Electrosensitive spatial vectors in elasmobranch fishes: implications for source localization

The electrosense of sharks and rays is used to detect weak dipole-like bioelectric fields of prey, mates and predators, and several models propose a use for the detection of streaming ocean currents and swimming-induced fields for geomagnetic orientation. We assessed pore distributions, canal vectors, complementarity and possible evolutionary divergent functions for ampullary clusters in two sharks, the scalloped hammerhead (Sphyrna lewini) and the sandbar shark (Carcharhinus plumbeus), and the brown stingray (Dasyatis lata). Canal projections were determined from measured coordinates of each electrosensory pore and corresponding ampulla relative to the body axis. These species share three ampullary groups: the buccal (BUC), mandibular (MAN) and superficial ophthalmic (SO), which is subdivided into anterior (SOa) and posterior (SOp) in sharks. The stingray also has a hyoid (HYO) cluster. The SOp in both sharks contains the longest (most sensitive) canals with main projections in the posterior-lateral quadrants of the horizontal plane. In contrast, stingray SO canals are few and short with the posterior-lateral projections subsumed by the HYO. There was strong projection coincidence by BUC and SOp canals in the posterior lateral quadrant of the hammerhead shark, and laterally among the stingray BUC and HYO. The shark SOa and stingray SO and BUC contain short canals located anterior to the mouth for detection of prey at close distance. The MAN canals of all species project in anterior or posterior directions behind the mouth and likely coordinate prey capture. Vertical elevation was greatest in the BUC of the sandbar shark, restricted by the hammerhead cephalofoil and extremely limited in the dorsoventrally flattened stingray. These results are consistent with the functional subunit hypothesis that predicts specialized ampullary functions for processing of weak dipole and geomagnetic induced fields, and provides an anatomical basis for future experiments on central processing of different forms of relevant electric stimuli.     

Morphological comparison of the ampullae of Lorenzini of three sympatric benthic rays

This study investigated and compared the morphology of the electrosensory system of three species of benthic rays. Neotrygon trigonoides, Hemitrygon fluviorum and Maculabatis toshi inhabit similar habitats within Moreton Bay, Queensland, Australia. Like all elasmobranchs, they possess the ability to detect weak electrical fields using their ampullae of Lorenzini. Macroscopically, the ampullary organs of all three species are aggregated in three bilaterally paired clusters: the mandibular, hyoid and superficial ophthalmic clusters. The hyoid and superficial ophthalmic clusters of ampullae arise from both dorsal and ventral ampullary pores. The dorsal pores are typically larger than the ventral pores in all three species, except for the posterior ventral pores of the hyoid grouping. Ampullary canals arising from the hyoid cluster possessed a quasi‐sinusoidal shape, but otherwise appeared similar to the canals described for other elasmobranchs. Ultrastructure of the ampullae of Lorenzini of the three species was studied using a combination of light, confocal and electron microscopy. All possess ampullae of the alveolar type. In N. trigonoides and M. toshi, each ampullary canal terminates in three to five sensory chambers, each comprising several alveoli lined with receptor and supportive cells and eight to 11 sensory chambers in H. fluviorum. Receptor cells of all three species possess a similar organization to those of other elasmobranchs and were enveloped by large, apically nucleated supportive cells protruding well into the alveolar sacs. The luminally extended chassis of supportive cells protruding dramatically into the ampullary lumen had not previously been documented for any elasmobranch species.     

Morphology of the Mechanosensory Lateral Line System in Elasmobranch Fishes: Ecological and Behavioral Considerations

The relationship between morphology of the mechanosensory lateral line system and behavior is essentially unknown in elasmobranch fishes. Gross anatomy and spatial distribution of different peripheral lateral line components were examined in several batoids (Raja eglanteria, Narcine brasiliensis, Gymnura micrura, and Dasyatis sabina) and a bonnethead shark, Sphyrna tiburo, and are interpreted to infer possible behavioral functions for superficial neuromasts, canals, and vesicles of Savi in these species. Narcine brasiliensis has canals on the dorsal surface with 1 pore per tubule branch, lacks a ventral canal system, and has 8–10 vesicles of Savi in bilateral rows on the dorsal rostrum and numerous vesicles ( = 65 ± 6 SD per side) on the ventral rostrum. Raja eglanteria has superficial neuromasts in bilateral rows along the dorsal body midline and tail, a pair anterior to each endolymphatic pore, and a row of 5–6 between the infraorbital canal and eye. Raja eglanteria also has dorsal canals with 1 pore per tubule branch, pored and non-pored canals on the ventral surface, and lacks a ventral subpleural loop. Gymnura micrura has a pored dorsal canal system with extensive branch patterns, a pored ventral hyomandibular canal, and non-pored canal sections around the mouth. Dasyatis sabina has more canal pores on the dorsal body surface, but more canal neuromasts and greater diameter canals on the ventral surface. Sphyrna tiburo has primarily pored canals on both the dorsal and ventral surfaces of the head, as well as the posterior lateral line canal along the lateral body surface. Based upon these morphological data, pored canals on the dorsal body and tail of elasmobranchs are best positioned to detect water movements across the body surface generated by currents, predators, conspecifics, or distortions in the animal's flow field while swimming. In addition, pored canals on the ventral surface likely also detect water movements generated by prey. Superficial neuromasts are protected from stimulation caused by forward swimming motion by their position at the base of papillar grooves, and may detect water flow produced by currents, prey, predators, or conspecifics. Ventral non-pored canals and vesicles of Savi, which are found in benthic batoids, likely function as tactile or vibration receptors that encode displacements of the skin surface caused by prey, the substrate, or conspecifics. This mechanotactile mechanism is supported by the presence of compliant canal walls, neuromasts that are enclosed in wide diameter canals, and the presence of hair cells in neuromasts that are polarized both parallel to and nearly perpendicular to the canal axis in D. sabina. The mechanotactile, schooling, and mechanosensory parallel processing hypotheses are proposed as future directions to address the relationships between morphology and physiology of the mechanosensory lateral line system and behavior in elasmobranch fishes.     

Interrelations between auditory and vestibular receptors in the frog's labyrinth

Summary The influence of the efferent vestibular system being eliminated, the spontaneous activity of afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By functionally eliminating either both papillae or all the vestibular receptors except for the papillae, and then using statistical methods, as well as by stimulating the papillae by sounds or the papillary nerve fibres by electrical stimulus, it has been shown that the auditory papillae have a facilitatory influence on the spontaneous afferent activity from the horizontal and vertical anterior canals. This influence is most likely mediated by receptor-receptor fibres arising from the auditory organs and innervating the semicircular canals.Abbreviations HC horizontal canal - VAC vertical anterior canal This research was supported by a grant from D.G.R.S.T. (Aide à la Recherche n 77.7.1127)     

Ampullary organ morphology of freshwater salmontail catfish, Arius graeffei

Two types of ampullary organs are present in the skin of the freshwater salmontail catfish, Arius graeffei, each consisting of a short canal (0.2-0.5 mm) oriented perpendicular to the basement membrane and ending in an ampulla. Histochemical staining techniques (Alcian blue and Lillie's allochrome) indicate that the ampullary canals contain an acidic mucopolysaccharide gel, which is uniform in its staining properties along the canals. Type II ampullary organs consist of a canal, the wall of which is lined with cuboidal epithelial cells. The canal opens into an ampulla with 50-60 receptor cells. Electron microscopy reveals that the pear-shaped receptor cells bear microvilli on their luminal surface and lie adjacent to an unmyelinated neuron. Type III ampullary organs differ from Type II in that the canal wall consists of cells that possess a protein-rich sac at the luminal apex and have a polymorphic nucleus. The canals of Type III ampullary organs open to an ampulla with 8-30 receptor cells similar in both staining properties and structure to those of the Type II organ. In both types of ampullary organs, supportive cells surround each receptor cell except at the apex of the receptor cell.     

Comparison of the lateral line and ampullary systems of two species of shovelnose ray

The anatomical characteristics of the mechanoreceptive lateral line system and electrosensory ampullae of Lorenzini of Rhinobatos typus and Aptychotrema rostrata are compared. The spatial distribution of somatic pores of both sensory systems is quite similar, as lateral line canals are bordered by electrosensory pore fields. Lateral line canals form a sub-epidermal, bilaterally symmetrical net on the dorsal and ventral surfaces; canals contain a nearly continuous row of sensory neuromasts along their length and are either non-pored or pored. Pored canals are connected to the surface through a single terminal pore or additionally possess numerous tubules along their length. On the dorsal surface of R. typus, all canals of the lateral line occur in the same locations as those of A. rostrata. Tubules branching off the lateral line canals of R. typus are ramified, which contrasts with the straight tubules of A. rostrata. The ventral prenasal lateral line canals of R. typus are pored and possess branched tubules in contrast to the non-pored straight canals in A. rostrata. Pores of the ampullae of Lorenzini are restricted to the cephalic region of the disk, extending only slightly onto the pectoral fins in both species. Ampullary canals penetrate subdermally and are detached from the dermis. Ampullae occur clustered together, and can be surrounded by capsules of connective tissue. We divided the somatic pores of the ampullae of Lorenzini of R. typus into 12 pore fields (10 in A. rostrata), corresponding to innervation and cluster formation. The total number of ampullary pores found on the ventral skin surface of R. typus is approximately six times higher (four times higher in A. rostrata) than dorsally. Pores are concentrated around the mouth, in the abdominal area between the gills and along the rostral cartilage. The ampullae of both species of shovelnose ray are multi-alveolate macroampullae, sensu Andres and von Düring (1988). Both the pore patterns and the distribution of the ampullary clusters in R. typus differ from A. rostrata, although a basic pore distribution pattern is conserved.     

Infrastructure in the electric sense: admittance data from shark hydrogels

Elasmobranchs (sharks, skates, and rays) possess an electrosensory system with an infrastructure of canals connecting the electrosensors to the environment. The electrosensors and canals are filled with a uniform hydrogel, but the gels function has not yet been determined. We present electrical admittance spectra collected from the hydrogel from 0.05 to 100 kHz, covering the effective range of the electrosensors. We have taken samples of this gel, postmortem, from Triaenodon obesus and Carcharodon carcharias; for purposes of comparison, we have synthesized a series of collagen-based hydrogel samples. The shark hydrogels demonstrate suppressed admittance when compared to both seawater and collagen gels. In particular, collagen hydrogels with equivalent ion concentrations are roughly 2.5 times more polarizable than the shark samples. We conclude that the shark hydrogels strongly localize ionic species, and we discuss the implications for the related roles of the gel and the canals in the electric sense. The gel-filled canals appear better suited to fostering voltage differences along their length than to providing direct electrical contact to the seawater environment.     

Morphology of the teleost ampullary organs in marine salmontail catfish Neoarius graeffei (Pisces: Ariidae) with comparative analysis to freshwater and estuarine conspecifics

We hypothesized that due to the relative conductivity of the environment, and to maintain sensory function, ampullary organs of marine Neoarius graeffei would differ morphologically from those described previously for estuarine and freshwater conspecifics. Unlike the ampullary systems of N. graeffei from freshwater and estuarine habitats, the ampullary pores of marine specimens occur in two distinct patterns; numerous pores seemingly randomly scattered on the head and ventro‐lateral regions of the body, and pores arranged in distinctive vertical lines above the lateral line on the dorso‐lateral body of the fish. Light and electron microscopy revealed that the ampullary organs also differed morphologically from estuarine and freshwater specimens in the presence of longer ampullary canals, a hitherto unreported canal wall composition, and in the collagen sheath surrounding both the canal and the ampulla proper within dermal connective tissues. Ampullary pores were wider in marine individuals and opened to the longest ampullary canals reported for this species. The canal wall was lined by cuboidal and squamous epithelial cells. Each ampullary canal opened into a single ampulla proper containing significantly more receptor cells than estuarine and freshwater conspecifics. The distribution of ampullary pores as well as the microstructure of the ampullary organs indicates that the electrosensory system of marine N. graeffei differs from those of estuarine and freshwater specimens in ways that would be expected to maintain the functionality of the system in a highly conductive, fully marine environment, and reveals the remarkable plasticity of this species’ ampullary system in response to habitat conductivity. J. Morphol. 276:1047–1054, 2015. © 2015 Wiley Periodicals, Inc.     

The cerebellar dorsal granular ridge in an elasmobranch has proprioceptive and electroreceptive representations and projects homotopically to the medullary electrosensory nucleus

1. Response properties of neurons in the dorsal granular ridge (DGR) of the little skate, Raja erinacea, were studied in decerebrate, curarized fish. Sensory responses included proprioceptive (426 of 952; 45%) and electroreceptive units (526 of 952; 55%). Electroreceptive units responded to weak electric fields with a higher threshold than lower-order units and had large ipsilateral receptive fields, whose exact boundaries were often unclear but contained smaller, identifiable best areas. Proprioceptive units responded to displacement of the ipsilateral fin and were either position-or movement-sensitive.
2. Both proprioceptive and electroreceptive units showed a progression of receptive fields from anterior to posterior body in the rostral to caudal direction along the length of DGR. Sensory maps in DGR projected homotopically to the electrosensory somatotopy in the dorsal nucleus. Peak evoked potentials and units responding to local DGR stimulation occurred only in areas of the dorsal nucleus with receptive fields located within the composite receptive field at the DGR stimulation site.
3. Single shocks to DGR produced a short spike train followed by a prolonged suppression period in the medullary dorsal nucleus. These results have implications for the role of the parallel fiber system in medullary electrosensory processing.

     

Annulate lamellae and chromatoid bodies in the testes of a cyprinid fish (Pimephales notatus)

Summary Observations on annulate lamellae and chromatoid bodies in spermatogonia of the cyprinid fish Pimephales notatus have revealed several commonly occurring features heretofore unreported: These include (a) the presence of annulate lamellae in close association with chromatoid bodies; (b) the existence of a chromatoid band or shell between the nuclear envelope and some chromatoid bodies with connections among them; (c) the presence of annulate pore complexes in the absence of well developed membrane envelopes as well as in association with such envelopes; (d) the presence of material just outside the nucleus and contiguous with nuclear pores which is of a similar density and texture to that of the chromatoid bands and chromatoid bodies; (e) filamentous material between the cytoplasmic sides of nuclear pores and the chromatoid band, bridging a distance of approximately 1000 Å and similar threads extending a like distance between chromatoid bodies (and bands) and annulate lamellae associated with them; and (f) mitochondria closely arranged about some chromatoid bodies.     

Backfilling canals to restore wetlands: empirical results in coastal Louisiana

Wetland restoration is largely a developing science and engineering enterprise. Analyses of results are too few and constrained to observations over a few years. We report here on the effectiveness of one restoration technique used sparsely in coastal Louisiana for several decades. Canals have been dredged in coastal Louisiana wetlands since 1938 for oil and gas exploration and extraction. These canals are typically dredged to 2.5 m depth and are 20 to 40 m wide. Canal lengths vary from 100 m to several 1000s m in the case of outer continental shelf pipeline canals that cross the wetlands.Today, thousands of miles of canals crisscross these wetlands. Studies have linked dredged canals to a number of undesirable effects on the wetland environment including alterations in salinity, flooding and drainage patterns, direct loss of marsh by convention to open water, and increases in marsh erosion rates. These effects have led state and federal agencies charged with managing the wetland resource to look for methods of mitigating canal impacts. One possible method of managing spoil banks after the abandonment of a drilling site is to return spoil material from the spoil banks to the canal with the hope that marsh vegetation will be reestablished on the old spoil banks and in the canal. The movement of former spoil bank material back into the canal is referred to as backfilling.The purpose of this study was to (1) examine how backfilled canals changed over 10 years, (2) examine factors influencing success with multiple regression statistical models, and, (3) compare costs of backfilling with other Louisiana marsh restoartion projects. We examined the sites to document and interpret changes occurring since 1983/4 and to statistically model the combined data derived from these new and previous analyses. Specifically, we wanted to determine the recovery rates of vegetation, water depth, and soils in backfilled canals, restored spoil banks, and in nearby marshes, and to quantify the influence of plugging canals on these rates.The major factors determining backfilling restoration success are the depth of the canal, soil type, canal dimensions, locale, dredge operator skill, and permitting conditions. Plugging the canal has no apparent effect on water depth or vegetation cover, with the exception that submerged aquatic vegetation may be more frequently observed behind backfilled canals with plugs than in backfilled canals without plugs. Canal age, soil organic matter content, and whether restoration was done as mitigation on-site or off-site were the most important predictors of final canal depth. Canal length and percentage of spoil returned (+) had the greatest effect on the restoration of vegetation cover. Backfilled canals were shallower if they were older, in soils lower in organic matter, and backfilled off-site. Backfilling the canal restores wetlands at a cost of $1,200 to $3,400/ha, which compares very favorably with planned restoration projects in south Louisiana.Corresponding Editor: Anonumous     

The architecture of the canal systems of Petrosia ficiformis and Chondrosia reniformis studied by corrosion casts (Porifera,Demospongiae)

Summary The three-dimensional organization of the canal system in two sponge species, Petrosia ficiformis and Chondrosia reniformis, was studied using corrosion casts. Casts were made of live animals, in situ, and canal replicas were analzyed by scanning electron microscopy (SEM). In P. ficiformis the incurrent system consists of a superficial canal network giving rise to large radial canals, which ramify and anastomosize forming an internal web. Excurrent canals are arranged into modular ramified systems radiating from atrial cavities opening to the exterior. Main excurrent canals run at various depths within the sponge, even through the superficial incurrent network. Both incurrent and excurrent canal replicas show smooth, blind-ending capillaries. Some large incurrent canals merge with excurrent ones, thus bypassing choanocyte chambers. In C. reniformis there is a cortical collagen layer crossed by three-like incurrent canals, the twigs of which communicate with groups of inhalant pores. The stems of tree-like canals penetrate into the sponge medulla where they ramify and anastomosize to form a web. Main excurrent canals arise from large cloacal ducts leading to the oscular openings. They give rise to a sequence of branches intersecting the incurrent web. Both incurrent and excurrent canals have sharp, blind-ending capillaries. Morphometric data functions show that diameter scaling in canal branches is exponential in Petrosia and linear in Chondrosia. Structural differences and homologies between the two species are discussed.     

End buds: non-ampullary electroreceptors in adult lampreys

Summary Shared anatomical and physiological characters indicate that the low-frequency sensitive electrosensory system of lampreys is homologous with those of non-teleost fishes and amphibians. However, the ampullary electroreceptor organs which characterize all of these gnathostomes are not found in lampreys. Experimental anatomical and physiological studies reported here demonstrate that the epidermal end buds are the electroreceptors of adult lampreys.End buds, consisting of both sensory and supporting cells, are goblet-shaped with the top (25–60 m diameter) at the epidermal surface and the stem directed toward the dermis (Fig. 1A). Short lines or clusters of 2–8 end buds (Fig. 1B) are distributed over both trunk and head. Injections of horseradish peroxidase (HRP) into vitally-stained end buds labeled anterior lateral line afferents terminating in the ipsilateral dorsal nucleus (Fig. 2A) — the primary electrosensory nucleus of the lamprey medulla. Conversely, after HRP injection into the dorsal nucleus HRP-filled fibers and terminals were present on ipsilateral end buds (Fig. 2B).End buds are usually not visible without staining. However, in adult sea lampreys the presence of end buds was histologically confirmed in skin patches containing the receptive fields of electroreceptor fibers recorded in the anterior lateral line nerve. Additionally, in the rare instance of two silver lampreys in which end buds were visible without staining, electrosensory activity indistinguishable from that of the primary electroreceptor afferents was recorded from the end bud surface (Figs. 3, 4).End buds were initially characterized as chemoreceptors (Johnston 1902) but were later correctly advanced as lateralis receptors based on the presence of presynaptic dense bodies in the receptor cells (Whitear and Lane 1981). Unlike all other low-frequency electroreceptors, end buds lack canals. The receptor cells contact the epidermal surface and possess apical microvilli rather than the kinocilium of most gnathostomes with homologous electrosensory systems of the primitive (non-teleost) type.Larval lampreys and newly transformed adults lack end buds although at least the latter are electroreceptive. End buds, therefore, may be the form taken by electroreceptors only in the final portion of a lamprey's life.     

Distribution and morphology of the ampullary organs of the salmontail catfish,Arius graeffei

Whole body staining of Arius graeffei revealed that ampullary pores cover the body with their highest densities occurring on the head and lowest densities on the mid‐ventral surface. Each ampullary organ consists of a long canal (0.2–1.75 mm) passing perpendicular to the basement membrane, through the epidermis into underlying dermal connective tissues, curving thereafter to run roughly parallel to the epidermis. Histochemical staining techniques (Alcian blue and Lillie′s allochrome) indicate that the canals contain a neutral to acidic glycoprotein‐based mucopolysaccharide gel that varies in composition along the length of the canal. Collagen fibers, arranged in a sheath, surround a layer of squamous epithelium that lines each ampullary canal. At the proximal end of the canal, squamous cells are replaced by cuboidal epithelial cells that protrude into the lumen, thus constricting the lumen to form a small pore into the ampulla. The ampulla is lined with receptor and supportive cells. The numerous (60–120) pear‐shaped receptor cells bear microvilli on their luminal surface. Two forms of receptor cells exist in each ampullary organ: basal and equatorial receptor cells. Each receptor cell is connected to an unmyelinated nerve. Each receptor cell is surrounded by supportive cells on all but the apex. Tight junctions and underlying desmosomes occur between adjacent receptor and supportive cells. This form of ampullary organ has not previously been described for teleosts. J. Morphol. 239:97–105, 1999. © 1999 Wiley‐Liss, Inc.     

Pore canals in the cornea of a functionally specialized area of the honey bee's compound eye

Summary The fine structure of the cornea in an anatomically and functionally specialized part of the honey bee's compound eye (dorsal rim area) was examined by light microscopy, transmission electron and scanning electron microscopy. Under incident illumination the cornea appears grey and cloudy, leaving only the centers of the corneal lenses clear. This is due to numerous pore canals that penetrate the cornea from the inside, ending a few m below the outer surface. They consist of (1) a small cylindrical cellular evagination of a pigment cell (proximal), and (2) a rugged-walled, pinetree-shaped extracellular part (distal). The functional significance of these pore canals is discussed. It is concluded that their light scattering properties cause the wide visual fields of the photoreceptor cells measured electrophysiologically in the dorsal rim area, and that this is related to the way this eye region detects polarization in skylight.     

The elasmobranch spiracular organ

Summary The spiracular organ is a lateral line derived receptor associated with the first gill cleft (spiracle). Its functional morphology was studied in the little skate,Raja erinacea, and a shark, the smooth dogfish,Mustelus canis, with light and electron microscopy. The spiracular organ is a tube (skate) or pouch (shark) with a single pore opening into the spiracle. The lumen is lined with patches of sensory hair cells, and filled with a gelatinous cupula. In the little skate, hair cells form synapses with afferents but apparently not with efferent fibers. In both species, the spiracular organs are deformed by flexion of the hyomandibular cartilage at its articulation with the cranium. The hyomandibula is a suspensory element of the jaws; hyomandibular flexion results in jaw protrusion. The little skate spiracular organ is anchored at one end to the cranium and at the other to the hyomandibula so that it is stretched or relaxed during hyomandibular extension and flexion, respectively. InMustelus, the effects of hyomandibular flexion on the spiracular organ are mediated indirectly by the superior post-spiracular ligament which inserts on the distal end of the hyomandibula. Deformation of the dogfish shark cupula during hyomandibular movement was observed. In the little skate, as revealed by transmission electron microscopy, there is a measurable deflection of the hair cell ciliary bundles from spiracular organs fixed with the hyomandibula in the flexed relative to the extended positions. In both species, hyomandibula flexion should result in hair cell depolarization, and sensory afferent excitation, based on the direction of the observed (skate) or expected (shark) deflection of hair cell cilia.     

Hyoid and pharyngeal arch function during ventilation and feeding in elasmobranchs: Conservation and modification in function

The hypothesis that the mandibular and hyoid arches evolved from anterior pharyngeal arches to increase ventilation performance and subsequently became adapted for feeding is widely accepted. As jaws evolved, the morphology of the hyoid arch changed notably from that of a pharyngeal arch. Furthermore, hyoid arch morphology varies considerably among elasmobranch taxa and has been shown to be related to feeding style. The goal of this study is to determine whether the function (direction of movement or change in cavity cross‐section) of the hyoid arch is altered from that of the pharyngeal arch, and whether function is altered between ventilation, the basal behavior, and feeding, the derived behavior. Similar effects and associations of the pharyngeal arches by orientation to feeding or ventilation are also investigated. The kinematics of the hyoid and second pharyngeal arch during ventilation and feeding are quantified using sonomicrometry and hyomandibular angle measured in five shark and one skate species representing widely divergent hyomandibular morphologies. Hyoid and pharyngeal cavity width follows the same pattern of movement during ventilation; therefore the hyoid arch retains the ancestral function of the pharyngeal arches. The orientation of the hyomandibular cartilage appears to influence the pattern of arch movement during ventilation: anterior directed elements decrease in cavity width; laterally directed elements increase in cavity width; while posterior directed elements increase in cavity width or do not change; while cavity depth increases in all species. Hyoid and pharyngeal cavity width movement differs among the species during feeding and also appears to be related to hyoid arch orientation as well as feeding style. There appears to be a division between those species with hyomandibular angles less than 110° from those that are greater between feeding mode and hyoid cavity width movement. Primarily suction feeding species decrease hyoid cavity width whereas primarily bite feeding species increase hyoid cavity width during feeding while all species increase hyoid cavity depth.     

Ascending spinal systems in the nurse shark,Ginglymostoma cirratum

Summary The ascending spinal systems in the nurse shark were studied after spinal hemisections by use of the Nauta and Fink-Heimer techniques. The dorsal funicular fibers form a single bundle issuing fibers to the gray substance of the spinal cord, the dorsal funicular nucleus, and the vestibular complex. Some dorsal funicular fibers also appear to contribute to the spinocerebellar tract.The degenerated lateral funicular fibers are segregated into three fasciculi issuing fibers medially as they ascend through the brainstem. The largest target of these fibers is the reticular formation, but diffusely organized axons also reach 1) the gray matter of the spinal cord, 2) the dorsal motor nucleus of the vagus, 3) the nucleus A of the medulla oblongata, 4) the central gray substance of the brainstem, 5) the cerebellar cortex, 6) the cerebellar nucleus, 7) the nucleus intercollicularis, 8) the mesencephalic tectum, and 9) the dorsal thalamus. At the latter site the spinal input appears to partly overlap with the visual input.The results, compared with the strikingly similar findings in other classes of vertebrates, indicate that all vertebrate groups apparently have the same basic components of ascending spinal projections.     

Chemosensory integration in the spiny lobster: Ascending activity in the olfactory-globular tract

Summary In the frog,Rana esculenta, when the influence of the efferent vestibular system was eliminated, the spontaneous activity of single afferent fibres recorded from one branch of the nerve of the horizontal semicircular canal (HC) or of the nerve of the vertical anterior canal (VAC) was inhibited in 16–17% of the cases when stimulating electrically the other branch of the same ampullary nerve. Moreover, the spontaneous activity of about 200 afferent fibres was recorded from the nerves of the HC and VAC in three experimental situations. In the first one, the brain was destroyed, or the left vestibular nerve cut as it enters the brain stem, and all the branches of the left vestibular nerve were cut except for the one recorded (VAC or HC nerve); in the second one, recordings were made on the peripheral end of the ampullary nerve previously cut near the ampulla; in the third situation they were made on the ampullary nerve after having cut the vestibular nerve between the periphery and Scarpa's ganglion close to Scarpa's ganglion. Statistical comparisons of the distribution of the spontaneous frequencies and of the mean activities between the experimental situations show that the activities were greater in the second or third experimental situations than in the first one. These results could be explained by the existence of an inhibitory feedback loop outside the brain including Scarpa's ganglion and mediated by receptor-receptor fibres.Abbreviations HC horizontal semicircular canal - PE peripheral end of the ampullary nerve - VAC vertical anterior semicircular canal This research was supported by a grant from D.G.R.S.T. (Aide à la Recherche n 77.7.1127)     

Studies on the nephron of an elasmobranch fish Scyliorhinus stellaris (L.)

Summary The nephron of the elasmobranch Scyliorhinus stellaris was studied by macerating kidneys of newly hatched specimens in a solution of arsenic anhydride and by sectioning material of the same age and of late embryos. It was found that each nephron consists of (a) a dorsal conical portion containing a skein of canals, loosely intertwined and immersed in blood sinuses, (b) a Malpighian corpuscle, (c) a ventral portion formed by a tightly packed bundle of five tubules. It was not possible to disentangle the ventral tubules so as to recognize their sequence. It may be stated that the neck, originating from the corpuscle and coming back to it after a bend, forms two of such tubules; two more are similarly connected at the distal end by another loop; one forms the collecting duct. The dorsal part of the nephron contains two canals, greatly folded and interlaced. When completely dissociated they appeared to consist of (a) a larger and longer one, corresponding to the brush border portion of all vertebrates (it is thick for most its length, but becomes thin at one end), and (b) a smaller and shorter one, lined by low cells throughout, with no brush border. Although it is not possible to decide so far which of these canals precedes the other, it was ascertained that they are not continuous with each other inside the dorsal portion, but are connected by means of a loop situated in the ventral bundle. The renal tubule passes by, and adheres to the corpuscle four times. The small dorsal canal, although it does not correspond, either in topography or in structure, to the features of the alleged special segments, may be something peculiar to elasmobranchs.Dedicated to Professor Wolfgang Bargmann on his 60th birthday. — Research carried out under contracts with the U. S. Atomic Energy Commission (NYO-3355-3) and Euratom (043-65-1 BIOI), and supported by the Italian C. N. R. and Ministry of Education. — Thanks are due to Dr. P. Dohrn and the staff of the Zoological Station for their help in securing the material and to Dr. Elena Vivori who revised the English.