Vesicular Connective Tissue Cells Research Articles

Effects of temperature and salinity on the sub-Antarctic snail Xymenopsis muriciformis (King and Broderip, 1832): Medium-term exposure to different climate change scenarios

As a consequence of climate change, benthic marine species that inhabit the sub-Antarctic oceans could be impacted as a result of changes in temperature and salinity that are affecting areas of high latitudes, where stenoic marine species are common. Therefore, the physiological performance of the species is essential to understand the ability of species to persist within their current range and to predict their rates of redistribution in response to the impacts of climate change impact. Xymenopsis muriciformis, an endemic sub-Antarctic benthic snail of the Strait of Magellan (53° 47′S; 70° 58′W), was used as a model species to understand the physiological response of a species that inhabits the Southern Oceans, where environmental conditions are very stable. We tested a medium-term exposure to the effects of climate change, including changes in temperature and salinity. The organisms were acclimatized for three months in the laboratory, at a temperature of 9 °C and salinity of 30 psu (control). The experiment was carried out for 60 days, where the ingestion rate and oxygen uptake were measured every 10 days. At the end of the experiments, the physiological condition of the organisms was determined by applying the metabolic indicators: carbohydrate indices (CHI), total lipids (TLI) and lipofuscins (LI), which were obtained by histological-histochemical analysis. The results indicated that temperature had significant effects on the ingestion rate and oxygen consumption, while salinity and the interaction between salinity and temperature had no significant effects. Organisms exposed to low temperatures (1 °C) and (5 °C), expected for the southern hemisphere summer, exhibited cellular degradation, which would limit the access and colonization of Antarctic environments. The organisms exposed to the 15 °C treatment (expected for the Magellan region), presented a significantly higher amount of lipofuscins in the vesicular connective tissue cells with morphological characteristics in the autophagosomes. We concluded that the snail X. muriciformis is a characteristic stenoic species, highly sensitive to temperature variations, as those projected in climate change scenarios for the Antarctic and sub-Antarctic regions.

Autophagy in nutrient storage cells of the Pacific oyster, Crassostrea gigas

In oysters, nutrients are stored in a special type of cells referred to as vesicular-connective tissue cells (VCT-cells). These cells accumulate and provide nutrient to satisfy various needs of the organism, including gametogenesis. During the annual reproductive cycle, VCT-cells pass through a series of changes in their morphology associated with nutrients mobilization for developing germ cells. The results presented here show an approximately 33–35% increase in the number of autophagic vesicles in cytoplasm of VCT-cells in the gonadal area of C. gigas during the stage of active gametogenesis as compared to the resting stage of reproductive cycle. No destruction of VCT-cells due to autophagy or any other factors was observed, both in males and females. Our results indicate that autophagy does increase in VCT-cells of C. gigas and plays a certain role in nutrient mobilization from these cells.

The Mussel Mytilus galloprovincialis in the Bay of Naples: New Insights on Oogenic Cycle and Its Hormonal Control.

The aim of the present article was to investigate the oogenic cycle of Mytilus galloprovincialis sampled in the Bay of Naples, and to immunolocalize 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD), and P450 aromatase, enzymes involved in the synthesis of two sex hormones: testosterone and 17β-estradiol. We demonstrate that the oogenic cycle starts in late summer-early fall and continues in early winter when the first event of spawning occurs; other spawning events take place until June, when the ovary is spent and contains a few empty ovarian follicles and numerous somatic cells, that is, adipogranular cells and vesicular connective tissue cells. During the oogenic cycle, apoptotic events occur at the level of oogonia, previtellogenic oocytes, as well as follicle cells; by contrast, necrosis events probably take place in vitellogenic oocytes, which, once degenerated, transfer their content to healthy oocytes. Finally, the present data demonstrate that 3β-HSD, 17β-HSD, and P450 aromatase are present in the ovary both during the reproductive and nonreproductive phases. The possible role of these enzymes during the Mytilus galloprovincialis reproductive cycle is discussed. Anat Rec, 302:1039-1049, 2019. © 2019 Wiley Periodicals, Inc.

Ultrastructure of oocytes during oogenesis and oocyte degeneration associated with follicle cells in female sinonovacula constricta (BIVALVIA: PHARIDAE) in western Korea

The ultrastructure of oocytes during oogenesis and oocyte degeneration associated with follicle cells in female Sinonovacula constricta (Lamarck, 1818) were investigated by electron microscope observations. Ovarian follicles are surrounded by a matrix of vesicular connective tissue cells (VCT cells). VCT cells contain large quantities of glycogen particles and several lipid droplets in their cytoplasm. It is suggested that VCT cells act as a source of nutrients for vitellogenesis during oogenesis. In early vitellogenic oocytes, several coated vesicles, which appear at the basal region of the oocyte, lead to the formation of membrane‐bound vesicles via endocytosis. The uptake of nutritive materials in coated vesicles formed by endocytosis appears through the formation of coated pits on the oolemma during vitellogenesis. During the late stage of oogenesis, yolk precursors (yolk granules), mitochondria and lipid droplets are present in the cytoplasm of late vitellogenic oocytes. In particular, proteinaceous yolk granules containing several different components are intermingles and form immature yolk granules. In the mature oocyte, small immature yolk granules are intermingled and form large mature yolk granules. Vitellogenesis occurs through a process of autosynthesis, involving combined activity of the Golgi complex, mitochondria and rough endoplasmic reticulum in the cytoplasm of vitellogenic oocytes. The process of heterosynthesis is where extraovarian precursors are incorporated into oocytes by endocytosis at the basal region of early vitellogenic oocytes before the formation of the vitelline coat. Follicle cells appear to play an important role in vitellogenesis and oocyte degeneration. The functions of attached follicle cells to the oocyte during oocyte degeneration are phagocytosis and digestion of phagosomes originating from oocyte degeneration. After digestion of phagosomes, it is assumed that the function of follicle cells can permit a transfer of yolk precursors necessary for vitellogenesis and allows for the accumulation of glycogen and lipid during oocyte degeneration, which can be employed by vitellogenic oocytes. Follicle cells of S. constricta may possess a lysosomal system for induction of oocyte breakdown and might resorb phagosomes in the cytoplasm for nutrient accumulation during oocyte degeneration.

Histochemical and ultrastructural characterisation of mantle storage cells in the hydrothermal-vent bivalve Bathymodiolus azoricus

This study reports on two types of storage cells that are present in the mantle connective tissue of the deep-sea mussel Bathymodiolus azoricus. One type corresponds to the adipogranular cells, a kind of storage cell previously described in other bivalves. In these cells extensive regions of the cytoplasm are filled with glycogen deposits and these zones became strongly stained after histochemical (PAS) or ultrastructural detection of polysaccharides. Several lipid droplets and membrane bound granules containing homogeneous electron-dense material are also present in adipogranular cells. A second type of cell contains large lysosomes in addition to numerous lipid droplets, but lacking cytoplasmic glycogen deposits. Due to these characteristics we named them adipolysosomal cells. They can be identified in semi-thin sections stained with PAS reaction because the lysosomes are the only positively stained structures. In the connective tissue of the mantle, some cells containing many lysosomes and a few lipid droplets were also observed. These cells differ from the adipolysosomal cells mainly because they have a reduced amount of lipid reserves, and could be an initial stage in the development of adipolysosomal cells. The vesicular connective tissue cells that in other Mytilidae are specialised in glycogen storage were not detected in B. azoricus. The reserves accumulated in the two types of storage cells described in B. azoricus may be important for the survival of these hydrothermal-vent bivalves if their nutrition is affected by a temporary loss or reduction of endosymbiotic bacteria due to sulphide and/or methane shortage caused by oscillations in vent activity.

Occurrence of the Pathogen Haplosporidium nelsoni in Oysters, Crassostrea virginica, in South Carolina, U.S.A.

The presence of the pathogenic protozoan Haplosporidium nelsoni is documented for the first time in the American oyster, Crassostrea virginica, from South Carolina, U.S.A. Initially incriminated in 1957 as the causative agent of mass mortalities in the American oyster, Crassostrea virginica, in Delaware Bay, Haplosporidium nelsoni was given the acronym MSX (multinucleated sphere X) because its systematic relationship to other organisms was unknown. Subsequently, it was designated as Minchinia nelsoni by Haskin et al. (1966). Still later, Sprague (1979) transferred the species to the genus Haplosporidium (Balanosporida: Haplosporidiidae). The devastating effects of H. nelsoni on C. virginica are well known (see reviews by Lauckner, 1983; Sindermann, 1990; Sparks, 1985). It, along with Perkinsus marinus, another protistan parasite, are undoubtedly the major causes of the decline of the oyster industry in both the Delaware and Chesapeake Bays. Although H. nelsoni has been known by a few investigators to parasitize C. virginica in South Carolina, its occurrence in this state has never been recorded (Burrell, 1986). MATERIALS AND METHODS During November and December 1991 and January 1992, we examined 35 young oysters, 5-6 cm long, collected intertidally in Charleston Harbor (salinity 15-17%oo at Fort Johnson. The soft tissues of these bivalves appeared watery, with recessed mantles, and in each one of the six clusters studied, at least one or two were dead. These were native, wild oysters, the ancestors of which had inhabited Charleston Harbor for at least 100 years. No drought had occurred for at least three years prior to the time of collection. Moreover, no mass mortalities of oysters had been reported at the time. 1 This research was supported by a grant (NA16FL0408-01) from the National Marine Fisheries Service, U.S. Department of Commerce. TRANS. AM. MICROSC. Soc., 112(1): 75-77. 1993. ? Copyright, 1993, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.224 on Wed, 14 Dec 2016 05:02:50 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC. All of the living oysters were removed from their shells and processed for histopathologic examination. All were fixed in 10% seawater formalin, embedded in paraffin, sectioned at 7 ,im, and stained with hematoxylin and eosin for light microscopy. RESULTS AND DISCUSSION Intercellular plasmodia of Haplosporidium nelsoni were found in each oyster. All of the observed plasmodia were in relatively early stages of karyokinesis in that none was observed to include more than 10 nuclei. A few dividing nuclei, with conspicuous spindle fibers, also were observed (Farley, 1967). The plasmodia observed measured 6-10 ,um in greatest diameter. Although the majority of the plasmodia occurred between Leydig cells (i.e., vesicular connective tissue cells) situated between acini of the digestive diverticula and in the matrices of gill filaments, some also were found in various hemolymph sinuses and vessels as well as suprabranchial chambers, thus indicating systematic infections (Kanaley & Ford, 1990). In addition to plasmodia, spores, each measuring 6-8 Aim in length, were observed. These were located between Leydig cells in the hosts' digestive diverticula. H. nelsoni spores are seen rarely and to date have been reported only by Couch et al. (1966) and Barrow & Taylor (1966). The fact that we observed spores in the oysters examined during November through January in South Carolina is of interest because in the Chesapeake and Delaware Bays, sporulation of H. nelsoni usually occurs in June and July (Couch et al., 1966). Our finding of spores during the stated collection period may reflect the warmer temperatures that prevail during autumn and winter in South Carolina coastal waters. Haplosporidium nelsoni has been reported along the Atlantic coast of the United States from Massachusetts, Connecticut, New York, New Jersey, Delaware, Maryland, Virginia, North Carolina, and the Atlantic Coast of Florida (Haskin & Andrews, 1988). Recently, H. nelsoni was reported in C. virginica from coastal Georgia (Lewis et al., 1992). Our observations document the first record of the occurrence of H. nelsoni in South Carolina.

Isolation, characterization and glucose metabolism of glycogen cells (=vesicular connective-tissue cells) from the labial palps of the marine mussel Mytilus edulis

A method has been developed to isolate glycogen cells (=vesicular connective tissue cells) from the labial palps of the marine mussel Mytilus edulis L. These cells have a modal density of 1.14 g ml-1 and this property has been exploited to separate them from pronase-dissociated cell dispersions by density-gradient centrifugation. The isolated cells were mainly spherical, with a small peripheral nucleus. The quasitotality of the cell was filled with β-like glycogen particles with cellular organelles being limited to the cell periphery. The major recipients of [U-14C] glucose-derived carbon were glycogen and amino acids. Only small quantities of 14C radiolabel were recovered from lipids, protein and CO2. Glucose incorporation into glycogen increased linearly over 6 h and showed saturation kinetics with respect to exogenous glucose concentration.

Ultrastructural and cytochemical study on interactions between nutrient storage cells and gametogenesis in the mussel Mytilus edulis

The ultrastructural morphology of storage-cell breakdown and replenishment in Mytilus edulis is described for mussels collected at monthly intervals over a period of one year (September 1981 to October 1982) from a site in Cornwall, England. In addition cytochemical staining reactions at light and electron microscope levels are described for the storage cells and the Sertoli cells. The breakdown of adipogranular (ADG) cell components is believed to be a lysosomally-mediated process of controlled autolysis involving fusion of primary lysosomes with the protein granules. Increasing activity for lysosomal enzymes during ADG cell breakdown is demonstrated using quantitative cytochemistry. The presence of glycogen in vesicular connective tissue (VCT) cells is demonstrated using freeze-dried, formaldehyde-vapour-fixed tissue. The breakdown of VCT cells involves sequestration of glycogen from the central reserve into small cytoplasmic vesicles; subsequent release appears to be mediated by eccrine secretion. The presence of arylsulphatase activity in lysosomes within the peripheral cytoplasm of the VCT cells during the winter months indicates that glycogen breakdown may also be lysosomally mediated. The morphology of the Sertoli cells is described; during the early stages of spermatogenesis they are characterized by the presence of numerous lipid droplets which are depleted as development proceeds. Contact between Sertoli cells and developing spermatogonia is maintained by means of long septate junctions. Following spawning, the well developed lysosomal system is evident in the Sertoli cells and appears to be engaged in intracellular digestion of phagocytosed waste sperm and residual cytoplasm. Resorption of the products of gamete degeneration by the gonoduct epithelial cells is described. During regeneration, VCT cells appear to endocytose material; the ADG cells demonstrate extensive arrays of rough endoplasmic reticulum and are occasionally seen undergoing mitosis. A process involving loss of glycogen vesicles from the mantle epithelial cells by means of apocrine sections is described.

The Influence of Starvation and of Increased Carbohydrate Intake On the Polysaccharide Content of Various Body Parts of the Pond Snail Lymnaea Stagnalis

In the present study the haemolymph-glucose concentration, the tissue wet weights and the amount of polysaccharides in the various body parts of the pond snail Lymnaea stagnalis were determined after feeding lettuce ad libitum, and after various periods of starvation or of feeding on a carbohydrate rich diet (Bemax). During starvation the haemolymph-glucose concentration remained rather constant, at the same level as in lettuce fed snails (about 15 µg/ml). Feeding Bemax caused a significant increase in the glucose concentration (3-4 fold). Tissue wet weights decreased significantly during starvation (by about 40%) but did not change in snails fed Bemax. The total amount of polysaccharides of all body parts together was about 25 mg in lettuce fed snails. During 15 days of starvation this value decreased till about 9 mg (-65%), whereas after feeding Bemax during the same period this value increased till about 51 mg (+ 100%). This suggests that the metabolism ofL. stagnalis is carbohydrate orientated. Of the various body parts the mantle, the digestive gland/ovotestis and the muscle fraction are very important both in the mobilization (83% of the total amount lost) and in the storage of polysaccharides (84% of the total amount stored). The storage function of the mantle and also of the digestive gland/ovotestis is mainly due to the glycogen storing properties of the vesicular connective tissue cells (VCTC). In the muscle fraction, the muscle cells will be important in the storage. The other body parts (female accessory sex organs, prostate gland and rest fraction) are of little importance in the mobilization and the storage of polysaccharides. It is noted that the polysaccharide content of the female organs is not indicative for their synthetic activity, as at the end of the experiment the synthesis of galactogen will be doubled in Bemax fed snails, due to the doubled amount of eggs produced. It is suggested that the increase in the haemolymph-glucose of Bemax fed snails stimulated the synthesis of polysaccharides (glycogen and galactogen). After saturation of the main storage centres (VCTC and muscle cells) an equilibrium is reached between the influx of dietary glucose and the loss of polysaccharides via the female reproductive system. The stimulation of the polysaccharide synthesis may be either directly or via hormone producing organs.

Effects of Different Kinds of Food, Starvation and Restart of Feeding On the Haemolymph-Glucose of the Pond Snail Lymnaea Stagnalis

In the present study, the amount of glucose and of some other carbohydrate components in the haemolymph of laboratory bred specimens of Lymnaea stagnalis was studied in relation to different feeding conditions. The snails, normally fed on lettuce, were fed on a carbohydrate rich diet (Bemax), were starved, or were fed again after a period of starvation. It is demonstrated that the haemolymph-glucose concentration has a rather constant level of 16μg/ml in lettuce fed snails. This level, however, can be slightly different for snails originating from various breeding tanks. During starvation (up to 15 days) the haemolymph-glucose remains at the same constant level as in lettuce fed snails. Reproduction and growth stop and especially the former will cause a reduced need for glucose. Some glucose, however, is needed for metabolism. It is suggested that the haemolymph-glucose is maintained at a constant level during adverse conditions (such as starvation) at the expense of, mainly, polysaccharides present in the vesicular connective tissue cells and in the reproductive organs. When feeding again on lettuce after a period of starvation and when feeding on a carbohydrate rich diet (Bemax), within 1 day the haemolymph-glucose level is raised (to 36 μg/ml and 144 μg/ml, respectively) above the level of lettuce fed control snails. This raise in the glucose concentration in the haemolymph is only temporary in the animals fed again on lettuce. After 7 days of feeding the glucose level is no longer significantly different from the value of lettuce fed control snails. Also reproduction and growth are resumed after this period. It is suggested that a raise in the glucose concentration in the haemolymph (caused by the restart of feeding) is a stimulus for the start of reproduction and growth. The raise in the glucose concentration in the haemolymph of snails fed on Bemax, lasts during the whole experimental period (7 days). At the end of this period the haemolymph has a raised, constant glucose concentration of 86 μg/ml which represents an equilibrium between the increased glucose influx in the haemolymph and an increased use of glucose by glucose consuming processes like storage and reproduction.

Host-Parasite Interrelationships Between the Freshwater Pulmonate Biomphalaria Pfeifferi and the Trematode Schistosoma Mansoni

The influence of infection with S. mansoni on reproduction, growth, food consumption and survival in B. pfeifferi was studied experimentally (Ch. II). The prepatent period in infected snails was shown to last 22-24 days under the conditions prevailing in the relevant experiment. The number of eggs laid by infected snails as compared with controls was significantly reduced from 7-10 days postinfection onwards. After day 13 postinfection it was completely suppressed in the majority of the infected snails. The increase in shell diameter in infected specimens was larger than that of the controls between 7 and 18 days, that in weight between 11 and 21 days postinfection. Gigantism did not occur. There was no difference in mortality between infected and control snails prior to the 11th week after the beginning of the experiment. After that, the mortality among infected specimens showed a sharp rise. Uninfected and infected snails consumed similar amounts of food (dried lettuce) in the first two weeks of the experiment. After that, infected snails consumed less food than controls. The digestive gland of B. pfeifferi was studied with histological, histochemical and ultrastructural methods (Ch. III). The highly folded epithelium of the ducts connecting the digestive gland with the pyloric part of the stomach, consists of cilia and/or microvilli bearing columnar cells with interspersed mucous cells. In the epithelium of the digestive gland two main cell types are distinguished: the digestive cell and the secretory cell. In addition some mucous cells occur. It is concluded that the main functions of the digestive cell are absorption and endocytosis of predigested food material, followed by intracellular digestion. Indigestible residues are accumulated in a large vacuole, which eventually is excreted. The secretory cell produces and secretes proteinaceous substances, presumably digestive enzymes. It does not store calcium. The so-called excretory cells, which are in fact degenerating secretory cells, have vacuoles containing yellow globules. These yellow globules together with cell debris are finally released into the lumen of the digestive gland. The observations indicate that the digestive gland is not important as a storage organ for reserve material. The lobules of the digestive gland are covered by a thin connective tissue sheath, consisting of ground substance, collagen-like fibrils, smooth muscle cells and cells with the appearance of pigment cells. The connective tissue between the lobules of the digestive gland and the acini of the ovotestis, and between these organs and the mantle, consists mainly of vesicular connective tissue cells. These cells are supposed to play an important metabolic role as storage cells for glycogen. The tegument of the daughter sporocyst of S. mansoni (Ch. IV), consisting of an outer syncytial anucleate layer which is joined by cytoplasmic connections to nucleated cell bodies (tegumental cells), has the same basic architecture as that described for various stages of trematodes and cestodes. Well-developed mitochondria, GER cisternae and tubules, free ribosomes and polysomes, and lipid droplets occur throughout the tegument. The ultrastructural features suggest that the outer layer is involved in uptake of nutrients by absorption and endocytosis. The poorly developed musculature is loosely arranged in two layers beneath the outer tegumental layer. The nucleated portions of the muscle fibres are situated between the tegumental cells. The protonephridial system consists of flame cells with efferent tubules. The bundle of cilia, implanted in the flame cell, beats in the cilia chamber or barrel. The proximal part of the barrel consists of alternating rib-like extensions of the flame cell and of the first tubule cell, respectively. Ultrafiltration probably takes place in the ribbed part of the barrel. The development of cercariae from germinal cells is briefly described. The pathological effects of infection with S. mansoni on the digestive gland epithelium of B. pfeifferi (Ch. V) are limited. From about 12 weeks after infection slight changes occur, but they are difficult to distinguish from changes due to ageing of the cells. The effect of starvation on the digestive gland epithelium is much more marked than the adverse influence of infection. Compression of digestive gland lumina by daughter sporocysts was not observed. Changes in the connective tissue of the digestive gland due to the presence of daughter sporocysts were: development of muscle cells into cells with the appearance of pigment cells and/or degeneration of these muscle cells, and an increase in the number of amoebocytes, which become involved in the elimination of cell debris and in the formation of a loose layer over the parasites.

Sarcoma-like disease in a single specimen of the American oyster.

AbstractAn unusual lesion observed in the right mantle of an oyster, Crassostrea virginica [see Couch: Nat. Cancer Inst. Monogr. 31: 557–562, 1969], resembles certain reticulum sarcomas of mammals. Characteristics shared by the oyster tumor and mammalian reticulosarcoma are: (1) relatively large blastoid (anaplastic?) cells with scant cytoplasm and enlarged, pleomorphic nuclei; (2) occasional binucleate or multinucleate cells; (3) many mitoses (many more than found in comparable normal or injured tissue); (4) focal (tumor-like condition) rather than diffuse distribution of blastoid cells; and (5) altered patterns of reticulum fibers.Further histological and cytological study of this tumor, utilizing Lillie’s stain for reticulum and the mercury bromophenol blue method of Mazia, Brewer and Alfert for total protein, reveals that alterations in the connective tissue stroma result from invasion and replacement of normal vesicular connective tissue cells by large blastoid cells. These stromatic alterations are of two forms: (1) collapse and aggregation of remnants of normal reticulum fibers upon replacement or degeneration of normal vesicular cells; and (2) apparent (though, perhaps, not real) increase in reticulum in limited areas of the tumor as compared to normal areas in other oysters. The blastoid cells have a marked affinity for the total protein stain in cytoplasm and nuclei and show a much more intense staining for protein than do normal hemocytes, vesicular cells, and epithelial cells.Additionally, abundant mitotic activity suggests that active protein synthesis is a biochemical characteristic of oyster blastoid cells and supports the hypothesis that these are largely undifferentiated or anaplastic, neoplastic cells. It is recognized that active protein biosynthesis is a characteristic of normal cells undergoing division or elaborating secretory substances. However, the intensely proteinaceous nature of these cells is related to their neoplastic character since this oyster tumor and its unusual blastoid cells are highly abnormal and rare (1/5,000 oysters examined). The Alcian blue method for acid mucopolysaccharides showed no increase in acid mucopolysaccharides in the tumorous mantle epithelium, or in the lesion proper. No recognizable parasites or infectious agents were found in the oyster sections studied.The origin of the blastoid cell remains enigmatic. Additional specimens with this rare conditions are essential for further study.

Structure and Physiology of the Organs of Feeding and Digestion inOstrea edulis

The anatomy and histology of the food collecting and alimentary organs of the adult oyster are described.The anatomy of the stomach is investigated with the aid of gelatin casts and attention drawn to the food caecum, the ventral groove, and the two ducts of the digestive diverticula.Cilia and mucus glands are universal throughout the food collecting and alimentary organs.There is evidence that the gastric shield is composed of fused cilia.The histology of the style-sac resembles that described by Mackintosh for Crepidula. There is evidence that secretion of the style takes place in the groove.Phagocytes are everywhere numerous in the blood vessels, connective tissue and epithelia, and free in the gut and mantle cavity.The alimentary organs of the larva are described.The anatomy and histology of these organs in the spat isdescribed, the palps are relatively large and the gills asymmetrical. The style-sac is distinct from the mid-gut.The course of the ciliary currents on the gills and palps is described and the importance of the various selective mechanisms emphasized.Selection appears to be purely quantitative, large particles or mucus masses being rejected and smaller ones accepted.Muscular activity is of great importance in the functioning of both gills and palps. Reversal of cilia has never been seen.Rejected matter is removed from the mantle cavity.Material is sorted in the food caecum in the stomach, larger particles passing into the mid-gut and smaller ones towards the gastric shield and ducts of the digestive diverticula, within the tubules of which there is a constant circulation.The rotation of the style assists in the stirring of matter in the stomach.In the style-sac are cilia, which rotate the style and others which push it into the storuach.In the larva the velum acts as a food collecting organ ; the style lies in an extension of the stomach and rotates rapidly. Material passes freely into the digestive diverticula.In the spat rejective mechanisms are highly developed. The style revolves at a speed of between sixty and seventy revolutions per minute.The tubules of the digestive diverticula are the only place where soluble matter is absorbed, in adult, larvae, or spat.Fine particles are ingested and digested intracellularly in the tubules of the digestive diverticula, the products of digestion carried away by amoebocytes, and useless matter rejected into the lumen.Larger particles are ingested and digested by phagocytes in all parts, the products of digestion being carried to the vesicular connective tissue cells and there stored.Enzymes in the style digest starch and glycogen. The amylase, at pH 5.9, has an optimum temperature of 43'C, and is destroyed atThe optimum medium is pH 5-9. It is inactivated by purification with absolute alcohol or by dialysis, but action is restored on the addition of chlorides or bromides and to a less extent iodides, nitrates, and carbonates, but not with sulphates or fluorides.Sucroclastic enzymes in the digestive diverticula act on starch, glycogen, sucrose, raffinose, maltose, lactose, salicin, and amygdalin, but not on inulin, cellulose, or pentosans.The amylase, at pH 5-5, has an optimum temperature of 44-5, and is destroyed at between 64 and 67. It has an optimum pH of 5-5, and is inactivated after purification or dialysis, action being restored in the presence of chlorides or bromides.There is a weak lipase and protease, the latter has two optima at pH 3-7 and at or above 9-0 ; its action is very slow.The only enzymes free in the stomach are those from the style.There is no evidence of any enzymes free in the gill mucus.There is a powerful complete oxidase system in the style, and a catalase in the digestive diverticula and gonad, and traces in the palps, gills, and muscle.The style is the most acid substance in the gut and the cause of the acidity of the gut.The style is dissolved rapidly in fluid of pH 2-3 and above, but very slowly below that point. It is readily dissolved and reformed in the oyster, its presence depending on the maintenance of the balance between the rate of secretion and the rate of dissolution. Its condition is a valuable indication of the state of metabolism.Glycogen and fat are stored, particularly in the vesicular connective tissue cells, the former furnishing the principal reserve food material.The presence of abundant supplies of microscopic plant life rich in carbohydrates provides ideal food for the oyster, and represents optimum conditions for fattening and reproduction.