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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.

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.

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 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.

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)

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.

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.

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.

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.