Article

Excretion in an oribatid mite Phthiracams sp. (Arachnida: Acari)

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Abstract

Phthiracams sp. has one pair of coxal glands. Each gland comprises a thin-walled sacculus which is specialized for the ultrafiltration of the haemolymph and a tubular labyrinth the ultrastructure of which indicates a specialization for the active resorption of material from the lumen. In addition to its digestive function, the alimentary canal of this mite is also involved in excretion. Excretory material accumulates at the haemocoelic surface of the gut wall and, after endocytosis, passes through the cytoplasm of the cells as discrete bodies which appear in the faecal pellet. The faecal pellet is covered with a peritrophic layer 250–500 nm thick which has no discernible structure and disintegrates in water.

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... Fungal hyphae (basidiomycetous hyaline hyphae or melanised hyphae of Cenococcum geophilum) were sometime present, but only in little amount and in adults only. The presence of an intestinal microflora was detected only in Rhysotritia duplicata: however, it must be noticed that bacteria were found associated with post-colon microvilli of Phthiracarus sp. by Dinsdale (1974aDinsdale ( , 1975). ...
... The last faecal pellet, located in the rectum and ready to be excreted, was always more compact and darker then the preceding one, which was still located either in the colon or in the mesenteron. Compaction of the food bolus in the colon has been described by Dinsdale (1974aDinsdale ( , 1975. Comparative observations on second-and thirdorder faecal pellets showed that plant cell wall debris were still intact in the second faecal pellet while their contours became fuzzy in the third pellet, and that the more when observing inner parts (Figs. ...
Technical Report
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This is an English translation of three papers in French which have been published in scientific journals in 1984, 1985 and 1988. The present document describes the components of a moder humus profile under Scots pine, as they can be observed under a dissecting and a light microscope. Plant litter debris, roots and animal feces were collected over a small area (5 x 5 cm) in order to be sectioned and stained. All animals and microbes (fungi, bacteria, micro-algae) collected within a small area of litter (5 x 5 cm) were identified to the finest possible taxonomic level. Gut contents were analyzed and compared with the composition of the immediate environment in order to have the most reliable view of trophic relationships between plants, animals and microbes living in the same restricted environment.
... Oribatids have been poorly studied (Tarras-Wahlberg 1960;Woodring and Cook 1962;Hoebel-Mävers 1967;Tarman 1968;Bernini 1971;Haarløv and Bresciani 1972;Woodring 1973;Dinsdale 1974Dinsdale , 1975Smrž 1989;Šustr and Hubert 1999;Bücking 2002;Alberti et al. 2003). Given their predominance in soils and plethora of species feeding on different material, much more work is needed on cryptostigmatid physiology. ...
... Posteriorly these cells, in a pseudo-stratified transitional epithelium, may represent a long-term depot against hunger in the wild, functionally working in the same way as the decapod hepatopancreas (Gibson and Barker 1979) or the hepatopancreatic portion of the scorpion alimentary canal (Awati and Tembe 1952). As Malpighian tubules are present in anactinotrichid mites, the gut in P. longicornis does not have to act as a bona fide excretory organ as in some Trombidiformes (and oribatids -Dinsdale 1975), nor as a temporary (Mitchell and Nadchatram 1969) or permanent waste dump as in mites with no anus. Whether in turn the Malpighian tubules in pergamasids have a food storage function (as fat depots-Lees 1964) remains to be confirmed. ...
Article
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A review of acarine gut physiology based on published narratives dispersed over the historical international literature is given. Then, in an experimental study of the free-living predatory soil mite Pergamasus longicornis (Berlese), quantitative micro-anatomical changes in the gut epithelium are critically assessed from a temporal series of histological sections during and after feeding on larval dipteran prey. An argued functional synthesis based upon comparative kinetics is offered for verification in other mesostigmatids. Mid- and hind-gut epithelia cell types interconvert in a rational way dependent upon the physical consequences of ingestion, absorption and egestion. The fasted transitional pseudo-stratified epithelium rapidly becomes first squamous on prey ingestion (by stretching), then columnar during digestion before confirmed partial disintegration (gut ‘lumenation’) during egestion back to a pseudo-stratified state. Exponential processes within the mid- and endodermic hind-gut exhibit ‘stiff’ dynamics. Cells expand rapidly (\(t_{1/2}=\) 22.9–49.5 min) and vacuolate quickly (\(t_{1/2}=\) 1.1 h). Cells shrink very slowly (\(t_{1/2}=\) 4.9 days) and devacuolate gently (\(t_{1/2}=\) 1.0–1.7 days). Egestive cellular degeneration has an initial \(t_{1/2}=\) 7.7 h. Digestion appears to be triggered by maximum gut expansion—estimated at 10 min post start of feeding. Synchrony with changes in gut lumen contents suggests common changes in physiological function over time for the cells as a whole tightly-coupled epithelium. Distinct in architecture as a tissue over time the various constituent cell types appear functionally the same. Functional phases are: early fluid transportation (0–1 h) and extracellular activity (10–90 min); through rising food absorption (10 min to \(>1\) day); to slow intracellular meal processing and degenerative egestive waste material production (1 to \(>12\) days) much as in ticks. The same epithelium is both absorptive and degenerative in role. The switch in predominant physiology begins 4 h after the start of feeding. Two separate pulses of clavate cells appear to be a mechanism to facilitate transport by increasing epithelial surface area in contact with the lumen. Free-floating cells may augment early extracellular lumenal digestion. Possible evidence for salivary enzyme alkaline-related extra-corporeal digestion was found. Giant mycetome-like cells were found embedded in the mid-gut wall. Anteriorly, the mid-gut behaves like a temporally expendable food processing tissue and minor long-term resistive store. Posteriorly the mid-gut behaves like a major assimilative/catabolic tissue and ‘last-out’ food depot (i.e., a ‘hepatopancreas’ function) allowing the mite to resist starvation for up to 3.5 weeks after a single meal. A ‘conveyor-belt’ wave of physiology (i.e., feeding and digestion, then egestion and excretion) sweeps posteriorly but not necessarily pygidially over time. Assimilation efficiency is estimated at 82%. The total feeding cycle time histologically from a single meal allowing for the bulk of intracellular digestion and egestive release is not 52.5 h but of the order of 6 days (\(\equiv 0.17\) total gut emptyings per day), plus typically a further 3 days for subsequent excretion to occur. Final complete gut system clearance in this cryptozooid may take much longer (\(>15\) days). A common physiology across the anactinotrichid acarines is proposed. A look to the future of this field is included.
... Could the refractive grains destined to become faeces in P. longicornis, be the finely granular yellow-brown lipofuscin pigment granules comprised of lipid-containing residues arising from lysosomal digestion (Jung et al. 2007)? Interestingly, Dinsdale (1975) in the oribatid Phthiracarus sp. (using TEM) describes excretory material accumulating at the haemocoelic surface of the gut wall, which after endocytosis, passes through the cytoplasm of the gut cells as discrete bodies which then appear in the peritrophic layered faecal pellet within the gut lumen. ...
Article
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Mid- and hind-gut lumenal changes are described in the free-living predatory soil mite Pergamasus longicornis (Berlese) from a time series of histological sections scored during and after feeding on fly larval prey. Three distinct types of tangible material are found in the lumen. Bayesian estimation of the change points in the states of the gut lumenal contents over time is made using a time-homogenous first order Markov model. Exponential processes within the gut exhibit ‘stiff’ dynamics. A lumen is present throughout the midgut from 5 min after the start of feeding as the gut rapidly expands. It peaks at about 21.5 h–1.5 days and persists post-feeding (even when the gut is contracted) up until fasting/starvation commences 10 days post start of feeding. The disappearance of the lumen commences 144 h after the start of feeding. Complete disappearance of the gut lumen may take 5–9 weeks from feeding commencing. Clear watery prey material arrives up to 10 min from the start of feeding, driving gut lumen expansion. Intracellular digestion triggered by maximum gut expansion is indicated. Detectable granular prey material appears in the lumen during the concentrative phase of coxal droplet production and, despite a noticeable collapse around 12 h, lasts in part for 52.5 h. Posterior midgut regions differ slightly from anterior regions in their main prey food dynamics being somewhat faster in processing yet being slightly delayed. Posterior regions are confirmed as Last-In-Last-Out depots, anterior regions confirmed as First-In-First-Out conveyor belt processes. Evidence for differential lability of prey fractions is found. A scheme is presented of granular imbibed prey material being first initially rapidly absorbed (\(t_{\frac{1}{2}}\) = 23 min), and also being quickly partly converted to globular material extra-corporeally/extracellularly (\(t_{\frac{1}{2}}\) = 36 min)—which then rapidly disappears (\(t_{\frac{1}{2}}\) = 1.1 h, from a peak around 4 h). This is then followed by slow intracellular digestion (\(t_{\frac{1}{2}}\) = 6.9 h) of the resultant resistant prey residue matching the slow rate of appearance of opaque pre-excretory egestive refractive grains (overall \(t_{\frac{1}{2}}\) = 4.5 days). The latter confirmed latent ‘catabolic fraction’ (along with Malpighian tubule produced guanine crystals) drives rectal vesicle expansion as ‘faeces’ during the later phases of gut emptying/contraction. Catabolic half-lives are of the order of 6.3–7.8 h. Membraneous material is only present in the lumen of the gut in starving mites. No obvious peritrophic membrane was observed. The total feeding cycle time may be slightly over 52.5 h. Full clearance in the gut system of a single meal including egestive and excretory products may take up to 3 weeks. Independent corroborative photographs are included and with posterior predictive densities confirm the physiological sequence of ingestion/digestion, egestion, excretion, defecation, together with their timings. Visually dark midguts almost certainly indicate egestive refractive grains (xanthine?) production. Nomograms to diagnose the feeding state of P. longicornis in field samples are presented and show that the timing of these four phases in the wild could be inferred by scoring 10–12 mites out of a sample of 20. Suggestions to critically confirm or refute the conclusions are included.
... Similar sub-cuticular refractive crystals have been described during feeding in Pergamasus longicornis (Berlese) by Bowman (1984) and ascribed to guanine in the Malpighian tubules. Guanine and Malpighian tubules are claimed not to exist in phthiracarids (Dinsdale 1975). ...
Article
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The occurrence of refractive crystals (aka guanine) is characterised in the Malpighian tubules of the free-living predatory parasitiform soil mite Pergamasus longicornis (Berlese) from a temporal series of histological sections during and after feeding on larval dipteran prey. The tubular system behaves as a single uniform entity during digestion. Malpighian mechanisms are not the 'concentrative' mechanism sought for the early stasis in gut size during the second later phase of prey feeding. Nor are Malpighian changes associated with the time of 'anal dabbing' during feeding. Peak gut expansion precedes peak Malpighian tubule guanine crystal occurrence in a hysteretic manner. There is no evidence of Malpighian tubule expansion by fluid alone. Crystals are not found during the slow phase of liquidised prey digestion. Malpighian tubules do not appear to be osmoregulatory. Malpighian guanine is only observed 48 h to 10 days after the commencement of feeding. Post digestion guanine crystal levels in the expanded Malpighian tubules are high-peaking as a pulse 5 days after the start of feeding (i.e. after the gut is void of food at 52.5 h). The half-life of guanine elimination from the tubules is 53 h. Evidence for a physiological input cascade is found-the effective half-life of guanine appearance in the Malpighian tubules being 7.8-16.7 h. Crystals are found present at all times in the lumen of the rectal vesicle and not anywhere else lumenally in the gut at all. No guanine was observed inside gut cells. There is no evidence for the storage in the rectal vesicle of a 'pulse' of Malpighian excretory products from a discrete 'pulse' of prey ingestion. A latent egestive common catabolic phase in the gut is inferred commencing 12.5 h after the start of feeding which may cause the rectal vesicle to expand due to the catabolism of current or previous meals. Malpighian tubules swell as the gut contracts in size over time post-prandially. There is evidence that at a gross level the contents of the rectal vesicle are mechanically voided by the physical mechanism of overall gut expansion altering the effective idiosomal volume available during prey ingestion. A complete cycle of feeding, digestion, egestion and excretion is approximately 9 days. Hunger/starvation likely commences at 10 days after the start of feeding. Up to 15 days may be needed to completely clear the idiosoma of excretory material. Nomograms for predicting the likely feeding time of mites from observations of idiosomal guanine in field samples indicate that as few as 5-6 mites scoring positive for Malpighian tubule guanine out of 20 infers a high probability that the typical time from start of feeding in a population sample was about 6 days (range 3-8 days) ago.
... Regarding consumer physiology, the mode of excretion has been shown to influence D 15 N: ureotelic (3.11‰) and uricotelic (2.73‰) organisms yielded higher enrichment than ammonotelic (2.00‰) and guanicotelic organisms (1.09‰) (Vanderklift and Ponsard, 2003). While the Arachnida, including Acari, are generally characterized as guanicotelic (Evans, 1992), there is no evidence for guanine excretion in the oribatid mite Phthiracarus (Dinsdale, 1975), and some Acari have been found to excrete uric acid (Evans, 1992), or have blind guts with no excretion at all (Mitchell, 1970). Data from other guanicotelic arachnids (spiders) show variable values for D 15 N (0.75, SD ¼ 2.68 (Oelbermann and Scheu, 2002)). ...
Article
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Although oribatid mites are essential to the decomposition of plant tissues in modern temperate forests by assisting conversion of primary productivity to soil organic matter, little is known of their paleoecologic history. Previously there has been scattered and anecdotal evidence documenting oribatid mite detritivory in Pennsylvanian plant tissues. This study evaluates the incidence of oribatid mite damage for seven major coal-ball deposits from the Illinois and Appalachian sedimentary basins, representing a 17 million year interval from the Euramerican tropics. Although this interval contains the best anatomically preserved plant tissues with oribatid mite borings in the fossil record, coeval oribatid mite body-fossils are absent. By contrast, the known body-fossil record of oribatid mites commences during the Middle Devonian, but does not reappear until the Early Jurassic, at which time mite taxa are modern in aspect. All major plant taxa occurring in Pennsylvanian coal swamps, including lycopsids, sphenopsids, ferns, seed ferns and cordaites, were consumed by oribatid mites. Virtually every type of plant tissue was used by mites, notably indurated tissues such as bark, fibrovascular bundles and especially wood, as well as softer seed megagametophytic and parenchymatic tissues within stems, roots and leaves. Significant evidence also exists for secondary consumption by mites of tissues in macroarthropod coprolites. Our data indicate that oribatid mites consumed dead, aerially-derived plant tissues at ground level, as well as root-penetrated tissues substantially within the peat. Oribatid mites were important arthropod decomposers in Pennsylvanian coal swamps of Euramerica. The wood boring functional-feeding-guild was expanded by insects into above-ground, live trees during the early Mesozoic. New food resources for insect borers resulted from penetration of live tissues such as cambium and phloem, and the invasion of heartwood and other hard tissues mediated by insect-fungus symbioses. Termites and holometabolous insects were prominent contributors to this second wave of wood-boring, exploiting gymnosperms and angiosperms as both detritivores and herbivores. An earlier emplacement of oribatid mites as detritivores of dead plant tissues continued to the present, but without a documented trace-fossil record.
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I . The histology of the mid-gut of Dactylochelifer latreilli (Leach) is described. The mid-gut is divided into two regions: an anterior diverticular region consisting of digestive cells, excretory cells, and small basal cells of unknown function, and a narrow, posterior post-diverticular region possessing a syncytial epithelium. The whole mid-gut is invested in a layer of peritoneal cells. 2. The changes in the staining reaction of protein globules undergoing intra-cellular digestion are followed. 3. The development of excretory cells is described. The function of the post-diverticular mid-gut in the excretory process is outlined. 4. Storage of fatty material and glycogen occurs in the digestive cells and in the peritoneal epithelium. 5. The structure and functions of the false scorpion mid-gut are compared with those of other Arachnids.
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The structure and formation of the peritrophic membrane (p.m.) of many in sects have been studied extensively (Wigglesworth, 1950 ; Richards, 1951 ) . Al though the need for more detailed knowledge of the fine structure of the membrane was apparent, the results of early attempts to use electron microscopy were not encouraging (Richards and Korda, 1948) . Laster, Huber and Haasser (1950) re ported some details of the p.m. of Dizippus; they found it to be a (p. 397) “¿�more or less regular network, probably fibrous, with a thin film stretched across the holes of the network.” Shortly afterwards, networks with meshes approximately 0.2 @ across and composed of fine fibrils were found electron microscopically by Lager maim, Philip and Gralén(1950) in the excreta of the clothes moth larvae (Tineola bisselliella) . These networks originated from the insect, and not from the wool which formed its food ; it was not proved that they originated from the peritrophic membrane, although this seemed likely because of the similarity between these net works and those described by Huber and Haasser. Huber (1950) reported fur ther details of the structure of the p.m. in Periplaneta orientalis, Tenebrio molitor and Bombyx mon. In all except the last the characteristic networks were found. Cross-sections of the peritrophic membrane examined in the light microscope show it to consist of several loosely adhering layers, each roughly 0.5 @ to 1
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Microfibrils in peritrophic membranes of insects — probably containing the chitin of these membranes — are arranged in only three types of texture. Sometimes these types of texture are convergent. Different stages of a given species have the same type of texture. Although in some orders the same type of texture occurs in all those species which have been investigated, there is no conformity in others. There seems to be no correlation between type of texture and either mode of formation of peritrophic membranes or nutrition of the insect.
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1. Forty-eight species of oribatids in 37 families representing most of the superfamilies were collected from various environments (littoral, salt marsh, litter, sod, and freshwater) and sectioned.2. The coxal gland is composed of a sacculus and a labyrinth in all stages of all oribatid species. Muscles, originating on the body wall, insert at several points on the thin-walled sacculus which opens into the labyrinth. The labyrinth has an internal, chitinous supporting skeleton. The type A labyrinth has 3–180° bends, producing four parallel regions, and occurs in all inferior oribatids. The type B labyrinth has 1–180° bend, producing two parallel regions, and occurs in all superior oribatids. The coxal gland duct and the lateral gland duct join, penetrate the body wall, and empty into the posterior end of the podocephalic canal. All oribatids have lateral accessory glands, but only inferior oribatids have rostral and medial glands. Three ductless coxendral bodies are always present.3. The labyrinth length in oribatids is correlated with body size and the environment of the species. Oribatids from sod, leaflitter, or moss show a simple correlation of labyrinth length (X) to total body length (Y) where Y = 4.64X. Freshwater species have a labyrinth length greater than that of comparably sized terrestrial species and salt water (littoral) species have a labyrinth length less than that of comparably sized terrestrial species. There is a greater reduction in labyrinth length in species restricted to salt marshes than in species not restricted to salt marshes.4. The probable function of oribatid coxal glands is osmoregulation. Hemolymph filtration would occur across the sacculus by positive hemolymph pressure and contraction of the sacculus muscles. Resorption of ions would occur in the labyrinth, which is noncollapsible due to the internal skeleton. The hypothesis is that in freshwater species the rate of filtration is high and resorption of ions would have to be very efficient, therefore they have an elongated labyrinth; but in salt water species water loss must be minimized and preservation of ions would be a disadvantage, therefore they have a shortened labyrinth. Excre ion may also be a function of the coxal glands. The lateral gland may possibly function as an endocrine gland involved with production of a molting hormone. The rostral glands in inferior oribatids may have a salivary function.5. The coxal glands of Peripatus, some millipedes, apterygote insects, decapod crustaceans, and all arachnid orders are homologous. The Tetrastigmata, Notostigmata, Cryptostigmata, and soft ticks have typical arachnid coxal glands. The coxal glands of higher Prostigmata may be modified into salivary, silk, or venom glands. The coxal glands in Mesostigmata, Astigmata, and hard ticks are lacking or highly modified.
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L'ilon de Blatella germanica est un important segment d'accumulation minrale. Les nombreuses concrtions d'origine ergastoplasmique, contiennent du phosphore, du chlore, du calcium, du magnesium, du potassium et du fer dans un stroma glycoprotique. La paroi de ce segment protodal est constitue d'un type cellulaire unique caractris par la prsence de feuillets apicaux et d'invaginations basales, diffrenciations membranaires dcrites dans d'autres organes de transit, mais dont la coexistence constitue l'originalit de l'ilon. La signification physiologique de ce segment digestif est discute.The ileum of Blatella germanica is an important proctodeal segment of mineral accumulation. The numerous concretions, elaborated by the ergastoplasm, contain P, Cl, Ca, Mg, K and Fe in a glycoproteic matrix. The epithelium of this segment is composed by only one type of cells which are characterized by apical leaflets and basal infoldings. These membraneous differenciations have been already described in other transit organs, but their coexistence is typical of the ileum. The physiological significance of this digestive segment is discussed.
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Bei einigen Spinnen, vor allem aus der Familie der Araneidae, bilden funktionell umgewandelte Mitteldarmzellen unmittelbar unter der Hypodermic eine nahezu geschlossene Zellschicht, die mehr oder minder stark mit Guaninkristallen angefiillt sein kann. Die distalen Zellbereiche dieser von uns als Guanocyten bezeichneten Zellen verzahnen rich mit der Hypodermis selbst oder stehen mit dem schmalen hypodermalen Hämolymphsinus in Verbindung. Thre proximalen Enden sind lang ausgezogen und schieben sich zwischen nicht umgewandelte Resorptionszellen. Jede Guanocyte steht mit dem Mitteldarmlumen in direkter Verbindung. Auf Grund des Organellenbestandes sind die Guanocyten als spezialisierte Mitteldarmzellen auzusprechen, die während der reproduktiven Periode die übrigen exkretorisch tätigen Gewebe bzw. Organe unterstützen oder ergänzen, indem sie der Hämolymphe, der Hypodermis und den benachbarten Resorptionszellen pinocytotisch purinhaltige Abbauprodukte und andere Exkrete entnehmen. Dieselben werden unter Mitwirkung eines glatten endoplasmatischen Retikulums umgebaut und temporär intrazellulär als kompliziert aufgebaute Kristalle innerhalb von membranösen Kristallsäckehen gespeichert. Die Notwendigkeit intrazellulärer Exkretspeicherung auf Grund der Ernährungs-physiologie und Abwandlungen in der Funktionsmorphologie sowie fortschreitender Alterungserscheinungen wird diskutiert.
Article
The present paper concerns the organization of the epithelium in three histologically different parts of the midgut, each possibly having a specific function in the process of digestion. Three cell types can be distinguished: The columnar or absorptive cells resemble those described in other insects, but show structural characteristics depending on their location in the epithelium. An attempt was made to determine whether there is a relationship between these characteristics and functional specializations. The occurrence of apical cytoplasmic extrusions is considered to reflect a process of degeneration. In some cases fixation artifacts may be misleading. Special attention was paid to membrane configurations believed to play a part in the formation of dense bodies. Regenerative cells also occur; their relative numbers were determined in relation to their location. A third type of cell, characterized by the presence of electron dense granules, is described.
Article
The pH within the alimentary canal of the mite ranges from 5·4 in the caecae to 6·6 in the colon and post-colon. Microchemical tests indicate the presence of protease, lipase, and carbohydrase activity in the mesenteron. The hydrolysis of carbohydrates is particularly vigorous but no cellulase activity or cellulolytic gut symbionts are apparent.A brush border epithelium lines the mesenteron but no specialized secretory or excretory regions of the gut are evident. Morphological evidence for the endocytosis of material from the lumen is confirmed with the aid of food treated by the addition of ferritin tracer, which is readily identified under the electron microscope. Lysosomes are identified in the wall of the mesenteron using the histochemical localization of acid phosphatase and cholinesterase activity within membrane-bounded organelles. The existence of an intracellular mechanism for digestion is postulated, which could account for the hydrolysis of protein and, possibly, small particles of cellulose, but polysaccharides are probably broken down at the brush-border and in the gut lumen.The cells of the gut wall may also ingest material from the haemocoel, as indicated by the purely morphological evidence of invaginations in the external wall of the gut. It is suggested that this process may involve the intracellular digestive system of the gut wall in a ‘retinculoedothelial’ mechanism.
Article
An electron microscope study was made of the development of the peritrophic membrane (PM) of the mosquito, Aedes aegypti. Thin sections were stained with heavy metals, some of which were unusual, and both normal and extracted membranes were examined.The PM is secreted in a blind pouch formed by protrusion of the oesophagus into the anterior end of the midgut. The cuticle of the oesophagus tapers in thickness and at the end of the oesophagus consists of only epicuticle. There is no intergradation to midgut. At one particular cell boundary cuticle ceases, microvilli appear, and the appearance of the cytoplasm changes.The PM is formed from material secreted by a ring of midgut cells in the anterior half of the proventricular pouch. Cross-sections show about 40 cells; longitudinal sections show that the PM material comes from the anteriormost 8 to 10 of these cells; therefore, some 300 to 400 cells are involved. The PM is already present in larvae when they hatch from the egg. It becomes thicker and with more microfibrous layers as the larvae grow.The fully formed PM in an older larva is a differentiated structure consisting of a granular-appearing layer about 0·25 μm thick underlain by usually three layers of crossed microfibres separated by low density regions with very faint irregular fibres. The total thickness is about 1 μm. Extraction studies show that all of these parts contain chitin-protein units, and that accordingly chitin occurs in the PM in both fibrous and non-fibrous form.Reasons are detailed for concluding that the ring of midgut cells secrete a material that is or contains a chitin-protein component, that this material is of unknown physical state (viscous fluid?) but appears granular in stained thin sections, and that as this material moves posteriorly some physico-chemical phenomenon induces post-secretion aggregation to produce layers of microfibres within this secretion. The nature of the fibre-inducing and fibre-orienting mechanisms remains unknown but does not seem to involve a direct control by the secreting cells or their microvilli.The PM is not comparable in ulstrastructure to the cuticle of the larva. There is no equivalent of an epicuticle. Particles of a few dozen nanometers diameter do not penetrate into the PM from either side. The PM is affected by digestive enzymes and some other chemicals, and begins to show degradation in the more posterior parts of the gut.In contrast to existing literature, there is no evidence for the existence of a ‘mould’ or a ‘press’ and extrusion mechanism. There are a pair of cuticular collars at the end of the oesophageal valve but these do not form any mould or press—perhaps they restrict food from getting back into the proventricular pouch where the PM material is secreted, or aid in propelling the PM posteriorly. It is suggested that the only difference between the so-called type I and II of the PM's is the restriction of secretion to a ring of cells at the anterior end of the midgut in type II.There is no PM in the pupal stage, in the adult male, or in the unfed young adult female. However, within a short time after taking a blood meal a membrane, which we must call a PM, appears around the food bolus. The PM of the adult female is different from that of the larva: it is induced by feeding, it is thin, it shows no internal differentiation. This species, then, is an exception to Peters' generality that different stages of any one species have similar PM's.
Article
The midgut epithelial cells of Fulgora candelaria are covered by a unique plexiform surface coat, 2–4 μ thick. It has two layers. The outer layer consists of saccules of membranes, each saccule containing a membranous vesicle from which radiates a “fuzz” of filaments and granules. The inner layer is formed from flattened sacs of membrane. The coat is cytochemically defined as a PASpositive acid mucopolysaccharide. The membranes of the coat have a striking similarity in dimensions and morphology to the plasma membrane of the underlying microvilli of the midgut epithelial cells.
Article
Guanophores in the back skin of the adult tree frog have been studied with an electron microscope. The cytoplasm is characterized by numerous needle- or platelet-like clear spaces which are incompletely surrounded by their own limiting membranes. These clear spaces are arranged in many groups and run in parallel with each other within the group. However, in extremely thick unstained sections, the cytoplasm is filled up with many dense inclusions, guanine crystals, instead of spaces. It is suggested, therefore, that the clear spaces are empty cavities and represent almost the sites of guanine crystals which were removed away from ultrathin sections probably by mechanical pressure applied during cutting. Except for ordinary cell organelles, fine filaments about 60 Å in bundles are scattered in the cytoplasm.
Variations de I'ultrastructure des tubes de Malpighi et leur fonctionnement chez Gryllus domesticus. C.r. hebd Recherches sur les Glandes coxales et la regulation du milieu interne chez I'Ornithodorus moubata
  • A Berkaloff
Berkaloff, A. (1959). Variations de I'ultrastructure des tubes de Malpighi et leur fonctionnement chez Gryllus domesticus. C.r. hebd. Skanc. Acad. Sci., Paris 248: 466469. Bone, G. J. (1943). Recherches sur les Glandes coxales et la regulation du milieu interne chez I'Ornithodorus moubata. Annls SOC. r. zool. Belg. 74: 16-31.
Les grains de sécrétion des tubes de Malpighi de Gryllus domestkus
  • Berkaloff A.
Berkaloff, A. (1958). Les grains de skrktion des tubes de Malpighi de Gryllus domesticus. C.r. hebd. SPanc. Acad. Sci., Paris 246: 2807-2809.
Recherches sur les Glandes coxales et la regulation du milieu interne chez l'Ornithodorus moubata
  • Bone G. J.
Light and electronmicroscopical studies on the alimentary system of an oribatid mite Nothrus palustris (C. L. Koch 1840)
  • Haarløv N.
Recherches sur l'ultrastructure et l'histochimie de l'organe coxal d'Ornithodorus moubata (Murray) (Ixodoiden Argasidae)
  • Hecker H.
Electronmicroscopic studies of the guanine storage cells of Araneus diadematus (Clerck)
  • Seitz
Struktur und Bildungageschwindigkeit peritrophoscher Membranen von Calliphora erythrocephala
  • Zimmerman U.