Conditions de production et de conservation D'Ageniaspis fuscicollis var.Praysincola,pour son utilisation en lutte biologique

Résumé Il est possible d'éleverAgeniaspis fuscicollis Dalm. sur un h?te de substitution,Acrolepia assectella Zeller, et de conserver les chrysalides parasitées afin d'étaler la production. L'activité de ponte du parasite est soutenue entre 13°C et 33°C. Le fait de multiplier cet hyménoptère sur un h?te de substitutio, lui-même aliment sur milieu artificiel, ne semble pas modifier son comportement au laboratoire.

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Summary It is possible to rearAgeniaspis fuscicollis Dalm on the alternative host,Acrolepia assectella Zeller and to preserve the parasitized host pupae at a low temperature so that the production is spread over. The egg laying activity is high beetween 13°C and 33°C. Apparently, the rearing of the hymenoptera on an alternative host being fed on an artificial diet doesn't modify its behaviour in the laboratory.

     

Seasonal phenology and stage-specific parasitism of the apple ermine moth, Yponomeuta malinellus Zeller, in Korea

The apple ermine moth, Yponomeuta malinellus Zeller (Lepidoptera: Yponomeutidae), is a tent caterpillar that feeds on Malus spp. in Korea. Populations of the moth in native areas appeared to be regulated by the assemblage of parasitoids. Phenological associations between host stages and parasitoids, susceptible stage(s) of the host for each parasitoid, and stage‐specific parasitism were studied. The egg larval parasitoid Ageniaspis fuscicollis (Dalman) had highest parasitism of first instar larvae (24%), with 14% parasitism of other larval stages. Dolichogenidea delecta (Haliday) was recovered from all larval instars with the highest parasitism rate of second instar larvae (20.1%), followed by 19.9% parasitism of mid‐larval hosts. Herpestomus brunicornis Gravenhorst was reared from second instar larvae through to pupal collection, and had the highest parasitism rate (29.9%) at the pupal stage. The larval pupal parasitoid Zenillia dolosa (Meigen) was recovered from mid‐larval to pupal stages with the highest parasitism rate (5.5%) occurring in third to fourth instar larvae. The host stages for developing A. fuscicollis completely overlap with those of D. delecta, and with those of H. brunicornis to some degree. A statistically significant negative correlation exists between A. fuscicollis and these dominant parasitoids, indicating competitive interaction within the host.     

Pre‐Patch Experience Affects the Egg Distribution Pattern in a Polyembryonic Parasitoid of Moth Egg Batches

According to foraging theory, female parasitoids should alter their host choice in response to cues that indicate a limitation of resources. We tested whether females of the polyembryonic parasitoid Ageniaspis fuscicollis (Hymenoptera: Encyrtidae), which attack egg batches of small ermine moths (Lepidoptera: Yponomeutidae), would alter their host acceptance pattern in response to different pre‐patch experience. We kept females of the parasitoid prior to a patch visit under different conditions, which should indicate different levels of competition for hosts. With increased competition as pre‐patch experience, females laid more eggs per host egg and self‐superparasitized more often, and the resultant egg distributions showed a trend from more regular distributions to increasingly Poisson and aggregated distributions. Consequently, females with a pre‐patch experience that would indicate low competition for hosts had the most even egg distributions. We conclude that pre‐patch experience of competitors may lead to a significant change of mutual interference patterns in egg‐laying A. fuscicollis wasps.     

Morphology,ultrastructure, and development of the parasitic larva and its surrounding trophamnion of Polypodium hydriforme Ussov (Coelenterata)

Summary The larval stage of Polypodium hydriforme is planuliform and parasitic inside the growing oocytes of acipenserid fishes. The larva has inverted germ layers and a special envelope, the trophamnion, surrounding it within the host oocyte. The trophamnion is a giant unicellular provisory structure derived from the second polar body and performing both protective and digestive functions, clearly a result of adaptation to parasitism. The trophamnion displays microvilli on its inner surface, and irregular protrusions anchoring it to the yolk on its outer surface. Its cytoplasm contains long nuclear fragments, ribosomes, mitochondria, microtubules, microfilaments, prominent Golgi bodies, primary lysosomes, and secondary lysosomes with partially digested inclusions.The cells of the larva proper are poorly differentiated. No muscular, glandular, neural, interstitial, or nematocyst-forming cells have been found. The entodermal (outer layer) cells bear flagella and contain rough endoplasmic reticulum; the ectodermal (inner layer) cells lack cilia and contain an apical layer of acid mucopolysaccharid granules. The cells of both layers contain mitochondria, microtubules, and Golgi bodies; their nuclei display large nucleoli with nucleolonema-like structure, decondensed chromatin, and some perichromatin granules. At their apical rims, the ectodermal cells form septate junctions; laterally, the cells of both layers form simple contacts and occasional interdigitations. The lateral surfaces of entodermal cells are strengthened by microtubules.     

Altération du développement et élimination de l'entomophage polyembryonnaire,Ageniaspis fuscicollis [Hym: Encyrtidae] Par le jeûne de son hôte,Hyponomeuta malinellus [Lep.: Hyponomeutidae]

Résumé Les chenilles d'Hyponomeuta malinellus Zell. sont soumises à différents stades de leur développement à un je?ne expérimental qui se produit parfois au cours du cycle naturel et notamment lors des phases de gradation du phytophage. Le je?ne de l'h?te affecte plus ou moins fortement le développement de son parasite polyembryonnaireAgeniaspis fuscicollis Thoms., selon le stade atteint par cet entomophage au début de la spoliation imposée. C'est au stade morulaire correspondant à une des phases de multiplication asexuée de la polyembryonie que le parasite se révèle le plus vulnérable. Les populations de l'h?te et du parasite sont le plus souvent inégalement affectées par les conditions imposées; cette ?sensibilité différente? peut constituer un elément nouveau dans la dynamique de la coaction h?te-parasite.

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Summary The caterpillars ofHyponomeuta malinellus Zell. are subjected at different stages during their development to an experimental fast which sometimes happens during the normal period and most particularly during the phases of gradation of the host. The fast of the host affects more or less strongly the development of its polyembryonic parasiteAgeniaspis fuscicollis Thoms according to the stage reached by this entomophage at the beginning of the imposed spoliation. It is at the morula stage corresponding to one of the asexual phases of multiplication of the polyembryony that the parasite is at its most vulnerable. The populations of the host and parasite are most often unequally affected by the imposed conditions; this different sensitivity can constitute a new element in the dynamics of the coaction hostparasitoid.

     

The ultrastructure of the spermatheca of Biomphalaria glabrata (gastropoda,pulmonata)

A study of the ultrastructure of the spermatheca of virgin freshwater snails Biomphalaria glabrata, kept in isolation since hatching, and in freely mating individuals maintained in colonies, shows that the spermatheca, an accessory organ of the female genital tract of pulmonate snails, is a pear-shaped blind pocket, lined with a single-layered columnar epithelium, surrounded by a thin muscle and pigmented connective. The apex of each epithelial cell may be ciliated, whereas the basis lies on a thick basement membrane. In virgin snails the spermatheca is smaller, its lumen contains a gelatinous, amorphous material; the apex of the epithelial cells contains many mitochondria but few granules. The nucleus appears in the basal third of the cell, topped by the Golgi complex and endoplasmic reticulum elements. In snails which have mated, the spermatheca is swollen, with a somewhat distended lower epithelium; its lumen contains numerous spermatozoa, in various degrees of degradation, which increases with the passage of time after copulation. The apex of the epithelial cells becomes very rich in granules with varied content, including multivesicular bodies. The latter are apparently exocytosed. Pinocytosis occurs at the base of microvilli. Glycogen can be seen accumulating in some cells. Tubular structures, ca. 60 nm in diameter, arranged regularly within the endoplasmic reticulum elements, could occasionally be seen at the basal part of the epithelial cells. It is suggested that the multivesicular bodies may contain enzymes which are secreted to the lumen. The partially digested sperm material would then be absorbed by micropinocytosis, and further digested in the secondary phagosomes at the apical portion of the epithelium.     

Introduction and establishment of parasitoids for the biological control of the apple ermine moth, Yponomeuta malinellus (Lepidoptera: Yponomeutidae), in the Pacific Northwest

Four parasitoids were imported from five countries in Eurasia and released in northwestern Washington, US, to control the apple ermine moth (AEM), Yponomeuta malinellus Zeller, which colonized the Northwest around 1981. From 1988 to 1991, 95,474 individuals of Ageniaspis fuscicollis (Dalman) from France, China, Korea, and Russia were released in Washington. Parasitism of AEM increased 4- to 5-fold over that produced by preexisting natural enemies between 1989 and 1994 at 22 monitored sites. Subsequently, the wasp dispersed up to 20 km from release sites. A. fuscicollis also parasitized the cherry ermine moth, Yponomeuta padellus (L.), which was discovered in the Pacific Northwest in 1993. A total of 1813 individuals of Herpestomus brunnicornis (Gravenhorst) from France, Korea, and Japan were released in 1989–1991, and 26 wasps were recovered in 1994–1995. From 1989 to 1991, 2647 Diadegma armillata (Gravenhorst) individuals from France were released. D. armillata was recovered at one site in 1991 two months following release, but no other recoveries have been made. A total of 8274 Eurystheae scutellaris(Robineau-Desvoidy) individuals were released in 1989 to 1991. However, this tachinid has not been recovered. A consistent decline of AEM populations occurred in 1989–1995, including at sites where A. fuscicollis was not recovered, suggesting other factors also contributed to this pest’s decline. Now well established in western Washington, A. fuscicollis may help suppress future outbreaks of Y. malinellus and its congener, Y. padellus.     

Fine structure of the developing oocytes in adultArgas (Persicargas) arboreus (Ixodoidea: Argasidae)

The structure of the developing oocytes in the ovary of unfed and fed femaleArgas (Persicargas) arboreus is described as seen by scanning (SEM) and transmission (TEM) electron microscopy. The unfed female ovary contains small oocytes protruding onto the surface and its epithelium consists of interstitial cells, oogonia and young oocytes. Feeding initiates oocyte growth through the previtellogenic and vitellogenic phases of development. These phases can be observed by SEM in the same ovary.The surface of isolated, growing oocytes is covered by microvilli which closely contact the basal lamina investing the ovarian epithelium and contains a shallow, circular area with cytoplasmic projections and a deep pit, or micropyle, at the epithelium side. In more advanced oocytes the shell is deposited between microvilli and later completely covers the surface.Transmission EM of growing oocytes in the previtellogenic phase reveals nuclear and nucleolar activity in the emission of dense granules passing into the cytoplasm and the formation of surface microvilli. The cell cytoplasm is rich in free ribosomes and polysomes and contains several dictyosomes associated with dense vesicles and mitochondria which undergo morphogenic changes as growth proceeds. Membrane-limited multivesiculate bodies, probably originating from modified mitochondria, dictyosomes and ribosomal aggregates, are also observed. Rough endoplasmic reticulum is in the form of annulate lamellae. During vitellogenesis, proteinaceous yolk bodies are formed by both endogenous and exogenous sources. The former is involved in the formation of multivesicular bodies which become primary yolk bodies, whereas the latter process involves internalization from the haemolymph through micropinocytosis in pits, vesicles and reservoirs. These fuse with the primary yolk bodies forming large yolk spheres. Glycogen and lipid inclusions are found in the cytoplasm between the yolk spheres.     

Larval parasitoids of the apple ermine moth, <Emphasis Type="Italic">Yponomeuta malinellus</Emphasis>in Korea,Japan, and China

Larval parasitoids of Yponomeuta malinellus Zell. (Lepidoptera: Yponomeutidae), the apple ermine moth (AEM), were sought in northeast Asia with the goal of identifying potential biological controls of the moth, which appeared to threaten the apple industry in Washington State, USA during the 1980s. Ten primary and four secondary parasitoids were found. Dolichogenidea delecta (Haliday) (Braconidae), Ageniaspis fuscicollis (Dalman) (Encyrtidae), Herpestomus brunnicornis Grav. (Icheumonidae), Bessa paralella (Meigen), and Zenillia dolosa (Meigen) (Tachinidae) were the most important parasitoids. The composition of parasitoid species was more diverse in Korea and Japan than in China; two species were found in China, compared to nine in Korea and seven in Japan. A. fuscicollis caused a greater mortality in all investigated countries; 22.7, 11.0, and 9.3% in China, Korea, and Japan, respectively. There was a high similarity in the composition of the parasitoid complex between Korean and Honshu populations but the rates of parasitization were different. The polyphagous B paralella caused significantly higher parasitism in Honshu (18.2%) than in Korea (0.5%). In contrast, H. brunnicornis caused significantly higher parasitism in Korea (8.7%) than in Japan (2.4%). A. fuscicollis and H. brunnicornis, judged to be the most appropriate parasitoids for biological control of AEM moth in the USA, were collected and sent to the USA for release. A. fuscicollis established and is contributing to the control of AEM.     

The Fine Structure of Conidophrys pitelkae Bradbury Related to its Life Cycle and Taxonomic Position in the Apostomatida1

Electron microscopy of the tomite of Conidophrys pitelkae confirms that Jankowski was correct in including the pilisuctorians in the Apostomatida. Like other apostome tomites, the tomite of Conidophrys possesses a rosette opening to the exterior, kinetodesmata made up of stacks of individual kinetodesmal fibrils, and canaliculi that are surrounded by dense inclusion bodies and open on the ventral surface. The fine structure of the trophont of Conidophrys, however, is quite unlike that of other apostome trophonts. The elaborate infraciliature of the tomite disappears immediately after it settles and reappears de novo on the trophont just before tomitogenesis. The cyst wall, which completely encloses the trophont and grows with it, attaches the ciliate to a seta on its, host, the shrimp Crangon crangon. The setae on which tomites settle vary greatly in size and shape, but each appears to have at its tip some digitiform cuticular projections that surmount a pore, which opens into the lumen of the seta. The trophont's only direct connection to its host is at the cytostome, a unique structure formed of delicate tubules that pass through the pore into the lumen of the seta. Ingestion is by micropinocytosis, and there are no visible food reserves.     

On the ultrastructure of differentiating secondary xylem in willow

Summary Studies of differentiating xylem inSalix fragilis L. show the immediate cambial derivatives to be ultrastructurally similar. The Golgi apparatus is important at all stages of wall synthesis, possibly producing (amongst other substances) hemicellulose material which is carried to the wall in vesicles or multivesicular bodies. The endoplasmic reticulum also contributes one or more components to the developing wall: at some stages during differentiation the endoplasmic reticulum produces electron opaque bodies which appear to be guided towards the wall by microtubules. Compact structures formed from concentric membranes (myelin-like bodies) have been found joined to rough endoplasmic reticulum, but their presence is not explained.Two types of plasmalemma elaboration occur: invagination of the plasmalemma itself to form vesicles which may contain cytoplasmic material; and vesicles between the plasmalemma and cell wall which are the result of single vesicles or multivesicular bodies traversing the plasmalemma. Both systems provide a means for transporting cytoplasmic material across the plasmalemma.Microtubules have been seen associated with all vesicles derived from the cytoplasm which appear to be moving towards the wall. The presence of microtubules may generally be explained in terms of orientation of vesicles, even if they also happen coincidentally to parallel the supposed orientation of microfibrils in the wall itself. It is possible to resolve connections between the microtubules and the plasmalemma.     

Sperm development in the teleost Oryzias latipes

Summary In Oryzias latipes the processes of spermatogenesis and spermiogenesis occur within testicular or germinal cysts which are delimited by a single layer of lobule boundary cells. These cells, in addition to comprising the structural component of the cyst wall, ingest residual bodies cast off by developing spermatids. Therefore, they are deemed to be the homologue of mammalian Sertoli cells. The germ cells within a cyst develop synchronously owing to the presence of intercellular bridges connecting adjacent cells. Since bridges also connect spermatogonia, it seems probable that all of the germ cells within a cyst may form a single syncytium and do not exist as individual cells until the completion of spermiogenesis when the residual bodies are cast off. Significant differences between spermiogenesis in O. latipes and in the related poeciliid teleosts are discussed.     

Arabinogalactan-rich glycoproteins are localized on the cell surface and in intravacuolar multivesicular bodies

We investigated the subcellular distribution of antigenic sites immunoreactive to the monoclonal antibody 16.4B4 (PM Norman, VPM Wingate, MS Fitter, CJ Lamb [1986] Planta 167: 452-459) in tobacco (Nicotiana tabacum) leaf cells. This antibody is directed against a glycan epitope in a family of plasma membrane arabinogalactan proteins of 135 to 180 kilodaltons, elaborated from a polypeptide of relative molecular mass 50 kilodaltons (PM Norman, P Kjellbom, DJ Bradley, MG Hahn, CJ Lamb [1990] Planta 181: 365-373). We demonstrated by immunogold electron microscopy that the epitope reactive with monoclonal antibody 16.4B4 is localized on the cell surface in the leaf parenchyma cell periplast. The 16.4B4 antigen is also localized in multivesicular invaginations of the plasma membrane also known as plasmalemmasomes, implying a biochemical and, hence, functional interrelationship between these structures. Monoclonal antibody 16.4B4 also labels intracellular multivesicular bodies that appear to represent internalized plasmalemmasomes. Antibody reactivity was also observed in partially degraded multivesicular bodies sequestered within the central vacuole. We propose that the subcellular distribution of the epitope reactive with monoclonal antibody 16.4B4 defines a plasmalemmasome (or multivesicular body-mediated) pathway for the internalization of the periplasmic matrix for vacuolar mediated disposal. The multivesicular bodies appear to be equivalent to the well-characterized endosomes and multivesicular bodies of animal cells involved in the internalization and lysosome-mediated degradation of extracellular materials.     

The ultrastructure of oogenesis and yolk formation in Labidocera aestiva (Copepoda: Calanoida)

Yolk formation in the oocytes of the free-living, marine copepod, Labidocera aestiva (order Calanoida) involves both autosynthetic and heterosynthetic processes. Three morphologically distinct forms of endogenous yolk are produced in the early vitellogenic stages. Type 1 yolk spheres are formed by the accumulation and fusion of dense granules within vesicular and lamellar cisternae of endoplasmic reticulum. A granular form of type 1 yolk, in which the dense granules within the cisternae of endoplasmic reticulum do not fuse, appears to be synthesized by the combined activity of endoplasmic reticulum and Golgi complexes. Type 2 yolk bodies subsequently appear in the ooplasm but their formation could not be attributed to any particular oocytic organelle. In the advanced stages of vitellogenesis, a single narrow layer of follicle cells becomes more developed and forms extensive interdigitations with the oocytes. Extra-oocytic yolk precursors appear to pass from the hemolymph into the follicle cells and subsequently into the oocytes via micropinocytosis. Pinocytotic vesicles fuse in the cortical ooplasm to form heterosynthetically derived type 3 yolk bodies.     

Germ-line cysts are formed during oogenesis in Erpobdella octoculata (Annelida,Clitellata, Erpobdellidae)

Abstract

Erpobdella octoculata (Clitellata, Hirudinea, Erpobdellidae) has paired ovarian sacs, each containing several rod-shaped structures termed ovarian bodies. Oogenesis takes place within the ovarian bodies. We show that in the apical part of the bodies the germ-line cells form syncytial cysts of cells interconnected by stable intercellular bridges. Germ-line cyst architecture is broadly similar to that of other clitellate annelids; that is, each germ cell has only one intercellular bridge connecting it to the anuclear cytoplasmic mass, the cytophore. Unlike germ-line cysts described in other leech species, the cytophore in cysts of E. octoculata is poorly developed, taking the form of thin cytoplasmic strands. Oogenesis in E. octoculata is meroistic because the germ cells forming the cysts (cystocytes) have diverse fates, i.e., nurse cells and oocytes appear. One large ramified cell (apical cell) occurs within the apical part of the ovarian body. We compare the ultrastructure of the apical cell found in E. octoculata with that of apical cells described recently in some hirudiniform leeches. The germ-line cysts as well as the oocytes are enveloped by somatic follicular cells. As in other leeches, the follicular cells surrounding the growing oocytes have cytoplasm perforated by intracellular canals. In view of the many similarities between E. octoculata ovarian bodies and the ovary cords described in glossiphoniids and especially in hirudiniform leeches, we suggest that the ovarian bodies found in E. octoculata are in fact modified ovary cords.     

Receptor-mediated and adsorptive endocytosis by male germ cells of different mammalian species

Summary The routes for adsorptive and receptor-mediated endocytosis were studied in vivo after microinjection of tracers into the lumen of the seminiferous tubules, and in vitro in isolated germ cells of different mammals. Cationic ferritin was located on the plasma membrane, in vesicles, in tubules, in multivesicular bodies and in lysosome-like granules of mouse spermatocytes. In these cells the number of multivesicular bodies varied during spermatogenesis. Spermatids and to a lesser extent residual bodies also performed adsorptive endocytosis. In the rat and monkey (Macaca fascicularis) diferric transferrin was specifically taken up by germ cells via receptor-mediated endocytosis. The labelling was observed subsequently in membrane pits, vesicles, endosome-like bodies and pale multivesicular bodies. A progressive decrease in the frequency of the labelling of the germ cells by transferrin-gold particles was observed from spermatogonia to spermatocytes and to early spermatids, which could indicate that iron is particularly required by germ cells during the mitotic and meiotic processes. Adsorptive and receptor-mediated endocytosis therefore occurs in all classes of germ cells. These endocytic processes are most probably required for germ cell division, differentiation and metabolism.     

The fine structural localization of acid phosphatase in the gut epithelial cells of the slug,Avion ater (L.)

Summary Acid phosphatase, generally thought of as a lysosomal enzyme and indeed widely employed as a lysosomal marker, has been found associated with the Golgi complex of all cell types from the crop, intestine and digestive gland ofArion ater. Reaction product was also detected within the multivesicular bodies and cytoplasm of columnar cells from the crop and the multivesicular bodies of mucous cells from the intestine. A vacuolar localization was obtained in the digestive cells of the intestine and digestive gland. Secretory protein granules in the calcium cells of the same gland and apical vacuoles in the so-called thin cells also showed a positive reaction.This work was undertaken as part of a slug research project under the direction and co-ordination of Dr. D. K.Roach, supported by A.R.C. Assistance was given by Mr. T. R.Mainwaring in the preparation of tissue for electron microscopy.I would like to thank Professor J.Brough and Professor D.Bellamy for providing facilities and encouragement.     

Macropinocytosis is the endocytic pathway that mediates macrophage foam cell formation with native low density lipoprotein

Previously, we reported that fluid-phase endocytosis of native LDL by PMA-activated human monocytederived macrophages converted these macrophages into cholesterol-enriched foam cells (Kruth, H. S., Huang, W., Ishii, I., and Zhang, W. Y. (2002) J. Biol. Chem. 277, 34573-34580). Uptake of fluid by cells can occur either by micropinocytosis within vesicles (<0.1 microm diameter) or by macropinocytosis within vacuoles ( approximately 0.5-5.0 microm) named macropinosomes. The current investigation has identified macropinocytosis as the pathway for fluid-phase LDL endocytosis and determined signaling and cytoskeletal components involved in this LDL endocytosis. The phosphatidylinositol 3-kinase inhibitor, LY294002, which inhibits macropinocytosis but does not inhibit micropinocytosis, completely blocked PMA-activated macrophage uptake of fluid and LDL. Also, nystatin and filipin, inhibitors of micropinocytosis from lipid-raft plasma membrane domains, both failed to inhibit PMA-stimulated macrophage cholesterol accumulation. Time-lapse video phase-contrast microscopy and time-lapse digital confocal-fluorescence microscopy with fluorescent DiI-LDL showed that PMA-activated macrophages took up LDL in the fluid phase by macropinocytosis. Macropinocytosis of LDL depended on Rho GTPase signaling, actin, and microtubules. Bafilomycin A1, the vacuolar H+-ATPase inhibitor, inhibited degradation of LDL and caused accumulation of undegraded LDL within macropinosomes and multivesicular body endosomes. LDL in multivesicular body endosomes was concentrated >40-fold over its concentration in the culture medium consistent with macropinosome shrinkage by maturation into multivesicular body endosomes. Macropinocytosis of LDL taken up in the fluid phase without receptor-mediated binding of LDL is a novel endocytic pathway that generates macrophage foam cells. Macropinocytosis in macrophages and possibly other vascular cells is a new pathway to target for modulating foam cell formation in atherosclerosis.     

Electronmicroscopical observations on yolk and yolk formation in Ophryotrocha labronica LaGreca and Bacci

Summary In Ophryotrocha labronica LaGreca & Bacci mature yolk granules are found only in the ovocyte. Other typical yolk elements are lipid droplets, small vesicular bodies, multivesicular bodies and dense bodies. The two last-mentioned also appear in the accompanying nurse cell and from there obviously pass over unchanged into the ovocyte through a specific intercellular bridge, the fusome.The mature yolk granules are considered as aggregates of mitochondrial, endoplasmic and Golgi material, to which also is added pinocytotically incorporated external material. Mitochondria apparently play a fundamental role in the process, as the multivesicular bodies, most likely the direct precursors to the yolk granules, in all probability represent transformed mitochondria.Labelling with ³H-thymidine during vitellogenesis reveals presence of DNA in the yolk granules. From the labelling pattern, which shows DNA-synthesis both in the ovocyte and the nurse cell nucleus, it is concluded that the labelled material present in the cytoplasm of both cells — most of it in yolk granules and dense bodies — is of nuclear origin. The possible mitochondrial nature of yolk granule DNA is discussed.The author is indebted to Dr. Bertil Åkesson, Zoological Institute, Lund, for kindly supplying the initital material for the Ophryotrocha cultures. The excellent technical assistance of Mrs. Mariann Carleson is gratefully acknowledged. My thanks are also due to Mrs. Siv Nilsson for skilful assistance with the photography. This work has been supported by the Swedish Natural Science Research Council and Kungliga Fysiografiska Sällskapet, Lund.     

Evaluation of membrane-bound black bodies in trophozoites and cysts of Naegleria spp

Various Naegleria strains were examined to determine the possible origin and significance of membrane-bound black bodies that were found in all exponentially growing cell populations. The bodies, 40–80 nm in diameter, were distributed randomly in the cytoplasm of Naegleria with ultrastructural features typical of trophozoites. No evidence was obtained that the contents of the black bodies were synthesized in the rough endoplasmic reticulum (ER) and packaged by membranous components, which could be a primitive “Golgi complex” in these amoebae. Examination of cells in various stages of encystment indicated that at least some of the cyst wall material was synthesized and packaged by the rough ER. After condensation into amorphous granules in the cisternae, the cyst wall material appeared in vesicles of the rough ER; these were frequently seen in close proximity to the cell membrane in the vicinity of developing cyst wall. Amorphous granules (～100 nm in diameter), which had variable densities and did not appear to be membrane bound, were seen in the cytoplasm of encysting cells. The substance of these granules also seemed to be incorporated into the cyst wall. The membrane-bound black bodies appeared to be destroyed in lysosomal elements during encystment. The membrane-bound black bodies were concluded to be characteristic of trophozoites and unrelated to encytment of Naegleria.