca the observed cystocyte clusters were interconnected with cytoplasmic bridges. The cytoplasmic bridges belonging to a single cystocyte can be mutuallyperpendicular one to another. Such the arrangement is typical for branching cystocyte
clusters of Pterygota (King and Biining, 1985). Thus it seems that the cystocyte clusters in A. fusca can be a branched-like structures; the first such a case reported forApterygota. Up to now only linear clusters of cystocytes were known in apterygotan insects (Matsuzaki, 1973; Palevody, 1976; Bilinski, 1983).
It must be stressed out, however, that during the present investigation the prob-34

Fig. 3.

E. Kisiel

Electron micrograph of the fragment of germarium. Cytoplasmic bridges can be seen(arrows). G, germarium; M, mitochondria; m, microtubules; N, nucleus . X 22 ,000.
Fig. 3a. Centriole surrounded with mitochondria. X 37,200.

Germarium of Allacma fusca

35

lem: whether the cystocyte clusters in A. fusca are built up, and develop according tothe scheme as in Pterygota (King et al., 1983), or if the branchings in the clusters develop in random, remains unsolved.
The final number of cystocytes is close, but not necessarily strictly equal to 16 (i.
e., 24). Similar breaking of the rule N = 2" is known for Campodeidae (Lepidocampa,Asaba and Ando, 1978; Campodea, Bilinski, 1983).
Ultrastructure of cystocytes in A. fusca during interphase in similar like that forother Apterygota (Palevody, 1976; Bilinski, 1983). In particular the cytoplasmic
bridges described in Isotomurus palustris (Palevody, 1976) do not differ from these examined in A. fusca.
The centrioles in the cystocytes can be attributed to mitotic activity of the cells.

References
Asaba, H. and H. Ando, 1978. Ovarian structures and oogenesis in Lepidocampa weberi Oudemans(Diplura: Campodeidae). Int.]. Insect Morphol. Embryol. 7: 405-414.
Bilinski, S., 1983. Differentiation of the oocyte and nurse cells in an apterygote insect (Campodea).
Tiss. Cell 15: 965-973.
Bitsch, J., 1980. Ultrastructure des ovocytes et vitellogenese chez Lepismachilis targionii (Grassi)(Thysanura: Machilidae). Int.]' Insect Morpho!. Embryo!. 9: 297-313.
King, R. C. and J. Buning, 1985. The origin and functioning of insect oocytes and nurse cells. In
G. A. Kerkut and L. J. Gilbert (eds. ), Comprehensive Insect Physiology, Biochemistry andPharmacology, Vol. I, Embryogenesis and Reproduction, 38-82. Pergamon Press, Oxford,New York.
- - - - - , J. D. Cassidy and A. Rousset, 1982. The formation of clones of interconnected
cells during gametogenesis in insects. In R. C. King and H. Akai (eds. ), Insect Ultrastructure, Vol. I, 3-31. Plenum, New York.
Krzysztofowicz, A., 1977. Les etudes comparatives sur la morphologie des ovaries chez les Collemboles. Rev. Ecol. Bioi. Sol 14: 81-90.
Matsuzaki, M., 1973. Oogenesis in the springtail, Tomocerus minutus Tulberg (Collembola:Tomoceridae). Int.]. Insect Morphol. Embryol. 2: 335-349.
Palevody, C., 1976. L'Ovogenese chez les Collemboles Isotomides Cytologie et Approche Physiologique. Doctoral thesis, Universite Paul Sabatier de Toulouse.

Author's address: MSc. E. Kisiel

Department of Systematic Zoology,
Institute of Zoology, Jagiellonian
University, ul. Karasia 6, 30-060
Krak6w, Poland