Twin Cones Research Articles

Hydrothermal fluid circulation within the restless structural frame of Hasandağ volcanic system (Central Anatolia, Türkiye) inferred from Self-potential, CO2, and temperature measurements

Hasandağ is an active composite volcanic system located in the Central Anatolian Volcanic Province (CAVP). A comprehensive field survey was conducted to reveal the hydrothermal activity within the Hasandağ volcanic system, with particular emphasis on Self-Potential (SP) mapping. The Hasandağ system is characterised by the presence of twin stratovolcanoes that arise from pre-existing partially buried calderas. In conjunction with the SP measurements, carbon dioxide concentration (CO2) and surface temperature (ST) measurements were taken. The temperature measurements were elaborated with thermal infrared remote (TIR) sensing methods. The SP results, with a peak-to-peak magnitude of 3.8 Volts, revealed the presence of a significant hydrothermal input in both of the twin cones, characterised by a typical W-shaped anomaly commonly observed in active volcanoes. The highest SP signal coincides with the active fumarole zone at the western flank of G. Hasandağ summit, where we measured ∼70 °C vapour temperatures and relatively high CO2 output (>100,000 ppm). The SP/elevation (Ce) gradient assisted in revealing the hydrothermal and hydrogeological zonation, providing substantial evidence of the relationship between hydrothermal circulation and the structural frame of the volcano. Integrated evaluation of SP, CO2, and temperature data revealed the structural control on the hydrothermal and hydrogeological circulation, with the contribution of Hasandağ, Karacaören, and Karkın Faults as major structural components. The partially buried rim of the Hasandağ caldera was revealed through the detection of a ‘double Ce-low’ signal, providing valuable insights on the dimensions of the structure and its role in the hydrogeological cycle of the system. The extent and magnitude of the hydrothermal activity observed, the Holocene eruptive history of the volcano, and its proximity to populated areas denote the requirement of further geophysical and geochronological research and the necessity of hazard assessment and instrumental monitoring.

The eye of the tongue sole Cynoglossus bilineatus (Lacepède, 1802) (Teleostei: Pleuronectiformes)

We report the ocular features of the tongue sole, Cynoglossus bilineatus (Lacepède, 1802), a marine, bottom-dwelling flatfish. In this species, both eyes are located juxtaposed on the same side of the flat head. Histology revealed the sclera to be fibrous (collagenous) in nature. The choroid possesses the choriocapillaris, and adjacent to it, 3–4 rows of iridophores with stacks of cytoplasmic platelets. No choroidal gland is present. The retinal pigment epithelium (RPE) contains scanty melanin granules. Its vitread half is modified into a dense tapetum with lipid spheres (about 0.34 μm in diameter). In juveniles, the tapetal spheres arise by budding from the smooth endoplasmic reticulum of the RPE. There are blood vessels within the retina; the vitreal vessels penetrate the retina and ramify close to the level of the outer limiting membrane. The vessels are capillaries in nature. The photoreceptor layer contains abundant rods, and twin cones and single cones, being arranged into square mosaics. The optic disc is non-pleated and shows pan- cytokeratin immunopositivity, which is related to the bundled cytokeratin filaments detected in astrocytes by electron microscopy. The retinal tapetum and choroidal iridophores help the species to live in a muddy bottom having dim-light environment. The lack of a choroidal gland, hypoxic aquatic condition and presence of a dense retinal tapetum (that limits O2 transport to the photoreceptors) appear to have favored the proliferation of vitreal vessels within the retina in this species. The fibrous sclera has probably arisen to provide structural support to the eye in migration from the lateral to the dorsal aspect of the head during larval metamorphosis.

Retinal adaptations of southern bluefin tuna larvae: Implications for culture

We examined Southern bluefin tuna, Thunnus maccoyii, larvae to identify specific retinal adaptations that would indicate both important parameters for culture and larval ecology in the wild. Plastic resin histology, microspectrophotometry and behavioural feeding responses were used to describe visual development. Thunnus maccoyii larvae reflected the visual morphogenesis template commonly observed in many other marine fish species exhibiting indirect development. First-feeding (3 days post-hatching, [dph], 3.4 mm standard length [SL]) larvae possessed tightly packed single cone photoreceptors. Rods and twin cones were present in the retina in post-flexion larvae (21 dph, 8.39 mm fork length [FL]) with cone mosaic patterns observed in juveniles (30 dph, 21 mm FL). Based on the spacing of adjacent photoreceptors and focal length, first feeding larvae had a maximum theoretical visual acuity of 1.23 ± 0.11° that decreased to 0.14 ± 0.02° at 30 dph. Thunnus maccoyii displayed high cell density in the ventral retinal region (cones, bipolar and horizontal cells), a low convergence of cone cells to ganglion cells throughout the retina during larval development (1.1 ± 0.2 to 1.4 ± 0.3 at 3 dph and 30 dph, respectively), and early development of retinal pigment epithelium (RPE) migration. Microspectrophotometry showed twin cone visual pigments maximally sensitive to light in the blue-green part of the visual spectrum (wavelength of maximum absorption [λmax] of 494 nm, 507 nm and 524 nm), and behavioural experiments showed they fed preferentially at these wavelengths. Increased retinal cone densities in the ventral region indicated a localized region specialized for acute vision for prey and predator detection in the upward direction (dorsal plane) at an early age, representing a possible adaptation to life in deeper oceanic waters. The apparent high acuity and photopic sensitivity observed in T. maccoyii is hypothesised to be associated with the ability to feed in low light conditions. This has important practical considerations in determining lighting regimes for culture of T. maccoyii and possibly for other tuna species.

Seeing red: color vision in the largemouth bass.

How animals visually perceive the environment is key to understanding important ecological behaviors, such as predation, foraging, and mating. This study focuses on the visual system properties and visual perception of color in the largemouth bass Micropterus salmoides. This study (1) documents the number and spectral sensitivity of photoreceptors, (2) uses these parameters to model visual perception, and (3) tests the model of color perception using a behavioral assay. Bass possess single cone cells maximally sensitive at 535 nm, twin cone cells maximally sensitive at 614 nm, and rod cells maximally sensitive at 528 nm. A simple model of visual perception predicted that bass should not be able to discern between chartreuse yellow and white nor between green and blue. In contrast, bass should be able to discern red from all achromatic (i.e., gray scale) stimuli. These predictions were partially upheld in behavioral trials. In behavioral trials, bass were first trained to recognize a target color to receive a food reward, and then tested on their ability to differentiate between their target color and a color similar in brightness. Bass trained to red and green could easily discern their training color from all other colors for target colors that were similar in brightness (white and black, respectively). This study shows that bass possess dichromatic vision and do use chromatic (i.e., color) cues in making visual-based decisions.

Mud Volcanism in a Canyon: Morphodynamic Evolution of the Active Venere Mud Volcano and Its Interplay With Squillace Canyon, Central Mediterranean

AbstractSubmarine mud volcanoes develop through the extrusion of methane‐rich fluids and sediments onto the seafloor. The morphology of a mud volcano can record its extrusive history and processes of erosion and deformation affecting it. The study of offshore mud volcano dynamics is limited because only few have been mapped at resolutions that reveal their detailed surface structures. More importantly, rates and volumes of extruded sediment and methane are poorly constrained. The 100 m high twin cones of Venere mud volcano are situated at ∼1,600 m water depth within Squillace Canyon along the Ionian Calabrian margin, Mediterranean Sea. Seafloor bathymetry and backscatter data obtained by a ship‐based system and an autonomous underwater vehicle (AUV) allow mapping of mudflow deposits of the mud volcano and bedforms in the surrounding canyon. Repeated surveying by AUV document active mud movement at the western summit in between 2014 and 2016. Through sediment coring and tephrochronology, ages of buried mudflow deposits are determined based on the sedimentation rate and the thickness of overlying hemipelagic sediments. An average extrusion rate of 27,000 m3/yr over the last ∼882 years is estimated. These results support a three‐stage evolutionary model of Venere mud volcano since ∼4,000 years ago. It includes the onset of quiescence at the eastern cone (after ∼2,200 years ago), erosive events in Squillace Canyon (prior to ∼882 years ago), and mudflows from the eastern cone (since ∼882 years). This study reveals new interactions between a mud volcano and a canyon in the deep sea.

Anatomical Analysis of the Retinal Specializations to a Crypto-Benthic, Micro-Predatory Lifestyle in the Mediterranean Triplefin Blenny Tripterygion delaisi.

The environment and lifestyle of a species are known to exert selective pressure on the visual system, often demonstrating a tight link between visual morphology and ecology. Many studies have predicted the visual requirements of a species by examining the anatomical features of the eye. However, among the vast number of studies on visual specializations in aquatic animals, only a few have focused on small benthic fishes that occupy a heterogeneous and spatially complex visual environment. This study investigates the general retinal anatomy including the topography of both the photoreceptor and ganglion cell populations and estimates the spatial resolving power (SRP) of the eye of the Mediterranean triplefin Tripterygion delaisi. Retinal wholemounts were prepared to systematically and quantitatively analyze photoreceptor and retinal ganglion cell (RGC) densities using design-based stereology. To further examine the retinal structure, we also used magnetic resonance imaging (MRI) and histological examination of retinal cross sections. Observations of the triplefin’s eyes revealed them to be highly mobile, allowing them to view the surroundings without body movements. A rostral aphakic gap and the elliptical shape of the eye extend its visual field rostrally and allow for a rostro-caudal accommodatory axis, enabling this species to focus on prey at close range. Single and twin cones dominate the retina and are consistently arranged in one of two regular patterns, which may enhance motion detection and color vision. The retina features a prominent, dorso-temporal, convexiclivate fovea with an average density of 104,400 double and 30,800 single cones per mm2, and 81,000 RGCs per mm2. Based on photoreceptor spacing, SRP was calculated to be between 6.7 and 9.0 cycles per degree. Location and resolving power of the fovea would benefit the detection and identification of small prey in the lower frontal region of the visual field.

Morphological characteristics of visual cells in the endemic Korean loach Kichulchoia multifasciata (Pisces; Cobitidae) by microscopy.

The visual cell of the retina in the Korean loach Kichulchoia multifasciata, a bottom-dwelling freshwater loach in shallow water, contains double cones and large rods. With light microscopy, the cones form a row mosaic pattern in which the partners of double cones are linearly oriented with a large rod. In a double cone or twin cone, the two members are unequal such that one cone may be longer than the other. An anatomical unit is apparent which consists of 5 rod cells and 15 double cone cells per 20 × 20 μm area. We found that the cone cells of outer segments are linked to the inner segment by so-called "calyceal process" using a scanning electron microscopy, unlike rod cells. In the transmission electron microscopy, the outer membrane shows piles of membrane discs surrounded by double membranes.

Ontogenetic changes in spectral sensitivity and retinal topography in the retina of the yellowtail kingfish (Seriola lalandi): Implications for the global Seriola aquaculture industry

The visual environment of several aquaculture species has been shown to be crucial for increased survival and growth. However, very little is known about the visual system of the increasingly popular Seriola genus and its developmental changes. We investigated the ontogenetic changes in colour vision and spatial resolution in the yellowtail kingfish, S. lalandi and discuss them in relation to past behavioural feeding experiments. Microspectrophotometry was used to measure the spectral sensitivities of photoreceptor visual pigments in larvae and sub-adults. The yellowtail kingfish larva has a broad spectral range including ultraviolet-sensitive (UVS) single cones, middle-wavelength-sensitive (MWS) single cones, MWS twin cones and long-wavelength-sensitive (LWS) twin cones. The overall spectral range narrows during development through the loss of the LWS twin cones and a general short-wavelength shift in the spectral sensitivities of the other photoreceptor types. As a sub-adult the yellowtail kingfish also gains a short-wave-sensitive (SWS) single cone. This suggests that different lighting conditions will be optimal for larvae and sub-adults. No changes are observed in retinal ganglion cell (RGC) distribution between juveniles and sub-adults. A temporal concentric increase in RGC density and a weak horizontal band of medium RGC density (30% of the peak density) are present at both stages. This suggests that no changes in the feeding behaviour will occur throughout growth although the sub-adult possesses 1.6 times higher spatial resolution which would increase feeding accuracy at higher pellet densities. Research into the spectral properties of feed types combined with the data obtained here will allow for better contrast between prey and background by optimising lighting conditions.

Cotorsion-free groups from a topological viewpoint

We present a characterization of cotorsion-free abelian groups in terms of homomorphisms from fundamental groups of Peano continua, which aligns naturally with the generalization of slenderness to non-abelian groups. In the process, we calculate the first homology group of the Griffiths twin cone.

Spatial resolving power and spectral sensitivity of the saltwater crocodile, Crocodylus porosus, and the freshwater crocodile, Crocodylus johnstoni

Crocodilians are apex amphibious predators that occupy a range of tropical habitats. In this study, we examined whether their semi-aquatic lifestyle and ambush hunting mode are reflected in specific adaptations in the peripheral visual system. Design-based stereology and microspectrophotometry were used to assess spatial resolving power and spectral sensitivity of saltwater (Crocodylus porosus) and freshwater crocodiles (Crocodylus johnstoni). Both species possess a foveal streak that spans the naso-temporal axis and mediates high spatial acuity across the central visual field. The saltwater crocodile and freshwater crocodile have a peak spatial resolving power of 8.8 and 8.0cyclesdeg(-1), respectively. Measurement of the outer segment dimensions and spectral absorbance revealed five distinct photoreceptor types consisting of three single cones, one twin cone and a rod. The three single cones (saltwater/freshwater crocodile) are violet (424/426 nm λmax), green (502/510 nm λmax) and red (546/554 nm λmax) sensitive, indicating the potential for trichromatic colour vision. The visual pigments of both members of the twin cones have the same λmax as the red-sensitive single cone and the rod has a λmax at 503/510 nm (saltwater/freshwater). The λmax values of all types of visual pigment occur at longer wavelengths in the freshwater crocodile compared with the saltwater crocodile. Given that there is a greater abundance of long wavelength light in freshwater compared with a saltwater environment, the photoreceptors would be more effective at detecting light in their respective habitats. This suggests that the visual systems of both species are adapted to the photic conditions of their respective ecological niche.

Organogenesis of digestive system, visual system and other structures in Atlantic bluefin tuna (Thunnus thynnus) larvae reared with copepods in mesocosm system

Abstract This study examines the anatomical development of Atlantic bluefin tuna during the first month of life at histological level with emphasis in the gut development and those organs required to establish the hunting behaviour characteristic of this species. The tuna larvae have been reared in mesocosm with copepods ( Acartia and Trigriopus sp.) as primary live prey during the first two weeks. The larvae hatched with 3.4 mm average TL and exhibited a very fast growth reaching between 4 and 5 cm at the end of the first month. The yolk reserves were consumed rapidly in two days. As an altricial species the gut and most of the sensory organs were not developed at hatching. The transformation of the gut from an undifferentiated canal at hatching up to a complex and segmented juvenile-like digestive tract occurred in three weeks. At hatching, the digestive tract appeared as a straight tube dorsal to the yolk-sac. The opening of both mouth and anus occurred at 2 days post-hatching (dph). From 4 dph onwards, intestinal loops started to be visible and the primordial future stomach started to develop. Intestinal brush border and increased folds in length were detected in the intestine from 4 dph. Acidophilic protein supranuclear inclusions within the hindgut enterocytes and the first signs of lipid absorption within enterocytes of the anterior intestine were evident from 6 dph. First gastric glands were detected at 11 dph, and at 17 dph the stomach was practically developed with the apparition of the first pyloric caeca. Newly hatched Atlantic bluefin tuna larvae had unpigmented eyes. The eyes were pigmented and functional at the opening of the mouth (between 2 and 3 dph), and rods appeared at 17 dph. Nevertheless twin cones were not observed during the first month. The bluefin tuna larvae quickly acquired a degree of development that allows for efficient predation and digestion of more complex feeds. In fact, the digestive system, sensory and visual structures, thyroid gland, swim bladder, and the kidney and heart differentiated very early during the larval ontogeny of this species, and they were well developed and practically fully functional around 17–18 dph under our rearing conditions. At 21 dph with the change in the allometry of mouth size the post-larvae exhibited most of the juvenile anatomical characteristics.

Comparative Histological Study of the Retina in the Eyes of two Fishes Silurus triostegus Heckel and Liza abu (Heckel)

The present Study Showed that the falciform process and vitereal vessels is extended upper to retina, which are found only in S. triostegus . The visual cells in both fishes have cones and rods with myoid element, myoids are inconspicuous in S. triostegus . The cones in S. triostegus are large but in L. abu found in four types, long single cones, short single cones, dwarf cones and twin cones. It appears that the cones in L. abu arranged as mosaic include square and row patterns, but they are distributed randomly in S. triostegus , also the cones in L. abu have lateral fins which are lack in S. triostegus .The result showed that three types of ganglion cells, long, medium and small as well as there is additional type called Giant ganglion cell found in L. abu .The head of optic nerve has multiple papillae in S. triostegus , while it is smooth in L. abu

Ontogenetic eye development and related behavioural changes in larvae and juveniles of barramundi Lates calcarifer (Bloch)

Larvae and juveniles of barramundi Lates calcarifer (Bloch) were examined for the development of the retina, occurrence of the retinomotor response and retinal tapetum and change in eye size with age in days. The barramundi hatched with unpigmented non-functional eyes in which retinal cells had not yet differentiated into the various elements. Soon it was followed by rapid changes in the histology of the retina. Two-day-old larvae had a well-pigmented retina with area temporalis which would allow acute vision and prey attack in the nasal direction. At 10 days, rod cells and the retinal tapetum first appeared in the retina and the retinomotor response first occurred; these would allow feeding in dim light. The retinal tapetum moved in unison with the cones and the pigment epithelium during the retinomotor response. At 26 days, the horizontal cells were divided into two layers and the twin cones appeared. These changes in the eyes occurred concurrently or in anticipation of behavioural changes, such as the onset of the first feeding at 2 days, the shift of habitat from coastal waters to swamps at the notochord flexion stage at 7–15 days, the abrupt change in feeding behaviour from roving zooplanktivore to lurking predator at 25–30 days and a later shift of habitat from turbid swamps to open coastal or lake areas at the early juvenile stage.

Ocular dimensions and cone photoreceptor topography in adult Nile Tilapia Oreochromis niloticus

Information on the anatomy of the eye and the topography of cone photoreceptor cells in the retina is presented for the Nile Tilapia (Oreochromis niloticus). In adults, the shape and proportions of the ocular components of the prominent eye conform to the general form of fish eyes, as determined using cryo-sectioned eyes. The lens is approximately spherical and there is little variation in the distance from the centre of the lens to the border between the choroid and retina at a range of angles about the optical axis. The average ratio of the distance from the centre of the lens to the retina: lens radius (Matthiessen’s ratio) is 2.44:1. In retinal wholemounts, single and double (twin) cone photoreceptors, forming a square mosaic, are present. Peak photoreceptor densities for both morphological cone types are found in the temporal retina. Using peak cone densities and estimates of focal length from cryo-sectioned eyes, visual acuity is calculated to be 5.44 cycles per deg. The lack of apparent specific ocular or retinal specializations and the relatively low visual acuity reflect the lifestyle of the Nile Tilapia and may allow it to adapt to changes in visual environment in its highly variable natural habitat as well as contributing to the ‘ecological flexibility’ of this species.

Brain and sense organ anatomy and histology of the Falkland Islands mullet, Eleginops maclovinus (Eleginopidae), the sister group of the Antarctic notothenioid fishes (Perciformes: Notothenioidei)

The perciform notothenioid fish Eleginops maclovinus, representing the monotypic family Eleginopidae, has a non-Antarctic distribution in the Falkland Islands and southern South America. It is the sister group of the five families and 103 species of Antarctic notothenioids that dominate the cold shelf waters of Antarctica. Eleginops is the ideal subject for documenting the ancestral morphology of nervous and sensory systems that have not had historical exposure to the unusual Antarctic thermal and light regimes, and for comparing these systems with those of the phyletically derived Antarctic species. We present a detailed description of the brain and cranial nerves of Eleginops and ask how does the neural and sensory morphology of this non-Antarctic notothenioid differ from that seen in the phyletically derived Antarctic notothenioids? The brain of Eleginops is similar to those of visually oriented temperate and tropical perciforms. The tectum is smaller but it has well-developed olfactory and mechanoreceptive lateral line areas and a large, caudally projecting corpus cerebellum. Eye diameter is about twofold smaller in Eleginops than in many Antarctic species. Eleginops has a duplex (rod and cone) retina with single and occasional twin cones conspicuous centrally. Ocular vascular structures include a large choroid rete mirabile and a small lentiform body; a falciform process and hyaloid arteries are absent. The olfactory rosette is oval with 50-55 lamellae, a large number for notothenioids. The inconspicuous bony canals of the cephalic lateral line system are simple with membranous secondary branches that lack neuromasts. In Antarctic species, the corpus cerebellum is the most variable brain region, ranging in size from large and caudally projecting to small and round. "Stalked" brains showing reduction in the size of the telencephalon, tectum, and corpus cerebellum are present in the deep-living artedidraconid Dolloidraco longedorsalis and in most of the deep-living members of the Bathydraconini. Eye diameter is generally larger in Antarctic species but there is a phylogenetic loss of cellularity in the retina, including cone photoreceptors. Some deep-living Antarctic species have lost most of their cones. Mechanosensation is expanded in some species, most notably the nototheniid Pleuragramma antarcticum, the artedidraconid genera Dolloidraco and Pogonophryne, and the deep living members of the bathydraconid tribe Bathydraconini. Reduction in retinal cellularity, expansion of mechanoreception, and stalking are the most noteworthy departures from the morphology seen in Eleginops. These features reflect a modest depth or deep-sea effect, and they are not uniquely "Antarctic" attributes. Thus, at the level of organ system morphology, perciform brain and sensory systems are suitable for conditions on the Antarctic shelf, with only minor alterations in structure in directions exhibited by other fish groups inhabiting deep water. Notothenioids retain a relative balance among their array of senses that reflects their heritage as inshore perciforms.

Effect of light intensity and eye development on prey capture by larval striped bass Morone saxatilis

The efficacy of visual and non‐visual feeding among pelagic striped bass Morone saxatilis larvae adapted to a turbid estuary was determined in the laboratory in clear water. Capture of Artemia salina (density 100 l−1) was significantly affected by the interaction between age of larvae (range: 8–25 days post‐hatch, dph) and light intensity (range: 0–10·6 μmol s−1 m−2 at the water surface). Visual feeding by larvae aged 9–11 dph was highest in dim light (0·086–0·79 μmol s−1 m−2), with fish capturing up to 5 prey larva−1 h−1. As the larvae grew, prey capture in brighter light improved, associated with an increasing proportion of twin cone photoreceptors and improving ability of the retina to light‐ and dark‐adapt. By age >22 dph, mean prey capture was greatest at highest light intensities (0·79 and 10·6 μmol s−1 m−2) exceeding 100 prey larva−1 h−1. Incidence of feeding larvae generally improved as the larvae grew, reaching >80% in all light intensities from 16 dph onwards. The lower threshold for visual feeding, between 0·0084 and 0·03 μmol s−1 m−2, remained constant as the larvae grew, despite an increasing density of rod photoreceptors. Below this threshold, non‐visual feeding was evident at a low rate (<6 prey larva−1 h−1) that was independent of larval age.

Functional Characterization and Molecular Cloning of the K+-dependent Na+/Ca2+ Exchanger in Intact Retinal Cone Photoreceptors

Light-dependent changes in cytoplasmic free Ca2+ are much faster in the outer segment of cone than rod photoreceptors in the vertebrate retina. In the limit, this rate is determined by the activity of an electrogenic Na+/Ca2+ exchanger located in the outer segment plasma membrane. We investigate the functional properties of the exchanger activity in intact, single cone photoreceptors isolated from striped bass retina. Exchanger function is characterized through analysis both of the electrogenic exchanger current and cytoplasmic free Ca2+ measured with optical probes. The exchanger in cones is K+ dependent and operates both in forward and reverse modes. In the reverse mode, the K+ dependence of the exchanger is described by binding to a single site with K1/2 about 3.6 mM. From the retina of the fish we cloned exchanger molecules bassNCKX1 and bassNCKX2. BassNCKX1 is a single class of molecules, homologous to exchangers previously cloned from mammalian rods. BassNCKX2 exists in four splice variants that differ from each other by small sequence differences in the single, large cytoplasmic loop characteristic of these molecules. We used RT-PCR (reverse transcriptase polymerase chain reaction) of individual cells to identify the exchanger molecule specifically expressed in bass single and twin cone photoreceptors. Each and every one of the four bassNCKX2 splice variants is expressed in both single and twin cones indistinguishably. BassNCKX1 is not expressed in cones and, by exclusion, it is likely to be an exchanger expressed in rods.

Computing Prager's Kinematic Hardening Mixed-Control Equations in a Pseudo-Riemann Manifold

Materials' internal spacetime may bear cer- tain similarities with the external spacetime of special relativity theory. Previously, it is shown that material hardening and anisotropy may cause the internal space- time curved. In this paper we announce the third mech- anism of mixed-control to cause the curvedness of inter- nal spacetime. To tackle the mixed-control problem for a Prager kinematic hardening material, we demonstrate two new formulations. By using two-integrating factors idea we can derive two Lie type systems in the product space of M m+1 ⊗M n+1 . The Lie algebra is a direct sum of so(m, 1) ⊕so(n, 1), and correspondingly the symme- try group is a direct product of SOo(m, 1) ⊗SOo(n, 1), which left acts on a twin-cone. Then, by using the one- integrating factor idea we can convert the nonlinear con- stitutive equations into a Lie type system of u Z=CZ with C ∈sl(5, 1,R) a Lie algebra of the special orthochronous pseudo-linear group SL(5, 1,R). The underlying space is a distorted cone in the pseudo-Riemann manifold. Con- sistent numerical methods are then developed according to these Lie symmetries, and numerical examples are used to assess the performance of new algorithms. The measures in terms of the errors by satisfying the consis- tency condition, strain and stress relative errors and ori- entational errors confirm that the new numerical methods are better than radial return method.

RETINAL TWIN CONES OR RETINAL DOUBLE CONES IN FISH: MISNOMER OR DIFFERENT MORPHOLOGICAL FORMS?

Scanning retinal electronmicroscopy studies demonstrated the presence of both twin cones (two identical cones adhered together) and double cones (two non-identical cones adhered together) in the retinae of the major forms of fish, which included actinopterygi, elasmobranch, and teleosts. The complexity of these visual cells in the retinae of different groups of fishes was revealed for the first time and reflected on the diversities of functions of the fish retina in general.

The complexity of the visual cells and visual pathways of the sturgeon

The visual cells in the retinae of the sturgeon were studied by scanning electron microscopy and transmission electron microscopy. Our investigations revealed the presence of rods, two types of single cones, one type of double cone (two nonidentical cone components adhered together), and one type of twin cone (two identical cone components adhered together). In some of the cones, large glycogen bodies were present in the inner segments and all cones contained oil droplets. Such cone morphology was very similar to that described in the retinae of higher vertebrates, for example the chicken. DiI tracing of retinofugal pathways following uniocular injection demonstrated their bilateral localization and extensive termination in the diencephalon and mesencephalon of both sides. Fibers also crossed over from one side to another through commissures, including the posterior commissure. The complexity of the pathway surpassed that of the teleosts and further indicated the evolutionary importance of this fish.