Embryonic development of the hemipteran insect Rhodnius prolixus

The embryonic development of the hemipteran insect Rhodnius prolixus was studied by use of contemporary light and electron microscopy. Embryos were staged according to days postoviposition. Eggs laid on day one complete blastoderm formation and anatrepsis, the first phase of blastokinesis, by day 5. The embryo develops in a cephalocaudal orientation which is 180° to the anteroposterior axis of the egg. Subsequent development, prior to the second phase of blastokinesis (katatrepsis), leads to segmentation of the germ band, evagination of appendages, and histogenesis of germ layers. Concomitantly with these events, the amnion undergoes dramatic change. By day 7 the embryo begins a 180° revolution while migrating to the ventral surface of the yolk. This restores its polarity with respect to that of the egg and facilitates hatching. The serosa contracts, pulling the amnion and embryo anteriorly. Eventually the serosa is internalized at a point dorsal to the head and the lateral walls of the embryo grow up and surround the yolk. Development continues until day 15 when the embryo hatches as a first instar larva.     

Embryonic development of the jumping bristletail Pedetonutus unimaculatus Machida,with special reference to embryonic membranes (Hexapoda: Microcoryphia,Machilidae)

In the machilid Pedetonutus unimaculatus, a germ disc is formed by the aggregation and proliferation of cells within a broadly defined embryonic area. Cells adjacent to the embryonic area form the serosal fold that grows beneath the embryo. Then the embryonic margin is extended to form a cell layer or amnion that lies between the embryo and serosal fold. Thus, an amnioserosal fold is formed by the addition of the amnion to the serosal fold. Serosal cells cover the entire surface of the egg and begin to secrete a serosal cuticle. Soon the amnioserosal fold is withdrawn, and the embryo is exposed to the egg surface. The spreading amnion replaces the serosal cells that finally degenerate through the formation of a secondary dorsal organ. In the areas of amnion anterior and lateral to the embryo, yolk folds form and encompass the embryo. The amnion is a provisional dorsal closure and never participates in the formation of the definitive one. The amnioserosal fold of the Microcoryphia appears to have the functional role of secreting a serosal cuticle beneath the embryo. This fold of the Microcoryphia may be regarded as an ancestral form of the amnioserosal folds of the Thysanura-Pterygota. the yolk folds may appear to be passive transformation of the yolk mass linked to positioning of the growing embryo within the egg. There is no evidence that the yolk folds and the cavity appearing between them in the Microcoryphia are homologous to the amnioserosal fold and amniotic cavity in the Thysanura-Pterygota. The yolk folds appear to be one of the embryological autapomorphies in the Microcoryphia. © 1994 Wiley-Liss, Inc.     

Embryogenesis of the glowworm Rhagophthalmus ohbai Wittmer (Insecta: Coleoptera, Rhagophthalmidae), with emphasis on the germ rudiment formation

The early embryonic development and features of the developing embryo of the glowworm Rhagophthalmus ohbai are described chiefly by light microscopy, with emphasis on the germ rudiment formation and its phylogenetic implication. The egg period is 30-34 days at about 23 degrees C. The newly laid egg is a short ellipsoid, 1.09 by 0.78 mm in size, and the size increases to 1.15 by 0.95 mm by 17 days after oviposition. Cleavage is of the typical superficial type. The germ disk is formed by cell aggregation of the embryonic area at the anterior end of the egg. The central part of the germ disk then sinks into the yolk and the spherical germ rudiment is formed by fusion of the amnioserosal folds extended from all margins of the germ disk. The inner region of the germ rudiment soon becomes slender and develops into the short embryo, whereas the outer region facing the anterior end is extended to form the thin amnion. The embryo then rapidly elongates, the elongation being accompanied by embryo segmentation and formation of appendages. The submerged condition of the embryo persists until about 17 days after oviposition (about 1 day before embryonic revolution) and thereafter the embryo becomes superficial in position. The presence of the following embryonic characters in R. ohbai supports the molecular data placing it within the Lampyridae: 1) formation of a spherical germ rudiment near the anterior end of the egg, and 2) the submerged condition of the developing embryo persists until shortly before revolution.     

Distinct functions of the Tribolium zerknüllt genes in serosa specification and dorsal closure

BACKGROUND: In the long-germ insect Drosophila, a single extraembryonic membrane, the amnioserosa, covers the embryo at the dorsal side. In ancestral short-germ insects, an inner membrane, the amnion, covers the embryo ventrally, and an outer membrane, the serosa, completely surrounds the embryo. An early differentiation step partitions the uniform blastoderm into the anterior-dorsal serosa and the posterior-ventral germ rudiment giving rise to amnion and embryo proper. In Drosophila, amnioserosa formation depends on the dorsoventral patterning gene zerknüllt (zen), a derived Hox3 gene. RESULTS: The short-germ beetle Tribolium castaneum possesses two zen homologs, Tc-zen1 and Tc-zen2. Tc-zen1 acts early and specifies the serosa. The loss of the serosa after Tc-zen1 RNAi is compensated by an expansion of the entire germ rudiment toward the anterior. Instead of the serosa, the amnion covers the embryo at the dorsal side, and later size regulation normalizes the early fate shifts, revealing a high degree of plasticity of short-germ development. Tc-zen2 acts later and initiates the amnion and serosa fusion required for dorsal closure. After Tc-zen2 RNAi, the amnion and serosa stay apart, and the embryo closes ventrally, assuming a completely everted (inside-out) topology. CONCLUSIONS: In Tribolium, the duplication of the zen genes was accompanied by subfunctionalization. One of the paralogues, Tc-zen1, acts as an early anterior-posterior patterning gene by specifying the serosa. In absence of the serosa, Tribolium embryogenesis acquires features of long-germ development with a single extraembryonic membrane. We discuss implications for the evolution of insect development including the origin of the zen-derived anterior determinant bicoid.     

Embryogenesis of the dipluran Lepidocampa weberi Oudemans (hexapoda: diplura, campodeidae): formation of dorsal organ and related phenomena

The developmental changes of embryonic membranes of a dipluran Lepidocampa weberi, with special reference to dorsal organ formation, are described in detail by light, scanning, and transmission electron microscopies. Newly differentiated germ band and serosa secrete the blastodermic cuticle at the entire egg surface beneath the chorion. Soon after, the serosal cells start to move dorsad. All the serosal cells finally concentrate at the dorsal side of the egg and form the dorsal organ. During their concentration, the serosal cells attenuate their cytoplasm to form filaments. The extensive area from which the serosa has receded is occupied by a second embryonic membrane, the amnion, which originates from the embryonic margin. The embryo and newly emerged amnion then secrete three fine cuticular layers, "cuticular lamellae I, II, and III," above which the filaments of the (developing) dorsal organ are situated. With the progression of definitive dorsal closure, the amnion reduces its extension, the dorsal organ is incorporated into the body cavity of the embryo, and the amnion and dorsal organ finally degenerate.The dorsal organ of diplurans is formed by the concentration of whole serosal cells, while that of collembolans is formed by the direct differentiation of a part of serosal cells. However, the dorsal organs of diplurans and collembolans closely resemble each other in major aspects, including that of ultrastructural features, and there is no doubt regarding their homology. The amnion, which has been regarded as being a characteristic of Ectognatha, also develops in the Diplura. This might suggest a closer affinity between the Diplura and Ectognatha than previously believed.     

The amnioserosa is an apomorphic character of cyclorrhaphan flies

In developing insect eggs the cells of the blastoderm adopt either an embryonic or an extraembryonic fate. The extraembryonic tissue consists of epithelia, termed amnion and serosa, which wrap the germ band embryo. The serosa develops directly from part of the blastoderm and surrounds the embryo as well as the yolk. The amnion develops from the margins of the germ band and in most insect species generates a transient ventral cavity for the developing embryo. The amniotic cavity and the serosa have been reduced in the course of dipteran evolution. The insect order of Diptera includes the paraphyletic Nematocera, including gnats and mosquitoes, and the more derived monophyletic Brachycera, the true flies. Nematocera develop within an amniotic cavity and the surrounding serosa, whereas cyclorrhaphan Brachycera do not. This observation implies that the amnion and serosa have been reduced before the radiation of the monophyletic cyclorrhaphan flies. Here I show that an amniotic cavity is formed during embryogenesis of the horsefly Haematopota pluvialis (Tabanidae) and the dancefly Empis livida (Empididae). The results suggest that extraembryonic tissue was reduced in the stem lineage of cyclorrhaphan flies, with consequences for the molecular basis of pattern formation along the anterior-posterior axis of the embryo. Received: 21 October 1999 / Accepted: 17 January 2000     

External features of the developing embryo of the stonefly,Kamimuria tibialis (pictet) (plecoptera,perlidae)

External features of the egg, developing embryo, and first instar nymph of Kamimuria tibialis are described. The embryonic development from the germ disc to the full-grown embryo is divided into 12 stages. The saclike embryonic rudiment is formed by the bending and folding of the germ disc. The embryo first elongates at the egg surface and then sinks into the yolk due to caudal flexure. In the head, four paired protocerebral lobes differentiate and the fourth lobes are thought to be the rudiments of preantennal ganglia. The columnar serosal cells appear at the posterior pole of the egg and they disappear before katatrepsis. The coniform chloride cells occur at the hind margins of the first nine abdominal segments in the full-grown embryo and first instar nymph. Amnion formation in K. tibialis is very similar to that of Allonarcys proteus and the Isoptera. It is proposed that the immersed type of growth pattern of embryos is divided into two subtypes in hemimetabolous insects; one is in the Palaeoptera and Paraneoptera, and the other is in the Plecoptera, Orthoptera, Notoptera, Isoptera, Embioptera, and the blattarian, Periplaneta americana.     

Female genital configuration in the classification of Lepidoptera

In Coleoptera, Neuroptera, and Megaloptera, and the panorpoid orders Diptera, Trichoptera, and Mecoptera the common oviduct is ventral to, or opens into, the vagina or genital chamber. In Lepidoptera, in the superfamilies Micropterigoidea, Eriocranioidea, Incurvarioidea, and Nepticuloidea, the common oviduct enters the copulatory chamber ventrally; in Mnesarchaeidae, Hepialoidea, and all Ditrysia auct. the common oviduct is dorsal to the copulatory chamber, and the vagina (that region posterior to the entry of the spermatheca) opens separately from the genital ostium. Lepidoptera are unique in the complex and various arrangements of the ectodermal elements in the female genitalia.

The arrangements of, and connections between rectal and genital structures in representatives of Megaloptera, Neuroptera, and the panorpoid orders are re‐examined for comparison with the systems found in Zeugloptera, Dacnonypha, Monotrysia, and Ditrysia auct.

The Zeugloptera are here included in Lepidoptera because they have a circumcloacal chamber. Other female zeuglopteran genital structures intergrade with those of Dacnonypha, here restricted to Eriocraniidae, Agathiphagidae, Lophocoronidae, and the divergent Acanthopteroctetes. Dacnonypha have a less specialised spermathecal and vaginal structure than do most of the Monotrysia, here restricted to Incurvarioidea and Nepticuloidea (including Tischeriidae); many Monotrysia lack a cloaca, whereas it is always present in Dacnonypha.

There is no basis for retaining either Mnesarchaeidae or Hepialoidea in Monotrysia auct., as the dorsal common oviduct and the two genital openings indicate that these groups are ditrysian. They are here regarded as exoporian Ditrysia, a group characterised by the lack of a free, tubular ductus seminalis. A fixed gutter or channel between ostium and ovipore characterises the Hepialoidea, and the absence of this channel (ostium and ovipore opposable within an external genital pouch) characterises Mnesarchaeidae.

The endoporian Ditrysia all have a free, tubular ductus seminalis; where a cloaca is present it is incomplete, i.e., combines ovipore and rectum but never copulatory structures, in contrast to the complete cloaca found in Zeugloptera, Dacnonypha, and many Monotrysia. The endoporian Ditrysia comprise all other superfamilies, i.e., about 97% of species of Lepidoptera.     

Tribolium embryogenesis: a SEM study of cell shapes and movements from blastoderm to serosal closure

Embryogenesis in the beetle Tribolium is of increasing interest to both molecular and evolutionary biology because it differs from the Drosophila paradigm by its type of segment specification (short- vs. long-germ) and by the extensive epithelial envelopes – amnion and serosa – that are typical of most insects but not of higher dipterans. Using scanning electron microscopy of DAPI staged embryos we document development in Tribolium castaneum from blastoderm to completion of the envelopes, recording many details not otherwise accessible; we also provide a time table of the respective stages at 30°C. The nascent blastoderm cells remain basally confluent with the yolksac until after the 13th (=last synchronous) mitotic cycle. The cells in the prospective serosa – the first domain to segregate visibly from the uniform blastoderm – carry surface protrusions likely to contact the overlying vitelline envelope. The embryonic rudiment, the other (and larger) blastodermal domain, gives rise to amnion and germ anlage. In the latter, visible differentiation begins with a ”primitive pit” reminiscent of the posterior midgut rudiment of Drosophila. The subsequent invagination of the mesoderm resembles Drosophila gastrulation, except in the head region where the median groove extends through the entire preoral region. The prospective amnion starts differing visibly from the germ anlage during early gastrulation. It then folds underneath the spreading serosa and, advancing with the latter, closes the amniotic cavity at the ventral face of the germband. The largest (=posterior) amniotic fold covers a crestlike protrusion of the yolksac. Together with marked changes in the shape and arrangement of the amnion cells, this protrusion may contribute to the fold’s elevation and early progress. Received: 12 August 1999 / Accepted: 4 November 1999     

Embryogenesis of the honeybee apis mellifera l. (hymenoptera : apidae): An sem study

Our SEM study of honeybee, Apis mellifera (Hymenoptera : Apidae), embryogenesis is based on embryos fixed at 1 hr intervals from oviposition to hatching. Embryos of equal age showed little variation, so that staging could be based on developmental age. Our data confirm many earlier light microscopical observations, but are at variance with some others. The cytoplasmic connections between the future blastoderm cells and the central yolk system are severed only at the onset of gastrulation. The serosa derives from cells which immigrate into the dorsal strip and then join up to form a pre-serosa bordering the germ band rims. When the serosa has detached, the amnion grows out from the germ band margins and serves as a provisional dorsal epithelium right from the beginning. Germ band segmentation is followed by the transient regression of every second transverse groove (double segment pattern). The germ band flanks grow dorsally and replace the amnion a few hr before hatching (dorsal closure). The tracheal openings which form half-way between segment borders are closed temporarily by the embryonic cuticle; similar openings above the labial buds contribute to the tentorium rather than the tracheal system. Most head appendages retain bud character until long after hatching. The events observed in the SEM are linked in a diagram to the stage series based on living embryos.     

Evolution of the dorsal-ventral patterning network in the mosquito, Anopheles gambiae

The dorsal-ventral patterning of the Drosophila embryo is controlled by a well-defined gene regulation network. We wish to understand how changes in this network produce evolutionary diversity in insect gastrulation. The present study focuses on the dorsal ectoderm in two highly divergent dipterans, the fruitfly Drosophila melanogaster and the mosquito Anopheles gambiae. In D. melanogaster, the dorsal midline of the dorsal ectoderm forms a single extra-embryonic membrane, the amnioserosa. In A. gambiae, an expanded domain forms two distinct extra-embryonic tissues, the amnion and serosa. The analysis of approximately 20 different dorsal-ventral patterning genes suggests that the initial specification of the mesoderm and ventral neurogenic ectoderm is highly conserved in flies and mosquitoes. By contrast, there are numerous differences in the expression profiles of genes active in the dorsal ectoderm. Most notably, the subdivision of the extra-embryonic domain into separate amnion and serosa lineages in A. gambiae correlates with novel patterns of gene expression for several segmentation repressors. Moreover, the expanded amnion and serosa anlage correlates with a broader domain of Dpp signaling as compared with the D. melanogaster embryo. Evidence is presented that this expanded signaling is due to altered expression of the sog gene.     

Embryonic development of a collembolan,Tomocerus cuspidatus Börner, 1909: With special reference to the development and developmental potential of serosa (Hexapoda: Collembola,Tomoceridae)

The embryogenesis of a collembolan, Tomocerus cuspidatus, was examined and described, with special reference to the development of serosa and its developmental potential. As a result of cleavage, which starts with holoblastic cleavage and changes to the superficial type, the blastoderm forms. At the center of the dorsal side of the egg, the primary dorsal organ develops. The mesoderm is segregated beneath the entire blastoderm, excluding the primary dorsal organ. The mesoderm then migrates to the presumptive embryonic area, and the embryonic and extra-embryonic areas differentiate. The area lined with mesoderm is the embryo, and that devoid of it is the serosa. Owing to blastokinesis completion, the extra-embryonic area or the serosa is highly stretched, and the serosal cells are often found to undergo mitosis. The serosa possesses the ability to differentiate into the body wall. It was confirmed, in contrast to the previous understanding, that the serosal cells do not degenerate, but participate in the formation of the body wall or definitive dorsal closure. Integrating this newly obtained information and other embryological evidence, the basal splitting of Hexapoda was phylogenetically discussed and reconstructed, and a phylogeny formulated as “Ellipura (= Protura + Collembola) + Cercophora (= Diplura and Ectognatha)” was proposed.     

Phylogenetic relationships among the lepidopteran and trichopteran suborders (Insecta) from the embryological standpoint1

Adopting the cladistic method in comparative embryology, 27 embryonic characters were analyzed to reconstruct the phylogenetic relationships among the lepidopteran and trichopteran suborders, viz., Annulipalpia, Integripalpia, Zeugloptera, Dacnonypha, Exoporia, Monotrysia, and Ditrysia. The resultant cladogram is basically coincident with that proposed by Kristensen . The order Trichoptera and Lepidoptera constitute a monophyletic group on the basis of one synapomorphy, the presence of well developed silk glands in embryos. The Trichoptera are separable from the Lepidoptera by the states of four characters. The Trichoptera, as a whole, are quite homogenous, and embryological data provide no rational ground for the separation of this order into the Annulipalpia and Integripalpia at a subordinal level. On the contrary, the embryonic development of the Lepidoptera becomes divergent from the most primitive condition to a specialized one according to suborders. The Zeugloptera are the sister group of all other Lepidoptera, because they share two apomorphies with the latter. The Dacnonypha are the most primitive next to the Zeugloptera, and have a sister-group relationship with the Exoporia + (Monotrysia + Ditrysia), being held together with the latter by five synapomorphies. Although the Exoporia retain almost as many plesiomorphic characters as the Dacnonypha, they have a sister-group relationship with the Monotrysia + Ditrysia, as inferred on the basis of two synapomorphies. The Monotrysia and Ditrysia have a sistergroup relationship, and are the most advanced groups in the Lepidoptera judging from their shared acquisition of many apomorphic characters.     

Ultrastructure of embryonic envelopes and integument ofOncopeltus fasciatus dallas (Insecta,Heteroptera)

Summary The embryo ofOncopeltus fasciatus forms a typical secondary dorsal organ (SDO). It develops after katatrepsis from the contracting serosa, the cells of which decrease in diameter but increase considerably in height. After 66 h, the SDO represents a protrusion of the serosal epithelium above the head and is then reduced to a disc-shaped formation, which sinks into the yolk, where it disintegrates after 80 h.During its typical expression, between 66 and 78 h, the SDO shows a zonal arrangement of its cell organelles. The nucleus, which is located in the basal cell region, has a very irregular outline and includes several nucleoli and globular inclusion bodies. Rough and smooth ER are well developed around the nucleus and suggest the involvement of the organ in protein secretion as well as in lipid metabolism. Electron-lucent vacuoles and electron-dense granules, sometimes enclosed in the vacuoles, accumulate in the apical cell region, and are obviously extruded into the peripheral (extraembryonic) space. The formation of intercellular clefts and delicate cytoplasmic extensions facing the yolk and microvilli facing the periphery evidence a transporting function of the epithelium. Blisters intercalated in extended junctional complexes between apical cell regions point to the transport of solutes.Because of the similarities of the processes observed in the SDO and in Malpighian tubules of larvae, an excretory function of the SDO is suggested. Final products of yolk and embryo are apparently transported to the extraembryonic space, where they accumulate during embryogenesis.Phylogeny, relationship, and function of the different embryonic glands in Arthropoda (primary and secondary DO and pleuropodia) are discussed.Dedicated to Prof. Dr. B. Scharrer on the occasion of her birthdaySupported by the Deutsche ForschungsgemeinschaftI am grateful to Miss K. Schmidtke and Mrs. M. Ullmann for technical assistance     

Alimentary canal formation in the stonefly,Kamimuria tibialis (pictet) (Plecoptera : Perlidae)

The alimentary canal formation in the stonefly, Kamimuria tibialis (Plecoptera : Perlidae) is described. The stomodaeum is formed as in other insect embryos. The proctodaeum is derived from the ectodermal fold an the caudal end of the embryo without the contribution of the amnion. The 3 Malpighian tubules develop from the blind end of the proctodaeum. The rectal pad is formed by the thickening of the dorsal wall of the proctodaeum. The midgut epithelium rudiment arises only from the blind end of the proctodaeum, i.e. it is completed by unipolar formation instead of bipolar. The yolk cells do not contribute to the formation of the midgut epithelium. The alimentary canal is transformed during the 1st nymphal instar and becomes functional in the next instar. The stomodaeum is differentiated into 3 parts: pharynx, oesophagus, and proventriculus. The midgut becomes shortened and its epithelium is well developed. Gastric caeca with tapering processes are formed.     

The embryonic development of the rhabdocoel flatworm Mesostoma lingua (Abildgaard, 1789)

The embryonic development of the flatworm Mesostoma lingua was studied using a combination of life observation and histological analysis of wholemount preparations and sections (viewed by both light and electron microscopy.) We introduce a series of stages defined by easily recognizable morphological criteria. These stages are also applicable to other platyhelminth taxa that are currently under investigation in our laboratory. During cleavage (stages 1 and 2), the embryo is located in the center of the egg, surrounded by a layer of yolk cells. After cleavage, the embryo forms a solid, disc-shaped cell cluster. During stage 3, the embryo migrates to the periphery of the egg and acquires bilateral symmetry. The side where it contacts the egg surface corresponds to the future ventral surface of the embryo. Stage 4 is the emergence of the first organ primordia, the brain and pharynx. Gastrulation, as usually defined by the appearance of germ layers, does not exist in Mesos-toma; instead, organ primordia emerge ”in situ” from a mesenchymal mass of cells. Organogenesis takes place during stages 5 and 6. Cells at the ventral surface form the epidermal epithelium; inner cells differentiate into neurons, somatic and pharyngeal muscle cells, as well as the pharyngeal and protonephridial (excretory) epithelium. A junctional complex, consisting initially of small septate junctions, followed later by a more apically located zonula adherens, is formed in all epithelial tissues at stage 6. Beginning towards the end of stage 6 and continuing throughout stages 7 and 8, cytodifferentiation of the different organ systems takes place. Stage 7 is characterized by the appearance of eye pigmentation, brain condensation and spindle-shaped myocytes. Stage 8 describes the fully dorsally closed and differentiated embryo. Muscular contraction moves the body in the egg shell. We discuss Mesostoma embryogenesis in comparison to other animal phyla. Particular attention is given to the apparent absence of gastrulation and the formation of the epithelial junctional complex. Received: 10 February 2000 / Accepted: 10 April 2000     

负子蝽的胚胎发育

负于蝽Sphaerodema rusticus Fabr.的胚胎发育,早期胚带面积大,呈多叶状,明显区分头,颚、胸、腹叶。发育过程需经历胚帝陷入、胚带隆起和胚胎反转三个明显的运动过程。中肠后原基先于前原基形成,并且前、后原基伸展方式不同,使中肠形成不同形态的前、后两部分,两部分的细胞分化亦有差异。神经系统在发育过程中神经节趋于较大程度愈合,腹部的神经节最终愈合为1个复合腹神经节,胸部的神经节也愈合为1个复合胸神经节。本文还总结了胚胎发育时期与卵粒大小的关系,讨论了负子蝽背器官解体的作用。     

Über die entstehung der serosa im besamten und im unbesamten ei von Odontotermes badius hav. (insecta,isoptera)

Zusammenfassung Besamte Eier. Diploide Kerne mit ihren Cytoplasmahöfen gelangen zur Eioberfläche. Das Oberflächencytoplasma wird auf die einzelnen Höfe verteilt. Alle oberflächlich liegenden Zellen wandern aktiv zum Eihinterpol, wo die Keimanlage entsteht. Die Keimanlage setzt sich zusammen aus präsumptiven Keimanlagezellen und prasumptiven Serosazellen. Die Serosakerne werden polyploid, und es laufen nebeneinander diploide und polyploide Mitosen ab. Zur Zeit der Amnionbildung verlassen die spindelformigen Serosazellen den Keimstreif und werden passiv in Richtung auf den Eivorderpol transportiert. Wenn das ganze Ei von Serosazellen umgeben ist, nehmen these erneut an Größe zu.Unbesamtes Ei. Die oberfläehlich liegenden haploiden Zellen wandern aktiv zum Eihinterpol. Jedoch entsteht hier keine Keimanlage, und es wird auch keine Amnionhöhle gebildet. In dem ungeordneten Zellhaufen kommen haploide, diploide und manchmal triploide Metaphase-Platten vor. Diploide und triploide Serosazellen werden zum Eivorderpol verlagert, wo she erneut an Größe zunehmen. Die haploiden Keimanlagezellen degenerieren. Wie im besamten Ei, kommt es auch im unbesamten zu einer Eischwellung.

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The formation of the serosa in fertilized and unfertilized eggs of Odontotermes badius hav. (insecta, isoptera)

Summary The formation of the Serosa in fertilized eggs as follows: Diploid nuclei surrounded by cytoplasm reach the surface of the egg. The cytoplasm on the egg surface is distributed among them. All the single cells now migrate actively to the hind-pole of the egg. There disk-formation and the development of the amnion take place. The disk contains therefore presumptive embryo cells and presumptive serosa cells. The Serosa-nuclei become polyploid and there are sometimes diploid and polyploid mitoses side by side in the disk. At the time of amnion formation the spindle-shaped serosa cells leave the disk and are transported passively backwards by means of local contractions of the yolk-cytoplasm system. Eventually the whole egg is surrounded by serosa cells. At this point the serosa nuclei become larger again and membranes appear between neighbour cells.Unfertilized eggs show the following mode of Serosa formation: On the surface of the egg the haploid cells migrate in the same way as above. But there is no disk formation and no formation of the amnion. The cells form only a disorganized grouping. In this grouping of cells haploid, diploid and sometimes triploid mitoses appear. The diploid and triploid serosa cells are transported to the front part of the egg where they become larger and where membranes appear as described above. The haploid embryo cells degenerate. Fertilized and unfertilized eggs increase in size.

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Herm Professor Dr. Friedrich Seidel zu seinem 75. Geburtstag gewidmet.     

Early embryonic development of the mayfly Ephemera japonica McLachlan (Insecta: Ephemeroptera,Ephemeridae)

In the newly laid egg of the mayfly Ephemera japonica, an egg nucleus (oocyte nucleus) at metaphase of the first maturation division is in the polar plasm at the mid-ventral side of the egg, and a male pronucleus lies in the periplasm beneath a micropyle situated just opposite the polar plasm or at the mid-dorsal side of egg. The maturation divisions are typical. An extensive and circuitous migration of the male pronucleus is involved in the fertilization process: it first moves anteriad in the periplasm from beneath the micropyle to the anterior pole of the egg and then turns posteriad in the yolk along the egg's long axis to the site of syngamy, near the center of the egg. Cleavage is superficial. The successive eight cleavages, of which the first five are synchronized, result in the formation of the blastoderm, and about ten primary yolk cells remain behind in the yolk. Even in the newly formed blastoderm, the thick embryonic posterior half and the thin extraembryonic anterior half areas are distinguished: the former cells are concentrated at the posterior pole of the egg to form the germ disc, and the latter cells become more flattened, forming serosa. Time-lapse VTR observations reveal a yolk stream that is in accord with the migration of the male pronucleus in time and direction. The yolk stream is also generated in activated unfertilized eggs, and it is probable that the migration of the male pronucleus in association with the fertilization may be directed by the yolk stream. J. Morphol. 238:327–335, 1998. © 1998 Wiley-Liss, Inc.