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The male gametes of the gnathostomulid bursovaginoid Austrognathia sp. were investigated by electron microscopy. All stages of sperm development can be observed in the single saccular male gonad, which is enclosed by a relatively thick basement membrane internally reinforced by thin smooth muscle cells. The spermatogonia are situated close to the testicular theca and produce generally separate primary spermatocytes. From secondary spermatocytes onwards, the nuclear envelope is no longer visible. The spermatids develop synchronously in groups of four, in contrast to arthropod and vertebrate spermatogenesis. A single, large nurse cell, or trophocyte, never observed previously, surrounds each spermatid; perhaps it represents an altered germ cell functioning in nutrition. The spermatid nucleus, initially ovoid, lengthens and takes on the shape of a mushroom head extending into a stalk. Three degrees of chromatin condensation are visible. Anteriorly, a palisade-shaped structure is present just over the highly heterochromatic nuclear zone and is considered to have an acrosome-like function. The outer sperm cytoplasm is characterized by a peripheral tubular labyrinth. Axonemal structures have never been found, but centriole-like structures are present among the medium-density chromatinic strands of the mushroom-like nucleus. No cortical microtubules are evident beneath the cell membrane. The external sperm morphology recalls that of nematode gametes, and some internal features are also similar. Phylogenetic considerations and hypotheses on sperm locomotion are proposed. J. Morphol. 237:165-176, 1998. © 1998 Wiley-Liss, Inc.

A new species, Philosyrtis aegusae sp. nov., collected in the ‘Otoplanen-Zone’ of the sands of western Sicily, is described. The specimens show the typical morphological peculiarities of the subfamily Parotoplaninae (‘Turbellaria’: Otoplanidae), but differ clearly from the species already described. The body length of the sexually mature animals reaches 0.9–1.1 mm and they appear to belong to the genus Philosyrtis because of the general arrangement of testes and germo-vitellaria, and of the sclerotic apparatus. The vesicula granulorum is clearly distinct from the sclerotic apparatus unlike the other ten species belonging to the same genus. The male copulatory organ consists of a dorsal group of 7–8 spines similar in shape and length (33–40 mm), and a ventral group of at least 6 long thin spines with curved pointed tips. The new species differs from the already described species above all in its body dimensions, the shorter path of the vitellaries and especially the characteristics of the male sclerotic apparatus.

A new species, Postbursoplana parafibulata sp. nov., is described from lower interstitial habitats of the Upper Tuscan sea coast (Ligurian Sea). The specimens display the typical collar-shaped pharynx, perpendicularly positioned, of the subfamily Parotoplaninae (“Turbellaria”, Otoplanidae). The sexually mature animals are 1.2–1.4 mm in length, and appear to belong to the genus Postbursoplana because of the general arrangement of testes and germo-vitellaria, and of the sclerotic apparatus characteristics. Their male copulatory organ consists of 10 spines differentiated in five groups with variable shape and length (52–73 μm). P. parafibulata sp. nov. differs from the already described species above all for the body dimensions and the characteristics of the sclerotic male apparatus. The new species appears more similar to P. fibulata collected in the Mediterranean Sea.

Parotoplana rosignana sp. nov., collected at Marina di Cecina, Rosignano Solvay, Castiglioncello and Quercianella (Leghorn, Ligurian Sea), shows a body length of 0.8–1.6 mm. Behind the brain on both sides, two longitudinal rows of medium–large testes reach, in a single line, two germaries at about one‐third of body length. Immediately after the small ovaries two rows of vitellaries are present on both sides; these run along the ‘kragenformig’ pharynx to the penis papilla opening. The male copulatory organ has 12 spines of variable shape and length (79–125 µm) and a central funnel‐shaped sting (80 µm long). The first description of the post‐embryonal development of otoplanids is given in this flatworm, and it appears of proterogynic type, but the maturation of the female and male gametes in the adult is contemporaneous.

A new species, Otoplana oxyspina, sp. nov., collected in the “Otoplanen‐Zone” of the Ligurian Sea, is described. Although the specimens show the typical morphologic peculiarities of the subfamily Otoplaninae (“Turbellaria”, Proseriata), they nevertheless differ clearly from the species already described. The body length reaches 3.3–4 mm and the anterior end is characterized by the presence of a swelling between the two couples of thick retractile tactile bristles. The rhabdites are grouped into longitudinal rows along the body with the exception of the anterior end. The vitellaries, present on both sides from the anterior end to the pharynx opening, consist of two longitudinal rows. Internally, two longitudinal rows of testes reach the paired germaries located in front of the pharynx. The male copulatory organ consists of a pointed median aculeus (56 µm long) and 20 spines of different shape and length (36–65 µm). This new species differs from O. intermedia and O. truncaspina in its body dimensions, the s...

Our immunocytochemical investigation positively identified for the first time at the ultrastructural level the presence of GABA‐ir neurones and terminals in the nervous system of a plathelminth, the acoel Symsagittifera psammophila. The gold particles are localized on clear vesicles (about 30–60 nm wide) of somata and terminals prevalently distributed in the neuropile area near the statocyst. GABA‐ir vesicles are also present at neuromuscular junctions. The significance of this finding in a lower invertebrate is discussed.

The brain of Strongylostoma simplex shows the organization typical of the most evolutionary groups of free-living plathelminths. Three types of neurons, two types of neurosecretory cells, and a certain number of glia-like cells are present. Somato-axonic synapses and axo-dendritic contacts with a “spine apparatus”, like those described in vertebrates, have been identified. These two types of synapses have never been reported in other plathelminth brains. Local thickenings and dense bars attached to the presynaptic membrane are also observed, together with the paramembranous density common in many flatworm synapses.

The eye of a typhloplanid flatworm was investigated by electron microscopy. It consists of a silvery unicellular optic cup similar to a cockscomb flower and of three photoreceptors. The cup is made up of a cell containing reflecting crystalline platelets, arranged in parallel rows inside four laminae. Each photoreceptor is provided with a rhabdomeric photoreceptoral process, some lateral cytoplasmic projections, and an axon. The microvillar border faces medially and makes contact with a reflecting lamina. This eye could discriminate light direction.

The spermatogenesis of Allostoma sp. and the organization of mature spermatozoa are described by means of transmission electron microscopy. All stages of sperm development were observed in mature testes, which are bordered by a layer of fibrous connective tissue. The primary spermatogonium produces 64 spermatids, grouped as a cytophore. The process of spermiogenesis occurs at the periphery of the cytophore, when the sperm body is formed and released at complete maturation. The mature spermatozoon is a flattened, filiform structure. It is aciliary. Its anterior end is not distinguishable from the posterior one in the testis. The nucleus, showing an approximately rectangular cross section, is situated centrally and the chromatin is densely packed. A membranous cylinder, located on each side of the nucleus, contains conspicuous stacks of clear thick-envelope vesicles, and a long mitochondrial derivative placed peripherally. The vesicles show contacts with the cylinder membrane and the outer sperm membrane. Their supposed Golgi-derived content may thus be released into the external medium. A hypothesis is proposed about the role of these vesicles in sperm motility.

Grey mullet peripheral blood lymphocytes could be ultrastructurally separated into small cells (‘resting cells’), T and B cells and plasma cells. Such cells were morphologically distinguishable independently of cell-surface antigenic markers.

The protonephridial system of Gotte's larva of Stylochus mediterraneus was studied by electron microscopy. There is one protonephridium on each side of the body, formed by one terminal and one canal cell. The terminal filtration apparatus is formed by a single cell (the terminal cell) with several globular processes, the largest of which includes the nucleus. Fingers of cytoplasm (leptotriches) from each process penetrate the lumen surrounding the bundle of cilia and fingers from adjacent processes interdigitate to form a pattern of convoluted slits which constitute the weir. The single canal cell is inserted internally to the terminal cell at the top of the weir and encloses the lumen without a junction. Septate junctions are present between the terminal and canal cells. The lumen of the canal cell is smooth-walled for most of its length and cilia arise and terminate at all levels of the terminal and canal cells. Posterior to the larval mouth opening, the canal cell crosses the epithelium and the lumen ramifies to form the excretory opening. The terminal apparatus closely resembles that found in the freshwater planarian Bdellocephala brunnea.

The fine structure of the nerve cells and the neuropile in the brain of acoels and the peripheral nervous system and the synapses have been studied. On the basis of the vesicle content, four nerve cell types are distinguished. The presumptive glial cell is also visualized. The synapses appear to be of the following four types: asymmetrical, ribbon, symmetrical and electrical. The peripheral nervous system consists of a subepithelial and a submuscular plexus; they present asymmetrical and symmetrical synapses. In the light of these results, the nervous system of acoels should no longer be considered as primitive.

Diabetes acutely impairs the ability of the liver to synthesize glycogen. However, the effect of chronic diabetes on the glycogenic function of the liver is not known. We measured hepatic glycogen contents in streptozotocin (STZ)-diabetic rats 3 weeks or 9 months after the induction of diabetes, in the fed state and following a 24-hour fast. In the fed state, liver glycogen levels were markedly decreased in short-term diabetic animals (5.8 +/- 2.0 v 33.9 +/- 2.3 mg/g, P less than .001), but not in long-term diabetic rats (18.3 +/- 4.4 v 20.7 +/- 1.3 mg/g, P = NS) as compared with age-matched nondiabetic animals, despite comparable hyperglycemia (portal plasma glucose levels of 424 +/- 21 and 449 +/- 24 mg/100 mL, short- and long-term diabetics, respectively). In the fasted state, on the other hand, liver glycogen was depleted in acute diabetes (4.5 +/- 2.2 mg/g v 1.9 +/- 0.5 of control rats), but significantly increased in chronic diabetes (10.1 +/- 3.1 v 0.2 +/- 0.03 mg/g, P less than .001). The latter finding was confirmed by electron-microscopical examination of liver cells. Furthermore, the percentage of hepatic glycogen synthase in the active form (synthase a) was lower than normal in short-term diabetic rats and in old nondiabetic rats. In long-term diabetic animals, on the other hand, synthase a was significantly higher than in old controls (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Each pigment-cup eye of Mesostoma ehrenbergi consists of two photoreceptor cells, the anterior cell being bilobate. the posterior almost linear, and of a multicellular pigment cup. The nuclei of the photoreceptor cells are located inside the medial region of the brain. Thin cytoplasmic photoreceptor projections provided with neurosecretory-like granules are interposed between the inner surface of the eye cup and the distal extremity of the microvilli. The breakdown and renewal of microvillar membranes was analysed. Membrane turnover is a continuous process. At dusk and during the night abscission of photoreceptive membranes occurs. At dawn the membrane fragments are degraded to granular material, which is then endocytosed into the submicrovillar cytoplasm as coated vesicles. These vesicles form multivesicular bodies. The degradation of multivesicular body content occurs during the following light hours. The dark period is correlated with membrane synthesis for elongation of reticular membranes, which are converted into ellipsoid bodies. The formation of new microvillar membranes occurs at the base of the microvillar border, and involves the fusion with the old microvillar membranes of small vesicles detached from the tubular endoplasmic membranes and from the flattened concentric cisternae of ellipsoid bodies. The correlations with daily cycles of other invertebrates are discussed.

The fine structure of Keilin's sense organ of Ceratitis capitata (Wiedemann) larva (Diptera : Tephritidae) was studied. It is considered to be a trichoid mechanoreceptor, as is apparent from the morphology of the distal dendritic segment provided with a tubular body, and from the presence of an ecdysial pore or scar at the base of the hair shaft. None of the distinct structural elements. such as the socket rim, socket septum and suspension fibres, which are usually associated with trichoid mechanoreceptors, are present. The tormogen cell has not been found. Furthermore, the lack of any permeable pore also speaks in favour of a mechanosensitive function, as is the case of the majority of aporous sensilla.

Background/Aims: The effects of acute insulin deficiency on the kidney have been investigated in animal models of experimental diabetes; however, the impact of long-term diabetes has not been determined. Methods: We measured renal glycogen contents in streptozotocin (STZ)-diabetic rats 3 weeks (n = 12) or 9 months (n = 12) after the induction of diabetes, and in 2 groups of control rats of similar age (n = 16 and n = 12, respectively), in the fed state and after a 24-hour fast. Results: Diabetic rats had high glucose levels, low insulin but normal glucagon concentrations in portal blood. In the fasting state, kidney glycogen content was very low in both young control and young diabetic rats (54 ± 15 and 189 ± 26 µg/g, respectively, mean ± SD); in contrast, glycogen levels were markedly elevated in rats with long-standing diabetes as compared to old nondiabetic animals (2,628 ± 1,023 ± and 1,968 ± 989 µg/g of diabetic rat, fasting and fed, respectively, p < 0.001 vs. 0 ± 0 and 4 ± 6 µg/g of control rats). On electron microscopy, large glycogen clusters were localized to the renal tubules. Kidney phosphorylase activity was higher, and synthase activity lower in diabetic than control rats (p < 0.05 for both), whereas kidney glycogen was strongly related to plasma glucose levels, suggesting that the enzyme changes were secondary to glycogen accumulation itself. Renal hexosephosphates and fructose-2,6-bisphosphate contents were both increased in long-term diabetic rats (p < 0.05), implying enhanced fluxes through both glycolysis and gluconeogenesis. Conclusion: In chronic, untreated diabetes glycogen accumulates in the renal tubules; prolonged hyperglycemia is the sole driving force for this phenomenon.

Summary To improve knowledge of the processes involved in fruit abscission, the abscisic acid levels and the structure of both whole seed and single seed tissues were investigated in control (sample A) and shedding affected fruits (sample B) of Malus domestica . ABA content was measured in crude extracts by radioimmunoassay and the results were validated by physicochemical methods. Whole seeds were embedded and sectioned for light and electron microscopy studies. The ABA level in whole seeds was almost three times higher in the affected fruits than in the control. No difference in ABA content was observed between the embryos of the two samples, while in the endosperm, the nucellus and especially in the integuments, the ABA level was clearly higher in sample B than in sample A. Delayed development and precocious cell differentiation as well as certain aspects of whole system degeneration were observed. The authors conclude that ABA levels seem to be one of the factors involved in fruit abscission in an early period of development.

The four eyes of the prolecithophoran Allostoma sp. are disposed in two pairs in a dorsolateral position at the periphery of the brain and beneath its capsule. They are rhabdomeric pigment-cup ocelli. Each eye in the anterior pair consists of one pigment cell and one receptor cell; each in the posterior pair is made up of a larger, single pigment cell and two photoreceptor cells. A lens in front of the pigment cell’s aperture is formed by electron-dense, refractive, finger-like protrusions which arise from unpigmented cytoplasmic extensions of the pigment-cup margin. Degenerative signs are sometimes visible in the lens.

The epidermal eyespots of the acoel Otocelis rubropunctata would appear to consist of a single cell type provided with pigment granules and cilia. Very numerous dictyosomes characterize the cytoplasm of the cells. The cilia possess the 9X2 + 2 pattern of microtubules and the typical rootlets of acoels. Microvilli are interspersed among the cilia. The basal surface of the cells seems to present synatpic input and to generate an axonal process, which would confirm their photosensitive role. The structural similarities with other photoreceptors are outlined.

Each pigment-cup eye of Polycystis naegelii consists of two retinal clubs and a single pigmented cell. The latter is divided into two cavities by a septum. Under bright illumination the photoreceptor process appears as a disk containing membranous laminar whorls; under faint illumination the latter are replaced by numerous straight, closely packed, microvilli. This morphological variation is correlated with the intensity of the photoreceptor's exposure to light. The lenticular structures described by previous light microscopists have not been observed.

Two new species of Otoplanidae belonging to the subfamily Parotoplaninae are described: Parotoplana macrostyla sp.n. and P. uncinate sp.n. In both species the anterior body end bears a swelling. The rhabdites are grouped into bundles of several elements (up to 20 or more). The caudal plate is fan-shaped. The cuticular apparatus has a stylet and two types of spines. The germovitelloducts do not form the common duct and the bursa stalk has a peculiar structural pattern.

The otoplanid nervous system investigated in Otoplana truncaspina Lanfranchi, 1969 and Parotoplanella heterorhabditica Lanfranchi, 1969 consits of: (a) an ellipsoidal cerebral ganglion located between the gut and the cephalic intestine and invested by a fibrillar collagen-like capsule 0.3 μm thick; (b) anterior extracapsular ganglion cell clusters; (c) a peripheral nerve plexus locally thickened at the level of the epithelial sensory and glandular areas, with extensive synaptic connections. At least two neuron types can be identified within the ganglion: (a) an inner layer close to the central neuropile of the 1st type of neurons, showing a vesicular cytoplasm rich in RER and Golgi complexes processing both round, clear, 25–45 nm in diameter, and dense cored vesicles, 50–80 nm in diameter; (b) an outer layer of the 2nd type of neurons, adjoining the capsule and filled with uniformly dense vesicles, 60–90 nm in diameter. Synaptic endings in the neuropile are provided with clear vesicles and dense cored vesicles or uniformly dense vesicles. The presynaptic side has paramembranous projections channelling the vesicles to the active zone; omega-like profiles are also observed. Thin banded muscle fibres run within the brain. A comparison is drawn with the other turbellarian neuron types described in the literature, to suggest their possible function. The functional implications of the synaptic ultrastructure are discussed.

The statocyst architecture in the three otoplanid species Notocaryoturbella bigermaria Lanfranchi, 1969, Otoplana truncaspina Lanfranchi, 1969 and Parotoplanella heterorhabditica Lanfranchi, 1969 is compared. Common features are: (a) a fibrillar collagen-like, 0.2 μm thick, investing capsule continuous with the brain capsule; (b) an inner wall made up of six or more flattened and overlapping parietal cells; (c) a statolith forming cell hanging from the dorsal side down in the lumen, with a large statolith containing vacuole; (d) a bilateral pair of spindle shaped accessory cell groups, adjoining the statolith cell and sending projections to the wall—nerve projections run through the capsule; (e) one accessory cell enveloping the other cells of the group has a filament containing cytoplasm, the filaments coverging into a hemidesmosome making contact with a projection coming from a parietal cell; (f) muscles from the longitudinal body musculature inserting onto the capsule externally. The lack of ciliary structures differentiates the turbellarian statocyst from the majority of invertebrate statocysts. The developmental origin, the phylogenetical meaning and the functional and adaptive value of the statocyst in Turbellaria are here commented on.

In Notocaryoturbella bigermaria, Otoplana truncaspina and Paroto-planella heterorhabditica three types of epidermal receptors are recognized. Type I: with a single cilium running in a duct, piercing the distal dendrite process of the receptor. The internal wall of the dendrite process has eight ridges with longitudinal filaments lying inside them. The ciliary basal body lacks a longitudinal rootlet but is encircled by a thin annular formation. Type II: with a single (A) or several (B) cilia which protrude from the outer epithelial surface and are provided with a large and striped rootlet. Both types are considered as mechanoreceptors. Type III: with two or more short and stumpy cilia devoid of rootlets and displaying the usual 9 + 2 pattern in the proximal part only. They are considered as chemoreceptors.

The circadian light—dark cycles in the dalyelliid flatworm eyes induce two changes of particular interest. One involves the metabolic membrane system, its turnover, and the localization and appearance of mitochondria and glycogen; the other is connected with retinomotor response. In the second process the dark-adapted eye presents an empty eye cup. The microvillar border of the photoreceptors and the “lens” projections come out of the cup and the cell bodies are displaced laterally with respect to that cup. An attempt was made to elucidate the development within time of the retinomotor response. The plot of the ratio of empty area/microvillar area in median sections of several eyes shows a long-lasting dark-adaptation, completed in 6–9 hr and a short-term light-adaptation completed 5–10 min after light onset. Some hypotheses on the regulation of this response are discussed.

The appearance and development of the embryonic and larval eyes of the polyclad turbellarian Stylochus mediterraneus were studied. In the embryo, the left epidermal eye appears first. Subsequently, the right epidermal eye appears, and within hours it sinks into the parenchyma and turns into a cerebral eye. Newly hatched Gotte’s larvae possess both the left epidermal and the right cerebral eye. Three days after hatching, an incomplete eye appears adjacent to the left epidermal eye. The left cerebral eye then originates from this incomplete eye as it sinks into the parenchyma. This third eye is believed to originate through a process of induction.

Morphological development of photoreceptor outer segments and synapses in the foveal region of the pigeon retina was studied by electron microscopy. In addition, the maturation of outer retina function was investigated by recording electroretinographic (ERG) responses to either flash or pattern stimuli. The first ERGs to unpatterned or patterned stimulation can be recorded at 4–6 days posthatching. These results are consistent with anatomical analysis of pigeon photoreceptor and synapse development. Indeed, photosensitive lamellae in the outer segments can be observed simultaneously with the appearance of the first retinal responses to light. A few synapses can already be seen in the outer plexiform layer at the time photoreceptor disks first appear. In contrast, numerous synapses are already present in the inner plexiform layer when photoreceptor lamellae have yet to appear. A comparable maturation pattern has been reported to occur in chicks toward the end of the incubation time.

Examination of the larvae of Thysanozoon brocchii and Stylochus mediterraneus shows that they have both epidermal and cerebral eyes, while the young worms of Notoplana alcinoi have only cerebral eyes. A description is given of the ultrastructure of both kinds of eyes. The epidermal eye consists of one cup-shaped pigmented cell, whose cavity is filled with lamellae of ciliary origin. A small covering cell is located over the cup-opening. The cerebral eye is made up of three cells: one pigmented cell with ciliary projections and two rhabdomeric-type photoreceptor cells. The cerebral eye in the adult is formed of a pigmented cup without cilia and at least three rhabdomeric-type photoreceptors. A number of remarks of a morpho-onthological nature are presented.