Changes in the structure of Nippostrongylus brasiliensis intestinal cells during development from the free-living to the parasitic stages

The ultrastructure of Nippostrongylus brasiliensis intestinal cells was examined in free-living, feeding second-stage larvae, infective, nonfeeding third-stage larvae, and parasitic, feeding third-stage larvae. The intestinal cells of second-stage larvae were characterized by a well-developed microvillar border, large numbers of ribosomes, Golgi complexes, rough endoplasmic reticulum, and nuclei with prominent nucleoli. The intestinal cells of infective, third-stage larvae had very few microvilli and the cells were extremely narrow. Few ribosomes, Golgi complexes, and little rough endoplasmic reticulum were present. Nuclei did not contain nucleoli. When worms were introduced into an in vitro culture system, development of intestinal cells began. By 36 hr, microvilli were well differentiated and the cysoplasm contained numerous ribosomes and Golgi complexes, and rough endoplasmic reticulum, mitochondria, and nucleoli were prominent. These morphological changes were related to changes in the physiology of Nippostrongylus brasiliensis which occur during development from a free-living to parasitic form.     

Ultrastructural analysis of pathologic lesions in sterol-deficient Nippostrongylus brasiliensis larvae

A variety of cellular lesions were manifested by the free-living larval stages of Nippostrongylus brasiliensis cultured axenically in medium lacking cholesterol. Pathologic changes developed rapidly and were most apparent in intestinal cells which displayed generalized degradation of membranous organelles. Mitochondria, endoplasmic reticulum, and Golgi complexes became disassociated and vacuolated. Autophagosomes appeared within intestinal cells and contained a wide variety of cellular components. By the 5th day gross vacuolization and degeneration of intestinal cells occurred and the hypodermis and lateral cords displayed lysed cytoplasmic regions. The latter structures are concerned with synthesis of cuticle and their degeneration correlates with the suppression of molting and the abnormal molts that occurred.     

The effect of oxygen and carbon dioxide on the development of the free-living stages of Strongyloides ratti in axenic culture

The effect of oxygen and carbon dioxide concentration on the development of the free-living stages of Strongyloides ratti in axenic culture was examined. Hatching of S. ratti eggs was inhibited at very low oxygen levels. Development of all organisms was inhibited in medium gassed with less than 4% O2 in 0.03% CO2 with the remainder N2. Between 8 and 21% O2 there was no significant difference in the percentage developing directly to filariform larvae, free-living females, or free-living males. Cultures gassed with CO2 concentrations greater than 1% in 21% O2 with the remainder N2 manifested inhibited development to filariform larvae, whereas concentrations between 5 and 7.5% enhanced development to free-living females. There was a positive effect on increasing the CO2 concentration from 0.03% to 5% on development to filariform larvae and male worms at levels of 1% and 2% oxygen in nitrogen, respectively. Direction of development, either directly to the filariform larva or to the free-living female, was influenced by CO2 and O2 concentrations encountered by the egg or the newly hatched larva of the parasitic female in axenic culture. The axenic culture system permits an important experimental approach to the study of factors modulating the differentiation of the free-living stages of Strongyloides.     

Subcellular distribution of calcium in zona fasciculata cells of the rat adrenal cortex

Zona fasciculata cells from the adrenal cortex of female Sprague-Dawley rats were fixed by immersion in potassium pyroantimonate-osmium tetroxide and potassium pyroantimonate-glutaraldehyde to study the distribution of calcium. Potassium pyroantimonate-osmium tetroxide treatment gave reproducible patterns of electron-opaque precipitate, whereas inconsistent deposits of reaction product were seen after potassium pyroantimonate-glutaraldehyde fixation. Nuclei showed sparse precipitate over heterochromatin and dense aggregates over areas of nucleoli surrounded by portions of the nucleolar-dense component. Two major cytoplasmic sites of precipitate were identified: mitochondria and vesicles of smooth endoplasmic reticulum. Most of the intramitochondrial precipitate was localized to the intracristal space. Precipitate was also seen in vesicles of Golgi apparatus. The extracellular space was filled with closely packed electron-opaque particles. Observation of tissues treated with control fixative saturated with EGTA showed little if any reaction, confirming that calcium was the primary cation precipitated by potassium pyroantimonate. Our results provide a method suitable for accurate localization of calcium in adrenocortical cells.     

Genital primordium of the free-living marine nematode Halichoanolaimus sonorus (Chromadoria,Chromadorida)

Summary

The genital primordium of the first stage juvenile (J1) of the free-living marine nematode Halichoanolaimus sonorus (Chromadorida: Selachinematidae) was studied using transmission electron microscopy. The primordium consists of four undifferentiated cells: two primordial germ cells (PGC) 5–6 μm in diameter and two somatic cells. The PGC have a large nucleus with nucleolus. The centriole was detected in close vicinity of the PGC nucleus. Most of the cell mitochondria are in close contact with the nuclear envelope. The mitochondria are interspersed by 0.2–0.3 μm particles of an electron-dense diffuse substance devoid of surrounding membrane. Both PGC are closely attached to each other and to the neighboring somatic cells of the genital primordium. The elongated somatic cells contain nuclei devoid of nucleoli; the cytoplasm is filled with free ribosomes and contains occasional cisternae of rough endoplasmatic reticulum (RER), Golgi bodies, mitochondria, and transparent vesicles. The genital primordium is separated by a narrow space from of the intestine (dorsally) and the somatic muscles (ventrally). The PGC of H. sonorous are devoid of typical P granules known for previously studied nematodes as distinct markers of germ line cell lineage. Perinuclear particles of dense diffuse substance found in PGC of H. sonorous could be considered as germ determinants analogous to P granules.     

A post-embedding immunoelectron-microscopic demonstration of apolipoprotein-B-containing lipoprotein particles in hepatocytes of fetal rats

Summary We used the protein-A gold technique to demonstrate the presence of apolipoprotein-B in ultrathin sections of fetal rat liver tissue. It was possible to show for the first time that the electron-dense, osmiophilic particles with diameters of 20–20 nm located within the RER cisternae and Golgi complexes of fetal rat hepatocytes contain apolipoprotein-B components and therefore are lipoproteins. After specific labelling an accumulation of gold label was observed on the RER cisternae, Golgi cisternae and the Golgi-associated secretory vesicles of hepatocytes. The specifity of this labelling pattern was assessed by comparison with cytochemical controls. Our qualitative findings were confirmed by a quantitative analysis of the mean labelling intensity (mean number of gold particles per square micron of the surface area of a particular cellular compartment) on the RER, Golgi complexes, mitochondria, nuclei and the remaining cytoplasm of hepatocytes. It is concluded that the hepatocytes of fetal rats are capable of forming apolipoprotein-B-containing lipoprotein particles. With respect to the size-distribution pattern of the observed intrahepatic lipoprotein particles, we suggest that the hepatocytes of fetal rats produce lipoproteins of the low- and very low-density-lipoprotein type.Abbreviations GA Golgi complex - RER rough endoplasmic reticulum - M mitochondria - N nuclei - LP lipoprotein partieles - L lipid droplet - SV secretory vesicle - BCP blood cell precursor - dm dense intracisternal and intravesicular material - LDL low density lipoproteins - VLDL very low density lipoproteins     

Ultrastructure of the y-organs of Cancer antennarius in normal and de-eyestalked crabs

The paired Y-organs of crustaceans control the molting process. In males of C. antennarius, these glands are opalescent, lobulated, epithelioid structures embedded in brown fatty tissue. Cells in the periphery extend processes to the connective tissue capsule, an arrangement that suggests increased surface area for metabolic exchange. The processes contain mitochondria and are tipped distally with electron dense material. The cytoplasm, scarce relative to nuclear volume, contains vesicles, polymorphic mitochondria with tubular cristae, and numerous free ribosomes, but little in way of smooth or rough endoplasmic reticulum or Golgi complexes. Progressing from intermolt to the premolt stage, mitochondria, as well as vesicles, and electron-dense particles in peripheral processes increase somewhat in number. Also, heterochromatin masses concentrate adjacent to the nuclear envelope. Eyestalk removal, which induces premolt stages in some species, did not produce consistent change in Y-organ substructure in C. antennarius. Although evidence is accumulating that Y-organs secrete a steroid molting hormone during late intermolt-premolt, the substructure of the glands exhibits neither (a) striking changes with the molt cycle, nor (b) all the characteristics typical of vertebrate steroid hormone synthesizing glands. Nevertheless, the structural features, respectively, are consistent with biochemical evidence that Y-organs (a) rapidly take up and convert sterol precursor and secrete a product without its accumulation or change in total sterol pool size, and (b) apparently cannot synthesize the sterol precursor. Y-organ cytology closely resembles that of some vertebrate steroid hormone secreting glands in which this synthetic capacity is minimal.     

Virus-neuron interactions in the mouse brain infected with Japanese encephalitis virus

The virus-host interactions between Japanese encephalitis (JE) virus and mouse brain neurons were analyzed by electron microscopy. JE virus replicated exclusively in the rough endoplasmic reticulum (RER) of neurons. In the early phase of infection, the perikaryon of infected neurons had relatively normal-looking lamellar RER whose cisternae showed focal dilations containing progeny virions and characteristic endoplasmic reticulum (ER) vesicles. The reticular RER, consisted of rows of ribosomes surrounding irregular-shaped, membrane-unbounded cisternae and resembled that observed in JE-virus-infected PC12 cells, were also seen adjacent to the lamellar RER. The appearance of the reticular RER indicated that RER morphogenesis occurred in infected neurons in association with the viral replication. The fine network of Golgi apparatus was extensively obliterated by fragmentation and dissolution of the Golgi membranes and their replacement by the electron-lucent material. As the infection progressed, the lamellar RER was increasingly replaced by the hypertrophic RER which had diffusely dilated cisternae containing multiple progeny virions and ER vesicles. The Golgi apparatus, at this stage, was seen as coarse, localized Golgi complexes near the hypertrophic RER. In the later phase of infection, RER of infected neurons showed a degenerative change, with the cystically dilated cisternae being filled with ER vesicles and virions. Small, localized Golgi complexes frequently showed vesiculation, vacuolation, and dispersion. The present study, therefore, indicated that during the viral replication the normal lamellar RER which synthesized neuronal secretory and membrane proteins was replaced by the hypertrophic RER which synthesized the viral proteins. The hypertrophic RER eventually degenerated into cystic RER whose cisternae were filled with viral products. The constant degenerative change which occurred in the Golgi apparatus during the viral replication suggested that some of the viral proteins transported from RER to the Golgi apparatus were harmful to the Golgi apparatus and that increasing damage to the Golgi apparatus during the viral replication played the principal role in the pathogenesis of JE-virus-infected neurons in the central nervous system.     

The ecdysial gland of the spider crab,Libinia emarginata (L). I. Ultrastructure of the gland in the male

The ecdysial glands of mature male Libinia emarginata are pale, yellowish organs composed of lobes of epithelial cells having oval nuclei which are often eccentric and which have one or two nucleoli containing amorphous granular material and coarse strands. The plasma membrane bordering the basal lamina consists of invaginations containing microtubules which may serve to increase the surface area for metabolic exchange. Masses of smooth endoplasmic reticulum and associated vesicles are scattered throughout the cytoplasm. Two or more vacuoles may coalesce. Larger vesicles lie close to the cell surface. Numerous mitochondria with tubular cristae surround the nucleus and frequently are associated with SER. A few Golgi complexes consisting of flattened sacs, cisternae or vesicles, lipid droplets and free ribosomes were seen. Adjacent plasma membranes may be in close apposition or separated by a space filled with vesicles, granules, or blood or supporting cells. This type of ultrastructure is associated with steroid-secreting cells.     

Species-specific differences in heterogonic development of serially transferred free-living generations of Strongyloides planiceps and Strongyloides stercoralis

The direction of free-living development (homogonic vs. heterogonic) in Strongyloides stercoralis and Strongyloides planiceps was examined by successive transplantation of the uterine eggs of free-living females into a test tube culture system containing fresh feces. The eggs from the first-generation free-living females of S. stercoralis did not develop into second-generation free-living adult worms, but all developed into filariform larvae. However, the majority of S. planiceps eggs from the first-generation free-living females developed into second-generation free-living adults. By successive transfer of uterine eggs of each generation, 9 generations developed, and in every cycle more adult worms developed than filariform larvae. However, the number of free-living generations was not infinite; in experiments repeated twice, the number of worms developing from the eggs of eighth or ninth generations was too small to continue further culture. These findings indicate that the pattern of free-living development is different between the 2 species.     

A post-embedding immunoelectron-microscopic demonstration of apolipoprotein-B-containing lipoprotein particles in hepatocytes of fetal rats

We used the protein-A gold technique to demonstrate the presence of apolipoprotein-B in ultrathin sections of fetal rat liver tissue. It was possible to show for the first time that the electron-dense, osmiophilic particles with diameters of 20-40 nm located within the RER cisternae and Golgi complexes of fetal rat hepatocytes contain apolipoprotein-B components and therefore are lipoproteins. After specific labelling an accumulation of gold label was observed on the RER cisternae, Golgi cisternae and the Golgi-associated secretory vesicles of hepatocytes. The specificity of this labelling pattern was assessed by comparison with cytochemical controls. Our qualitative findings were confirmed by a quantitative analysis of the mean labelling intensity (mean number of gold particles per square micron of the surface area of a particular cellular compartment) on the RER, Golgi complexes, mitochondria, nuclei and the remaining cytoplasm of hepatocytes. It is concluded that the hepatocytes of fetal rats are capable of forming apolipoprotein-B-containing lipoprotein particles. With respect to the size-distribution pattern of the observed intra-hepatic lipoprotein particles, we suggest that the hepatocytes of fetal rats produce lipoproteins of the low- and very low-density-lipoprotein type.     

Ultrastructural characteristics of insect corpora allata in relation to larval diapause

Summary The ultrastructure of active and inactive corpora allata from last instar larvae of the southwestern corn borer, Diatraea grandiosella, was examined. Active glands were obtained from pre-, early, and mid-diapausing larvae; inactive ones from late and non-diapausing larvae. Each gland contains 13 to 18 cells which have the following common features: well developed smooth endoplasmic reticulum, scattered rough endoplasmic reticulum and free ribosomes, microtubules, vacuolated nucleoli, and interlocking plasma membranes. The gland contains intercellular deposits, and is supplied by regular and neurosecretory axons.Special ultrastructural features of the corpus allatum from the five groups of larvae examined were as follows: pre-diapause: extensive vesicular smooth endoplasmic reticulum, numerous cup-shaped mitochondria and Golgi bodies with stacked cisterns and vesicles, few small lipid droplets, large nuclei with dispersed chromatin, absence of lysosomes; early diapause: stacked, whorled, and vesicular smooth endoplasmic reticulum of equal abundance, numerous rod-shaped mitochondria, some Golgi bodies but without distinct stacks of cisterns, few lipid droplets and lysosomes, chromatin dispersed and also attached to the nuclear envelope; mid-diapause: similar to early diapause except for the presence of more stacked, smooth endoplasmic reticulum, chromatin in large chunks mostly attached to the nuclear envelope; late diapause: whorled smooth endoplasmic reticulum and rod-shaped mitochondria predominating, complicated Golgi bodies with stacks of cisterns and large empty sacs, few large lipid droplets, some lysosomes containing mainly whorled bodies, chromatin in large chunks attached to the nuclear envelope; non-diapause: similar to late diapause except for less extensive smooth endoplasmic reticulum, more abundant mitochondria, fewer intercellular deposits. Although these observations suggest that the smooth endoplasmic reticulum, and possibly mitochondria, and Golgi bodies are involved in juvenile hormone production, specific sites of synthesis or storage of the hormone were not revealed.Supported in part by grant no. PCM 74-18155 A01 from the National Science Foundation. Contribution from the Missouri Agricultural Experiment Station as journal series no. 8234. We thank Ms. L. Yin for her skillful assistance, and Dr. M.F. Brown of the College of Agriculture Electron Microscope Facility for his advice and the use of equipment.     

The mode of action of acute and chronic concentrations of waterborne Cd in the digestive gland of the acclimated infested freshwater crab (<Emphasis Type="Italic">Potamonautes warreni</Emphasis>)

Cadmium (Cd) uptake, transport and accumulation were investigated in the digestive gland of the freshwater crab, Potamonautes warreni, acclimated in its natural habitat to stresses, such as microbial gill infestations, Cd(2+) and NH(4)(+), and subsequently exposed to increasing concentrations of Cd in the laboratory for up to 21 days. Cd exposure (0.2 mg l(-1)) for 7-14 days led to Cd permeating cell membranes in a particulate form; it was adsorbed intracellularly to endocytotic circulating amoebocytes, lipid droplets and Golgi vesicles in R-cells. Cd also caused dissociation of the fibrillar rough endoplasmic reticulum (RER) and an increase in phagocytotic activity in F- and B-cells. After 21 days, Cd accumulated as crystal deposits on the basal membranes of cells in the haemolymph space and along the microvilli of cells lining the tubular lumen. Elevated Cd concentrations were found in the cytosol, amoebocytes, Golgi vesicles and P/Ca granules in R-cells. Chronic exposure to higher concentrations of Cd (0.5 and 1.0 mg l(-1)) increased crystal deposition, whereas concentrations of Cd, copper and iron decreased in the cell membranes and in amoebocytes and increased in Golgi vesicles. Reduced lipid content, swollen nuclei with vesiculated nucleoli and enhanced activity of RER in R-cells were also noted. Cd was stored in the P/Ca and Ca granules of B-cells. Acute exposure to Cd (2.0 mg l(-1) for 48 h) caused metal granule accumulation along cells lining the tubular lumen and cellular dissociation, with acidosis and necrosis in the cytoplasm and Cd deposits in mitochondria. Cd accumulated in the cells of the digestive gland in a time-, concentration- and cell-type-specific fashion.     

The fine structure of the carapace integument of Daphnia magna straus (Crustacea branchiopoda)

Summary The structure of the two integumental layers comprising the carapace of female D. magna was examined at several points through the molt cycle. The epicuticle and procuticle are simple in organisation; pore canals are absent but intracuticular fibres are present, forming complexes with invaginations of the epidermal plasma membrane similar to such complexes described in the literature for other arthropods. The epidermis consists almost entirely of cuticle-secreting cells. Secretion of the new cuticle begins when 50–67% of the instar has elapsed by which time the epidermal cells have increased in height and their nuclei have become more rounded. However, other presumed secretory phenomena observed viz. the formation of dense core vesicles by Golgi bodies, and the occurrence of these and coated vesicles near the apical plasma membrane are not restricted to any particular period during the molt cycle. This suggests that the mechanisms of cuticle secretion do not undergo marked changes in activity as they do in decapods; presumably this relative continuity is related to the much shorter molt cycle of cladocerans.The technical assistance of G.A. Bance, and the financial support provided by the National Research Council of Canada are gratefully acknowledged     

The physical association between rat liver mitochondria and rough endoplasmic reticulum : I. Isolation, electron microscopic examination and sedimentation equilibrium centrifugation analyses of rough endoplasmic reticulum-mitochondrial complexes

Rough endoplasmic reticulum-mitochondrial (RER-MT) complexes have been isolated from rat liver homogenates by rate zonal Centrifugation using a reorienting zonal rotor. Electron microscopic examination of the isolated complexes reveals a close association between rough endoplasmic reticulum (RER) and mitochondria. The associated RER appears as bilamellar sheets as it does in intact liver tissue, not as microsomal vesicles. When the complexes are subjected to sedimentation equilibrium Centrifugation, the marker enzymes for mitochondria and RER coband at an equilibrium density of 1.190. Electron microscopic analysis of the complexes after sedimentation equilibrium Centrifugation again reveals a close association between RER and mitochondria. Treatment of the complexes with 500 mM KCl or 500 mM KCl plus 20 mM EDTA resulted in a shift in the equilibrium density of the complexes to 1.180 and 1.176, respectively. Concomitant with the density shift was a release of A₂₆₀ units to the top of the gradient. After incubating KCl-EDTA stripped complexes with cytoplasmic ribosomes and ribosomal subunits, the complexes band at the same equilibrium density, 1,190, as do untreated complexes. In order to completely remove the associated RER it is necessary to treat the complexes with digitonin at a concentration of 0.13 mg digitonin/mg protein. Our data suggest that a fraction of the total cellular RER is physically associated with rat liver mitochondria.     

Morphological effects of brefeldin A on the intracellular transport of secretory materials in parotid acinar cells

The morphological effects of Brefeldin A (BFA) on the parotid acinar cells of a rat were investigated at the stage of active resynthesis of secretory materials following administration of the secretogogue, isoproterenol. Incubation with BFA resulted in: a) marked dilation of the rough endoplasmic reticulum (RER), b) involution of the Golgi complex to rudimentary forms which disseminated throughout the cytoplasm, and c) agenesis of secretion granules. It appears that the primary action of BFA is inhibition of the export of secretory materials from the RER toward the Golgi complexes. Histochemical staining indicated the thiamine pyrophosphatase (TPPase) positive saccules of the Golgi stack to undergo degradation in autophagic vacuoles. In contrast, small vesicles showing the osmium reducing activity characteristic of cis elements, including osmium negative vesicles, continued to be present throughout a 4-h period of investigation, indicating the cis and, most likely, medial elements to be the components of the rudimentary Golgi complexes. On removal of the drug, a large number of transport vesicles appeared immediately from the RER and carried secretory materials to the rudimentary Golgi complex, so that the organelles were rapidly reconstructed within 30-60 min, followed by the reaccumulation of secretory granules by 90 min. It is thus indicated that the size and configuration of the Golgi complex is regulated by a dynamic equilibrium of the transport of secretory materials, and that the rudimentary Golgi complex containing cis and probably medial elements may function as the smallest units of the Golgi complex for full development as seen under normal conditions.     

Synthesis and transport of the organic matrix of the spicules in the gorgonian Leptogorgia virgulata (Lamarck) (Coelenterata: Gorgonacea)

Summary The sequence of the synthesis and transport of the organic matrix of spicules has been elucidated in the gorgonian Leptogorgia virgulata by use of ³H-aspartic acid as the tracer in electron-microscopic autoradiography. The entire process of matrix synthesis and transport takes approximately 2 h. It seems that the protein moiety of the organic matrix is synthesized in the RER prior to 5 min following the initial 10 min incubation in the tracer. At the 5 min chase the label is moving from the RER to the Golgi complexes where the carbohydrate moiety of the matrix is presumed to be synthesized. At the 5 to 15 min chases the label is transported out of the Golgi complexes via Golgi vesicles. This phase continues for 30 min. From 60 to 120 min the ³H-aspartic acid moves to the spicules. After 120 min the majority of the label has moved into the spicules. Silver grain counts over both multivesicular and electron-dense bodies remain at relatively low and constant levels over 4 h indicating that neither organelle is involved in the synthesis and transport of the organic matrix.Contribution No 512; Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, South Carolina 29208, USA     

Ultrastructure of the supporting cells of the paratympanic organ in the chicken: a preliminary study

Electron microscopic studies reveal that the supporting cells of the paratympanic organ in the chicken have a fine structure characterised by mitochondria, RER and a well developed Golgi apparatus; furthermore, several vesicles with a clear content can be observed in the apical cytoplasm. The ultrastructure of supporting cells indicates high metabolic activity. The possible metabolic and mechanical function of the supporting cells are discussed.     

Ultrastructure of the lateral organs in larvalArgas (Persicargas) arboreus (Ixodoidea: Argasidae)

The ultrastructure of lateral organs (LO) in the larval tickArgas (Persicargas) arboreus is described before and after feeding and up to the 1st day of moulting. Three pairs of LO are associated with three pedal nerves arising from the synganglion. In unfed ticks, each LO is ensheathed by a neural lamella and consists of 6–7 neuronal cell bodies; their cytoplasm is mostly occupied by cisternae of rough endoplasmic reticulm (RER). In fully engorged ticks, the enlarged neuronal cells contain vacuolar cisternae of smooth endoplasmic reticulum (SER), coated vesicles and mitochondria. Golgi bodies are involved in the formation of neurosecretory granules which dominate, with the SER vacuoles, the cell cytoplasm before moulting. The vacuoles, coated vesicles and neurosecretory granules are similar to those found in the vertebrate steroid-secreting cells. Condensing vacuoles may fuse with lysosome-like bodies to form larger ones; these are possibly responsible for the cell breakdown when secretory products are no longer required. Ultrastructural observations of LO suggest that they are neuroendocrine glands and that, in engorged larvae, they may secrete a hormone involved in the control of moulting.     

Previtellogenic development and vitellogenin synthesis in the fat body of a mosquito: an ultrastructural and immunocytochemical study

We describe two phases, previtellogenic and vitellogenic, in the activity of the trophocytes in the fat body of the mosquito Aedes aegypti. The previtellogenic phase, leading to trophocyte competence to synthesize vitellogenin (Vg), occurred during the first 3 days after eclosion. This phase was characterized by enlargement and activation of the nucleoli, proliferation of ribosomes and rough endoplasmic reticulum (RER), development of Golgi complexes, and extensive invaginations of the plasma membrane. During the vitellogenic phase, initiated by a blood meal, Vg was first detected, by immunofluorescence, 1 hr after feeding. The intensity of the immunoreaction increased for the next 24 hr, was declining at 30 hr, and had disappeared by 48 hr. Vg synthesis was characterized ultrastructurally by the enlargement of the RER and the formation of dense secretion granules in Golgi complexes. These secretion granules were two to three times larger at the peak of Vg synthesis than at the beginning. The granules discharged their contents by exocytosis. Two electron microscopical immunocytochemical methods, immunoferritin and peroxidase-antiperoxidase, confirmed this pathway of Vg processing. For the first 12 hr after feeding. Vg synthetic organelles proliferated and the active nucleoli were multilobed; thereafter, while Vg synthesis continued, the nucleoli began to regress into compact bodies. Termination of Vg synthesis was marked by autophagical degradation of Vg synthetic and processing organelles.