The development of the plasma membrane reticular system in the fat body of an insect

Several insect tissues have plasma membranes that are folded inwards to make a subsurface reticulum on faces that are exposed to hemolymph. The infolds have been called plasma membrane reticular systems (RSs) to distinguish them from the somewhat similar structures found in transporting epithelia. They are characterized by having negative charges on the plasma membranes of the entranceways and by the concentration of some hemolymph proteins in their lymph spaces. Their formation and loss in the fat body has been studied by scanning electron microscopy during the fifth stadium of Calpodes ethlius (Lepidoptera, Hesperiidae). Fat body cells begin the fifth stadium arranged in ribbons with the cells linked together by a fringe of processes. In the first stage many more processes form. These partially fuse together in the second stage, leaving a subsurface reticulum connected by narrow entrances to the lateral cell faces and the face below the basal lamina. Both the cell processes and the reticular systems that they enclose are usually axially orientated. The completed RS persists for the second half of the intermoult devoted to larval syntheses when the concentration of hemolymph proteins rises. After protein sequestration prior to pupation the RS is lost and the fat body returns to being a tissue of rounded cells linked by a few enmeshed processes.     

The development of epidermal feet in preparation for metamorphosis in an insect

Insect epidermal cell surfaces can be seen by scanning electron microscopy after removal of the basal lamina. This let us study surface changes in the 5th larval stage of Calpodes ethlius (Lepidoptera, Hesperiidae) in preparation for metamorphosis at the end of the stadium, in particular changes in the basal cell processes or feet, intercellular lymph spaces, filopodia and hemidesmosomes. The feet develop in three phases, initiation, elongation and contraction. Initial growth begins immediately after ecdysis and continues until commitment to pupation 66 hr later. During this phase the feet are randomly oriented. Elongation and orientation begin after commitment to pupation. Orientation is probably achieved by selective survival and growth of those feet that are axially oriented rather than by reorientation. As the larva shortens to the pupal form late in the stadium, contraction of the feet occurs and the cells become columnar. The feet finally disappear as the cells rearrange themselves into new positions in the pupal epidermis. The lateral margins of the feet are united by adhesions even when their interdigitations are most complex. The adhesions separate an intercellular lymph space from the haemolymph. The lymph space remains small through most of the stadium, but enlarges with the loss of lateral junctions as the feet contract and eventually extends along most of the length of the columnar cells. Filopodia then form and span the gaps between the cells as though they have been induced by the separation and loss of lateral cell to cell contact. Scanning electron microscopy also shows that hemidesmosomes reflect the axial alignment of the cells even before the orientation of the feet. The hemidesmosome plaques are linear structures having a constant width of 0.15 - 0.2 mum and variable length. They arise in short sections and lengthen by the linear addition of more sections with the same width. Late in the stadium they lose their axial alignment and may become branched.     

Stage-specific effects of temperature and dietary protein on growth and survival of Manduca sexta caterpillars

The effects of temperature and dietary protein concentration on growth and survival of Manduca sexta L. (Lepidoptera: Sphingidae) caterpillars during different larval stages were examined. Sets of caterpillars were raised from hatching at one of five constant temperatures (18, 22, 26, 30 or 34°C) and on one of two artificial diets (low or high protein concentration). Mass gain, duration (development time) and mean growth rate were measured for each caterpillar for the 1st to 3rd stadia, the 4th stadium, and the 5th stadium. Temperature significantly affected mass gain during each larval stage, resulting in smaller mass gains at higher temperatures at each stage. This effect was strongest at high temperatures during the 5th stadium. Temperature significantly affected durations of each larval stage, but the effect varied among stages: for example, the duration of stadia 1–3 decreased continuously with increasing temperature, whereas the duration of the 5th stadium was shortest at 26–30°C and increased at lower and higher temperatures. The effect of temperature on mean growth rate changed dramatically across larval stages: maximal growth rate occurred at 34°C during the 1st to 3rd stadia, at 30°C during the 4th stadium and at 26°C during the 5th stadium. Higher dietary protein concentration significantly decreased the duration of stadia 1–3 and of the 4th stadium, but had no significant effect on the duration of the 5th stadium. Temperature and dietary protein had little effect on mortality rates during any larval stadium, with one exception: mortality during the 5th stadium increased dramatically at temperatures of 30 and 34°C. These results demonstrate that the effects of temperature and dietary protein concentration on growth, development and survival in M. sexta vary markedly in different larval stadia during development; 5th instar caterpillars are particularly sensitive to higher temperatures.     

Effects of ovarian maturation and insemination on the length of intermoult in Thermobia domestica

ABSTRACT. A study of the individual variability in the length of intermoult periods allows correlations to be established between reproductive and moulting cycles in adult females of Thermobia domestica (Packard) (Thysanura, Lepismatidae). By keeping the females without or with males and by changing the day of insemination, it is shown that the intermoult periods vary with the rate of ovarian maturation from the beginning of each stadium. Females with slow oocyte growth are never inseminated, even in the presence of males; they have short intermoults. Females with rapid oocyte growth can be inseminated and the timing of insemination regulates the length of the intermoults. It appears that the variability in duration of the intermoult only concerns the first part of the stadium (postecdysial period of the reproductive cycle=period of intense vitellogenesis), whereas the second part of the stadium (pre-ecdysial period=previtellogenesis) has an almost constant length. The endocrine mechanisms involved are considered, taking into account the cyclic changes in hormonal levels already described in other papers.     

Functional morphology of the lymphatic system of the rat uterus during pregnancy

In the regional lymph nodes of the uterus the comparative volume of the paracortical zone significantly increases, especially within the period of the 13th-17th days of pregnancy. In the popliteal lymph node similar effect is not discovered. From the 7th up to the 11th day edema, vasodilatation, infiltration with special leucocytes are revealed. Endothelium of the postcapillary venules is hypertrophied, contains many migrating lymphocytes, which accumulate around the vessels mentioned. The volume of the microcirculatory bed is moderately increased. By the 17th day plasmoblasts, plasmocytes, Motta's cells, monocytes and especially macrophages appear in the paracortical zone. In B-zones and in medullary sinuses blasts, plasma cells, monocytes, macrophages, mitotically deviding cells increase in number. The part of the reticular cells decreases. The tensometric method demonstrates an increasing pressure of lymph in the iliac lymph node at pregnancy. Collateralies appear in the ovarian vein system, in the broad ligament of the uterus, in the lumbar area. The uterine vascular system is supposed to participate in adaptation to pregnancy. In genesis of the regional lymph node changes, discirculatory shifts, predominating during placental organogenesis, combine with phenomena of cell migration and proliferation (clearly revealed by the time when formation of the placenta is completed).     

Stages of development of retinal photoreceptor cells in postnatal ontogenesis of the pied flycatcherFicedula hypoleuca

Electron microscopic study of the retina of the altricial pied flycatcherFicedula hypoleuca nestlings has permitted identification, in the course of development of photoreceptor cells, of several consecutive stages, each characterized by the appearance in the cell of some new stagespecific structures. At the 1st stage (the presumptive photoreceptor stage), the cell is composed of the nucleus surrounded by a small amount of the cytoplasm and two processes. The 2nd stage is characterized by formation of the inner segment in the apical cell region, while in the distal region, of the cleft (electric) contacts between the photoreceptor axon terminal and the processes of the second neurons. At the 3rd stage, a pile of membrane disks of the outer segment is formed, while in the synaptic region, the first band synapses considered as the chemical ones. At the 4th stage, a lipid droplet appears in a part of the cells, and at the 5th stage, a paraboloid. The photoreceptors of the 6th stage are young cells that continue growing but are already capable for specific functioning. Closely connected with development of the photoreceptor cells is maturation of the Müller’s glia and pigment epithelium, so that every identified stage of the photoreceptor cell development corresponds to a certain structural state of these elements. The possibility of involvement of the forming retinal cells in performance of early behavioral forms is discussed.     

A function for plasma membrane reticular systems

The basal surface in transporting epithelia is infolded in a way that encourages the formation of standing gradients. Many insect cells have a similar infolded reticular system (RS) although they are clearly not transporting epithelia. These cells are like one another metabolically in that they sequester lipid from hemolymph lipophorins (lipid transporting proteins). Dietary lipids enter the hemolymph from the midgut RS which may be an adaptation for lipophorin loading. The plasma membrane reticular system of tissues metabolizing lipids (fat body, wax glands, oenocytes, lenticles) may be an adaptation for lipophorin reception and unloading. Cationic ferritin (pI 8.5) shows all RSs are covered by a lamina functioning as a negatively charged sieve. The basal plasma membrane leading to the RS is also negatively charged. The RS is a container with charged entrances that would be expected to affect the composition of the contents. Midgut cells release lipid particles into their RS. The particles are positively charged since in tracer studies they associate with anionic but not cationic ferritin. Lipophorins are anionic. The electrostatic binding of lipid to lipophorin would make it less anionic and more likely to leave the RS when loaded, thus carrying lipid to the hemolymph. Conversely, at the destination RS, loaded lipophorin would penetrate more easily than unloaded. A change in charge with unloading would be expected to alter the equilibrium between entering and leaving lipophorin, causing protein concentration in the RS of lipid receiving tissues as has been observed in the fat body. Reticular systems may thus be reaction vessels for interactions between carrier proteins and their load.     

Physiological and endocrine changes associated with polydnavirus/venom in the parasitoid-host system Chelonus inanitus-Spodoptera littoralis

As shown earlier, parasitization by the egg-larval parasitoid C. inanitus causes in its host the precocious onset of metamorphosis in the 5th instar followed by developmental arrest in the prepupal stage. Polydnavirus/venom were shown to be responsible for the developmental arrest. We investigated how polydnavirus/venom affect growth of the host larvae and found that head capsule widths were smaller from the 4th to 6th stadium and weights were lower in the 6th stadium in polydnavirus/venom-containing larvae than in non-parasitized larvae. In an attempt to identify endocrine parameters that are modified by polydnavirus/venom and might be responsible for the developmental arrest in the prepupa, we compared juvenile hormones, juvenile hormone esterase and ecdysteroids between non-parasitized and polydnavirus/venom-containing larvae from the 4th instar until pupation or developmental arrest, respectively. Obvious differences became manifest only in the 6th instar at the pupal cell formation stage, i.e. 12 days after entry of polydnavirus/venom into the host egg. Then, prothoracic glands of polydnavirus/venom-containing larvae released less ecdysteroids and ecdysteroid titres were lower than in non-parasitized larvae; this was followed by a delayed, reduced and desynchronized increase in prepupal juvenile hormones and juvenile hormone esterase and a slightly modified metabolism of ecdysone. This indicates that polydnavirus/venom affects the endocrine system of the host only after pupal commitment and that inhibition of prothoracic gland activity is the first detectable effect.     

THE ORIGIN AND FATE OF MICROBODIES IN THE FAT BODY OF AN INSECT

The structure and life history of insect microbodies are described during the development of the fat body from the 4th to 5th larval molt through the 5th to pupal molt. The mature microbodies are flattened spheres about 1.1 x 0.9 µ, with a depression on one side where a dense mass connects the limiting membrane to the core of coiled tubules. They contain catalase and urate oxidase. The precise synchrony of development of insect cells during the molt/intermolt cycle makes it easy to study the life history of particular organelles. Phases of growth are correlated with the hormonal milieu. Mature 4th stage microbodies decrease in size before ecdysis to the 5th stage when they atrophy at the same time as the new 5th stage generation arises. The 5th stage microbodies form as diverticula of the RER and, grow while confronted by RER cisternae. The mature microbodies decrease in size when the fat body engages in massive larval syntheses. At the end of the 5th larval stage, the microbodies are invested by isolation membranes and destroyed before pupation. There are thus two mechanisms for microbody destruction: atrophy of the 4th stage organelles and isolation with autophagy at the end of the 5th stage.     

Developmental characteristics of the inferior tracheobronchial and mesenteric lymph nodes in exposure to tetracycline hydrochloride

Development of the tracheobronchial and mesenteric lymph nodes has been studied in fetuses and offsprings of Wistar rats after an intramuscular administration to the female rats therapeutic doses of tetracycline hydrochloride during the first 6 days of pregnancy (preimplantation period of embryogenesis). General histological and morphometrical methods have been applied. Under the experimental conditions certain disorders in formation of functional structures of the lymph nodes have been revealed: differentiation of the parenchyma into the cortical and medullary substance formation of follicles and their germinative centers, development of sinuses, formation of argyrophile stroma architectonics are delayed. Some distrophic and destructive changes of the reticular cells are observed, argyrophilia of the reticular fibers is more evident. Lympho- and plasmocytosis are retarded on the background of an increased eosinophilic and mast cell reaction.     

Morphogenesis of the antenna of the male silkmoth. Antheraea polyphemus, III. Development of olfactory sensilla and the properties of hair-forming cells

During adult development of the male silkmoth Antheraea polyphemus, the anlagen of olfactory sensilla arise within the first 2 days post-apolysis in the antennal epidermis (stage 1-3). Approximately on the second day, the primary dendrites as well as the axons grow out from the sensory neurons (stage 4). The trichogen cells start to grow apical processes approximately on the third day, and these hair-forming 'sprouts' reach their definite length around the ninth day (stages 5-6). Then the secretion of cuticle begins, the cuticulin layer having formed on day 10 (stage 7a). The primary dendrites are shed, the inner dendritic segments as well as the thecogen cells retract from the prospective hair bases, and the inner tormogen cells degenerate around days 10/11 (stage 7b). The hair shafts of the basiconic sensilla are completed around days 12/13 (stage 7c), and those of the trichoid sensilla around days 14/15 (stage 7d). The trichogen sprouts retract from the hairs after having finished cuticle formation, and the outer dendritic segments grow out into the hairs: in the basiconic sensilla directly through, and in the trichoid sensilla alongside, the sprouts. The trichogen sprouts contain numerous parallel-running microtubules. Besides their cytoskeletal function, these are most probably involved in the transport of membrane vesicles. During the phase of cuticle deposition, large numbers of vesicles are transported anterogradely from the cell bodies into the sprouts, where they fuse with the apical cell membrane and release their electron-dense contents (most probably cuticle precursors) to the outside. As the cuticle grows in thickness, the surface area of the sprouts is reduced by endocytosis of coated vesicles. When finally the sprouts retract from the completed hairs, the number of endocytotic vesicles is further increased and numerous membrane cisterns seem to be transported retrogradely along the microtubules to the cell bodies. Here the membrane material will most probably be used again in the formation of the sensillum lymph cavities. Thus, the trichogen cells are characterized by an intensive membrane recycling. The sensillum lymph cavities develop between days 16-20 (stage 8), mainly via apical invaginations of the trichogen cells. The imago emerges on day 21.     

Ultrastructure and ontogeny of the hair sensilla on the funicle of Calliphora erythrocephala (Insecta,Diptera)

Summary Four envelope cells are responsible for the formation of the basiconical sensilla of Calliphora. They are the thecogen, trichogen, and tormogen cells, and envelope cell 4. In early stages of development the still subepithelial sensory cilia are completely enclosed by the innermost thecogen cell. The first formation movements are initiated by a growth thrust of the hair-forming cell into the exuvial space. The sensory cilia only begin to grow into the hair anlage when the hair-forming cell has almost reached its final length. As soon as growth is completed the trichogen cell, tormogen cell, and envelope cell 4 start to excrete cuticular material. The trichogen cell forms the perforated part of the hair shaft and the stimulus-conducting system consisting of the pore tubules. The tormogen cell is responsible for the excretion of the basal non-perforated hair shaft and sheath cell 4 forms the proximal part of the socket region. The thecogen cell only begin to produce dendritic sheath material when the sensory hair is almost complete.Approximately 7–8 days after pupation the tormogen cell degenerates, having, by this time, produced about two-thirds of the sensilla cuticle. The surrounding envelope cells incorporate cell fragments of the tormogen cell. The trichogen cell continues the secretion where the tormogen cell left off. When the secretion of cuticle is finished the sheath cells begin to withdraw towards the proximal direction and to form microvilli on the apical membrane. The resulting outer receptor lymph space is bordered by envelope cell 4 and the trichogen and thecogen cells. The tormogen cell is absent in the sensilla of the imago.Abbreviations DS dendritic sheath - E4 envelope cell 4 - Ex exuvial space - G glial cell - iD inner dendritic segment - iRL inner receptor lymph space - oRL outer receptor lymph space - oD outer dendritic segment - P pore - PT pore tubules - S sensory cell - T thecogen cell - TO tormogen cell - TR trichogen cell Part 1 of a dissertation accepted by the Faculty of Bio- and Geosciences, University of Karlsruhe     

The development of porcine zona pellucida using monoclonal antibodies: II. Electron microscopy

Following our previous study on the immunohistochemistry of porcine zonae pellucidae (ZP), we undertook the present study to localize the components of the ZP with immunoelectron microscopy, using three types of anti-porcine-ZP monoclonal antibodies (Mabs), named STA-1, STA-2, and STA-3. Some organelles of the oocyte were seen to react with STA-2 and STA-3 prior to ZP formation. As soon as a follicle began to mature, STA-2 and STA-3 reacted with the perinuclear space and the endoplasmic reticular membrane of the oocyte. The follicle first reacted with STA-1 at the secondary follicle stage. At this stage, the positive reaction involved the follicular cell layer as well as the oocyte and ZP. Positive reaction was scattered within and limited to the interfollicular cell space and was never found in the cytoplasm of follicular cells. At the antral follicle stage, the oocyte was surrounded by a thick, electron-dense ZP. A strong reaction was observed in the outer layer, but no significant reaction occurred in the inner layer. The convex and ragged outer margin of the ZP was characterized by the strongest reaction.     

Sequential structural changes in the fat body of the tobacco hornworm, Manduca sexta, during the fifth larval stadium

Light and electron microscopy revealed a series of structural changes that occur in the fat body of the tobacco hornworm, Manduca sexta, during the fifth, i.e. the final, larval stadium. At each developmental stage studied, the cells of the fat body were homogeneous in structure. We found no evidence suggesting the presence of more than one type of fat body cell. Our structural data are consistent with published observations on biochemical activities of M. sexta fat body at particular developmental stages. Specific points of agreement include: (a) acquisition of Golgi complex (GC) and rough endoplasmic reticulum (RER) concomitant with the time of major protein production; (b) loss of many cellular organelles (such as GC and RER) as protein production drastically decreases; (c) accumulation of protein granules and urate granules after the onset of wandering (i.e. during the pre-pupal period); (d) accumulation of lipid and glycogen throughout the feeding period. In addition we found that (a) the plasma membrane reticular system (PMRS) developed during the period when protein secretion was great; (b) the PMRS was lost abruptly at the onset of wandering; and (c) the nucleus changed in shape from being roughly spherical to elliptoid in the pre-pupal stage. We found that the structure of M. sexta fat body is similar to that published for other Lepidoptera. However, it differs from that of Heliothis zea in that regional differences are not obviously apparent.     

Haemolymph ecdysteroid levels and cellular events in the intermoult/moult sequence of Calpodes ethlius

The haemolymph ecdysteroid titre of the last larval and pupal stadia of Calpodes ethlius was determined by radioimmunoassay. During the last larval stadium, four significant ecdysteroid peaks are present, two of which have been reported for other Lepidoptera. The first peak occurs 12 hr after ecdysis and correlates temporally with nucleolar activity, RNA synthesis and organelle formation in the fat body and epidermis. It correlates also with fat body DNA synthesis, polyploidy and the initiation of a low rate of lipid synthesis. Another peak, at 78 hr, starts its increase when the prothoracic glands no longer require the influence of the brain to produce ecdysone for pupation, and marks the first critical period. It correlates with the initiation of epidermal DNA synthesis and mitosis, and with the progressive determination of pupal characteristics (change in commitment, reprogramming). This ecdysteroid peak may also be involved in the massive intermoult syntheses in the epidermis (lamellate cuticle, wax) and the fat body (lipid, protein). The largest ecdysteroid peak is seen at 162 hr, 6 hr after the tissues no longer require the prothoracic glands for pupation (second critical period). It correlates temporally with the cessation of massive synthetic activity in both epidermis and fat body and initiates preparation for pupal synthesis in both tissues. At this time the ratio of ecdysone: 20-hydroxyecdysone is ～ 1 : 6.6.In common with other Lepidoptera, a single large ecdysteroid peak occurs during the first half of the pupal stadium. Comparisons between these events and the ecdysteroid titre are made between Calpodes and other insects.     

CALCIUM BALANCE AND MOULTING IN THE CRUSTACEA

1. Crustaceans have a high content of calcium, which is chiefly located in the skeleton as calcium carbonate. Calcium is generally the most abundant cation in the body. 2. During intermoult, the exoskeleton is usually fully calcified and the animal is in calcium equilibrium with its environment. 3. In the premoult stages calcium is resorbed from the skeleton and may be lost to the environment or stored within the body. Typically, losses are high and storage is small in aquatic species, whilst most terrestrial forms store much larger amounts of calcium and losses are reduced. Loss of calcium in soluble form by aquatic species must be by outward transport across the gills. 4. Calcium is stored in a variety of different ways, usually with a common taxonomic theme. The main forms are as calcium phosphate granules in cells of the midgut gland (Brachyura), gastroliths (Astacidea and some Brachyura), the haemocoel (some Brachyura) the posterior midgut caeca (Amphipoda) and the ventral portion of the body generally in the Isopoda. 5. At ecdysis, the skeleton is shed and the calcium remaining in it is lost from the body. 6. Recalcification begins immediately, or shortly after, ecdysis using calcium mobilized from the stores. Simultaneously, or when the stores are exhausted, other sources of calcium are utilized. These are calcium in the water (aquatic species), the food (aquatic and terrestrial species) and the exuviae (chiefly terrestrial species). 7. Marine species store little calcium and must obtain the bulk of their requirement (ca. 95%) from the water. Fresh-water species also store little calcium but have, seemingly, adapted to the lower availability of calcium by increasing the affinity of the calcium-absorbing mechanism. The rates of uptake of calcium are consequently similar in marine and fresh-water species. 8. A high degree of storage is essential for terrestrial crustaceans as they do not have access to a large aquatic reservoir of calcium. These large reserves enable the animals to reach an advanced stage of calcification, allowing the resumption of foraging and feeding necessary for completion of calcification. 9. The control of calcium metabolism during the intermoult cycle is poorly under stood. β Ecdysone appears to control the resorption of calcium and the formation of calcium stores during premoult, but the mechanism of control of calcium metabolism during postmoult and intermoult is unknown. 10. The concentration of calcium in the haemolymph of most species is high, but a large proportion of this is in non-ionized form. In premoult, total calcium levels rise as a result of calcium resorption but little change occurs in the concentration of ionized calcium. Postmoult generally sees a fall in blood calcium, sometimes below the intermoult value.     

Development of the accessory reproductive glands and genital ducts in female Schistocerca gregaria

The accessory reproductive glands of female S. gregaria are tubular extensions of the paired genital ducts, which in the mature female contain large amounts of a proteinaceous secretion used in the formation of the egg pod. In the 4th and 5th-instar female the glands are indistinguishable from the remainder of the mesodermally derived genital ducts. Towards the end of the 5th stadium, however, the accessory gland region only acquires characteristic convolutions which persist throughout the adult stages. At this time the epithelium of the entire ducts becomes reorganized into a unicellular epithelium. Only one cell type occurs throughout the length of the glands, and also in the egg calyces and lateral oviducts. The cells are inactive immediately after final ecdysis and remain in this state until the level of juvenile hormone in the haemolymph rises. The hormone acts directly on the cells triggering a rapid proliferation of organelles associated with protein secretion, and thereby increasing the volume of apical cytoplasm. Microvilli develop at the luminar plasma membrane, while irregular infoldings form at the base of the cells. As the gland matures the major organelle, the rough endoplasmic reticulum, changes from the lamellar to the vesicular form. Secretion is released into the lumen by the ‘microapocrine’ method.     

Cellular composition of various structural zones of the iliac and mesenteric lymph node of pregnant rats

The dynamic of cellular reactions demonstrates certain changes in functional activity of all structures of the node during pregnancy. A similar trend of processes in the iliac (regional for the uterus) and mesenteric lymph nodes has been defined. At early stages of pregnancy, lymph nodule are the most active, this is demonstrated as an increasing portion of lymphoblasts, macrophages and dividing cells. During this period, cell composition of the cortical plateau is relatively stable. For the paracortical zone of the mesenteric lymph nodes a rather significant decrease in the portion of middle lymphocytes and reticular cells is characteristic. There is not any significant change in the relative amount of the cells in the same functional zone of the iliac lymph nodes during the same period of pregnancy. The medullar cords demonstrate an increasing number of blast forms and young plasmocytes. However, as the pregnancy develops, the structure of the paracortical zone undergoes an essential change--progressively increases the portion of lymphoblasts and large lymphocytes. The blastic reaction in the mesenteric lymph nodes is proved to depend, to some extent, on that in the iliac lymph nodes of the same animal. Mature plasma cells become the dominating cellular element in the medullary cords. At the end of the pregnancy a relative amount of the reticular cells increases in all structural zones of the node.     

Tyrosine storage vacuoles in insect fat body

The watery vacuoles first described from larval insect fat body (Chironomus, Voinov, 1927; Aedes, Wigglesworth, 1942; Rhodnius, Wigglesworth, 1967) have been studied in 4th and 5th stage Calpodes larvae. The vacuoles arise at the beginning (E+6–24 hr) of the 4th stadium from plasma membrane infolds that separate from the cell surface as provacuoles less than 1 μm in diameter. These provacuoles grow and fuse with one another through the intermolt until about half the volume of each fat body cell is occupied by a single, large vacuole. The vacuoles begin to disappear at molting. Their membrane is either incorporated into the plasma membrane by exocytosis or fragmented into vesicles that fuse to become lamellar bodies where the membranes are presumably digested. All the vacuoles have gone by a few hours after ecdysis.The tyrosine content of the fat body increases and decreases in proportion to the size of the vacuoles. As the vacuoles decrease at molting the titre of tyrosine in the hemolymph is transiently elevated at the time when there is most demand for phenolics for cuticle stabilization. Crystals having the form of tyrosine crystallize out from vacuoles separated from the fat body. In fat body extracts separated by thin layer chromatography, similar crystals occur only in the eluates from spots corresponding to tyrosine. The vacuoles are therefore presumed to be tyrosine stores used in cuticle stabilization at molting. They correspond to a type of aqueous storage compartment that is well known in plants but hitherto little recognized in animal cells.     

Calcium,phosphorus and adenylate levels and Na(+)-K(+)-ATPase activities of prawn,Macrobrachium nipponense,during the moult cycle

Changes in calcium and phosphorus concentrations, adenylate (AMP, ADP and ATP) levels, and ratios and ATPase activities of Macrobrachium nipponense were investigated during the moult cycle. Ca level in the exoskeleton was lowest in early postmoult (stage A), increasing at stages B and through intermoult (stage C) and peaking in premoult (stage D1 and D2). The P concentrations in the exoskeleton and muscle in late premoult and early postmoult stages were higher than those at other moult stages, and were lowest in the intermoult. Muscle adenylate energy charge (AEC) changed with moult stages, and was in agreement with the change in inorganic P level in the muscle. AEC may be a direct indicator of energy metabolic activity during the moult cycle. ATP/ADP and ATP/AMP ratios in premoult and postmoult stages were higher than that in intermoult stage. Na(+)-K(+)-ATPase activities of gills, muscles and hepatopancreatic of prawns were higher in early postmoult and late premoult animals, whereas they were lower in late postmoult, intermoult and early premoult animals. Gill residual ATPase activity was significantly higher in postmoult animals, while the peak value of hepatopancreatic residual ATPase activity appeared in intermoult stage.