bluuebunny/crossref_metadata_2025 huggingface dataset:
Coxal Muscle Receptors in the Crab: the Receptor Potentials of S and T Fibres in Response to Ramp Stretches
Authors: Bush B. M. H. , Roberts Alan
Published: April 2021

Intracellular and extracellular recordings from the two large-diameter S and T sensory fibres of the posterior thoracico-coxal muscle receptor in shore crabs confirm the graded, dynamic-static nature of the receptor potentials evoked by stretching the receptor muscle, and the lack of afferent impulses. Slow ramp-function stretches evoke receptor potentials with characteristic shapes, which differ between the two fibres in several respects: The dynamic component in the S fibre resembles an algebraic sum of length and velocity responses and a variable initial ‘acceleration’ (?) transient, while in the T fibre it commonly declines (‘adapts’) during stretching, especially at greater velocities and starting lengths. On release of stretch the S fibre usually exhibits a ‘negative velocity response’, but the T fibre repolarizes rapidly often with a slight hyperpolarization. The dynamic response of the T fibre is generally greater than that of the S fibre, and increases more steeply and approximately logarithmically with stretch velocity over a 10- to 50-fold range. The’ static response ‘or degree of depolarization increases fairly linearly with receptor length in the S fibre but very non-linearly in the T fibre. The T fibre displays pronounced hysteresis in its dynamic and static responses at increasing and decreasing lengths, but the S fibre shows little hysteresis. The T fibre but not the S fibre commonly shows small rapid oscillations or ‘noise’ superimposed upon strongly depolarized ‘static’ potentials. The S and T responses may be affected reciprocally by some forms of receptor muscle contraction. Graded receptor potentials evoked in the ‘D’ fibre by stretching the non-muscular depressor-receptor strand of the coxo-basal joint show little hysteresis. Receptor muscle fibres respond to motor nerve stimulation or spontaneous motor impulses from the thoracic ganglion with slow, facilitating and summating excitatory junctional potentials. The mechanisms underlying the differences between S and T responses, and their functional significance to the animal, are discussed, and comparisons are drawn with other muscle receptors.
Experiments with the Isolated Heart of the Gastropod Helix Pomatia in an Artificial Pericardium
Authors: Civil G. W. , Thompson T. E.
Published: April 2021

Isolated hearts of Helix pomatia could be maintained for 3–4 days at 19 °C in physiological saline. Co-ordination was soon lost, but irregular twitches could be observed for up to 115 h. A perfusion apparatus was designed which supplied a simulated venous return pressure of 8 cm saline and enabled in vitro survival of pericardium-free hearts for up to 2 days at 15 °C. Cessation of perfusion led immediately to a reversible stoppage of heart-beat. An artificial pericardium apparatus (APA) allowed the role of the pericardium to be studied. In the APA measurable translocation of fluid was effected by the heart, even when the simulated venous return pressure was negative. If the APA was transformed into an open system by opening up a simulated reno-pericardial canal, the effectiveness of the heart was greatly reduced. In the APA the greater the dilation of the heart (in consequence of decreased volume of pericardial fluid) the greater was the stroke volume for a given simulated venous return pressure. Results obtained with the APA give support to the theory that in the gastropod heart the filling of the auricle is hydrodynamically coupled (through the pericardial fluid) to the emptying of the ventricle.
Factors Affecting Blood Flow to the Lungs in the Amphibian, Xenopus Laevis
Authors: Emilio M. G. , Shelton G.
Published: April 2021

A series of breathing movements which are effective in ventilating the lungs are accompanied by a marked increase in pulmonary blood flow and a decrease in pulmo-cutaneous arterial pressure. This reaction must involve considerable vasodilation of the pulmonary vascular bed. Similar vasodilation is produced by artificial inflation of the lungs via an implanted cannula. Nitrogen is not so effective as air in producing the vasodilation, whereas oxygen is more effective. It is suggested that both stretch receptors in the lungs and chemical receptors in lungs or blood are involved in the reaction. The level of anaesthesia is important in determining the degree of vasodilation response to the different stimuli. It is concluded that the central nervous system is the site where interaction occurs between signals from stretch receptors and chemical receptors and from the breathing movements themselves. Experiments with atropine suggest that the efferent pathway is in the vagus nerve. Recordings from free-swimming, unanaesthetized toads show that the vasodilation response occurs as part of normal diving-emergence behaviour.
Energetics of Hovering Flight in Hummingbirds and in Drosophila
Authors: Weis-Fogh Torkel
Published: April 2021

Expressions have been derived for an estimate of the average coefficient of lift, for the variation in bending moment or torque caused by wind forces and by inertia forces, and for the power output during hovering flight on one spot when the wings move according to a horizontal figure-of-eight. In both hummingbirds and Drosophila the flight is consistent with steady-state aerodynamics, the average lift coefficient being 1·8 in the hummingbird and o-8 in Drosophila. The aerodynamic or hydraulic efficiency is 0·5 in the hummingbird and 0·3 in Drosophila, and in both types the aerodynamic power output is 22–24 cal/g body weight/h. The total mechanical power output is 39 cal g−1 h−1 in the hummingbird because of the extra energy needed to accelerate the wing-mass. It is 24 cal g−1 h−1 in Drosophila in which the inertia term is negligible because the wing-stroke frequency is reduced to the lowest possible value for sustained flight. In both animals the mechanical efficiency of the flight muscles is 0·2. It is argued that the tilt of the stroke plane relative to the horizontal is an adaptation to the geometrically unfavourable induced wind and to the relatively large lift/drag ratio seen in many insects. The vertical movements at the extreme ends may serve to reduce the interaction between the shed ‘stopping’ vortex and the new bound vortex of opposite sense which has to be built up during the early part of the return stroke. Two additional non-steady flow situations may exist at either end of the stroke, delayed stall and delayed build-up of circulation (Wagner effect), but since they have opposite effects it is probable that the resultant force is of about the same magnitude as that estimated for a steady-state situation. Most insects have an effective elastic system to counteract the adverse effect of wing-inertia, but small fast-moving vertebrates have not. It is argued that the only material available for this purpose in this group is elastin and that it is unsuited at the rates of deformation required because recent measurements have shown that the damping is relatively high, probably due to molecular factors.
Electrophysiological Studies on the Heart of the Bivalve Mollusc,Modiolus Demissus
Authors: Wilkens Lon A.
Published: April 2021

The membrane potential in the heart of Modiolus demissus is dependent primarily on the unequal distribution of potassium ions across the cell. The membrane potential is low, however, and the reduced slope of the potassium equilibrium potential is not predictable by the familiar Nemst equation. The membrane undergoes a sustained depolarization in Cl-free SW which reduces the magnitude of subsequent potassium depolarization. Chloride ions contribute, perhaps independently, up to 15–30% of the total potential. The high degree of variability in membrane potential is due, in part, to a sodium leakage current. Membrane hyperpolarization in Na-free SW is greatest in hearts with a low initial potential. An electrogenic sodium pump is described which contributes to the membrane potential in the form of a rhythmical after-hyperpolarization (positive after-potential) following each spike. Inhibition of the pump (reduction of the after-potential) can be achieved using ouabain and cyanide, by substituting lithium for sodium, by removing extracellular potassium and by cooling the heart. The ionic basis of the membrane potential is discussed in relation to the diffuse pacemaker properties of the heart.
The Mode of Action Of 5-Hydroxytryptamine
Authors: Berridge M. J.
Published: April 2021

The isolated salivary gland of the blowfly Calliphora has been used to study the molecular pharmacology of 5-hydroxytryptamine (5-HT). Ethylamine alone is inactive but the addition of extra carbon atoms or ring systems (imidazole or benzene) introduces some activity. A 5-hydroxyindole ring confers most activity. If the hydroxyl group is either removed, replaced with other groups, or displaced to the 4- or 6-position on the indole ring there is a large reduction in activity. The activity of the molecule is greatly reduced if the length of the side chain is decreased (gramine) or increased (3-aminopropyl indole) by a single carbon atom. Such molecules are effective competitors. These structure-activity studies suggest that the specificity of 5-HT resides in the 5-hydroxyindole moiety which binds the molecule to the receptor while the positively charged ethylamine side chain is responsible for inducing the hormonal effect.
The Effects of 5-Hydroxytryptamine and Cyclic Amp on the Potential Profile across Isolated Salivary Glands
Authors: Prince William T. , Berridge Michael J.
Published: April 2021

The sites of the transepithelial potential changes produced by 5-HT and cyclic AMP in the salivary gland of the blowfly (Calliphora) have been investigated. Microelectrodes recorded a two-step potential profile across this epithelium. The cell was negative to both the bathing medium and the saliva. The basal membrane potential was 44·0 ± 0·2 mV and was affected very little by application of either 5-HT or cyclic AMP. The apical membrane was depolarized by 5-HT and in contrast was hyperpolarized by cyclic AMP. On the basis of these results it is concluded that 5-HT has two actions: (a) to stimulate a potassium pump on the apical membrane using cyclic AMP as an intermediary, (b) to increase chloride movement by a mechanism not directly involving cyclic AMP.
Aspects of Branchial Irrigation in the Lobster Homarus Americanus
Authors: Wilkens J. L. , McMahon B. R.
Published: April 2021

The movements of the scaphognathites of the lobster, Homaros americanos, and the resulting thrust, were resolved in two dimensions accompanied by attack angle changes. Correlation of these scaphognathite and related body movements with branchial hydrostatic pressures during forward and reversed pumping were effected by simultaneously recording on video tape. Forward pumping maintains a negative pressure within the branchial chambers of 2·5–10 mm H2O superimposed on a maintained negative pressure relative to the outside of 0·5 mm H2O. The scaphognathite, by assuming a negative attack angle to the water during the upstroke of the beat, produces the positive pressure of reversals. Contraction of the epimeral attractor muscle appears to contribute to the re-establishment of branchial negativity following each reversal. This muscle inserts on the epimera and by contraction enlarges the branchial chamber. The role of reversals is discussed and it is concluded that their primary function is to clean foreign material from the border of hairs which filter incurrent water. Reversed beating may be a general response to all unusual stimuli to the respiratory system. The pattern of water flow into and through the gill chambers was determined. The relative volume of water entering each incurrent aperture between the legs was calculated and indicated that approximately equal volumes of water entered each aperture. It is concluded that forward pumping adequately irrigates all gill surfaces.
Distribution of Oxygen Tension in the Blood and Water Along the Secondary Lamella of the Icefish Gill
Authors: Hughes G. M.
Published: April 2021

In spite of the extensive studies that have been made in recent years on the structure and function of gills, especially in fish, little is known about the O2 tensions at different points along the exchange surface.
Temperature-Dependence of Permeability to Water and To Sodium of the Gill Epithelium of the Eel Anguilla Anguilla
Authors: Motais R. , Isaia J.
Published: April 2021

The temperature dependence of diffusional permeability to water was studied in freshwater-adapted and seawater-adapted eels. The pattern of temperature acclimation is discussed. The ratio of water permeability to sodium permeability is approximately 3 at 25 °C, but falls to 1 at 5 °C. This drop is mainly due to a diminution of the water permeability, the temperature coefficients being much higher for water than for sodium. The relatively independent variations of water and sodium permeabilities in the seawater-adapted fish probably indicate a certain dissociation between water movements and salt movements. In the freshwater-adapted eel the osmotic permeability is considerably higher than the diffusional permeability, which supports the previously advanced hypothesis concerning the presence of water-filled channels in the branchial epithelium. In the seawater-adapted eel the osmotic permeability is lower than the diffusional permeability, this difference being greater the lower the temperature. This surprising result must signify either that the osmotic pressure difference between blood and sea water does not represent the true osmotic gradient across the membrane, or that a reabsorption of water linked with a movement of solutes occurs in a specialized region of the gill.
A System of Electrically Coupled Small Cells in the Buccal Ganglia of the Pond Snail Planorbis Corneus
Authors: Berry Michael S.
Published: April 2021

The buccal ganglia of Planorbis contain a population of electrically coupled small cells. This has been studied, in preparations of isolated ganglia, by recording intracellularly from the cells two at a time. The population is usually silent but activity initiated in any one of its members tends to spread to the rest of the population in both ganglia. Failure of spread, or fatigue, gradually occurs on repetition. The group has the properties of a trigger system, initiating prolonged patterned activity in large numbers of neurones in the buccal ganglia. This may normally initiate feeding. In addition to central processes, both in the buccal ganglia and to the rest of the CNS, the system has peripheral axons in most of the buccal nerves. No synaptic input could be demonstrated. Action potentials in some of the cells increase greatly in duration with repetition. The resulting electrotonic EPSP’s, recorded in closely coupled trigger cells, correspondingly increase in size. The possible integrative significance of this is discussed, especially its effect in offsetting fatigue. In some preparations spontaneous bursting occurred in trigger cells and this elicited burst activity in large neurones, including motoneurones. The system may have an intrinsic pacemaker.
Cardiovascular and Respiratory Responses of Ducks to Progressive Hypocapnic Hypoxia
Authors: Jones David R. , Holeton George F.
Published: April 2021

Cardiac ouput, ventilatory minute volume and gaseous exchange at both tissues and lungs have been recorded in restrained unanaesthetized ducks exposed to simulated high altitudes. A comparison between two species of duck showed that despite a significantly lower heart rate in resting Muscovy ducks, cardiac output, on a weight basis, was the same as in White Pekin ducks. Respiratory frequency and tidal volumes differed in the two species although their minute volumes were in the same range. Ducks responded to reduction in oxygen tension of arterial blood by increases in cardiac output and ventilatory minute volume, both being significantly above control (normal at rest) when was in the range 54·5–63 mmHg. At all levels of hypoxia ducks were able to remove about 30% of the oxygen from the ventilated air. When was 38 mmHg the difference between arterial and venous blood had decreased by 20·5 mmHg from control and during hypoxia and arterial and venous pH rose. The rate of oxygen uptake fell markedly at the lowest level of hypoxia but remained constant so that R.Q. rose from 0·76 at control at 1·12 at of 38 mmHg. It is concluded that there are many basic similarities between the cardiovascular and respiratory responses of ducks and mammals when exposed to simulated high altitude.
Plasma Chloride and Sodium, and Chloride Space in the European Eel, Anguilla Anguilla L
Authors: Kirsch R.
Published: April 2021

New intra-vascular cannulation techniques are described, and also an extracorporal blood circuit containing an artificial heart and a counting cell. This makes possible a continuous study of the radioactivity of the blood. Plasma chloride concentration varies greatly in fresh-water eels despite good sodium regulation. The fresh-water to sea-water adaptation of eels is frequently accompanied by a temporary hypermineralization of the internal medium. This necessitates a high degree of cellular euryhalinity. The sea-water-adapted eel maintains strict homeostasis of its plasma chloride and sodium. The chloride distribution space decreases by 10% when eels are transferred from fresh water to sea water. The internal distribution of chloride is also modified and its fluxes between the ion compartments of the body are considerably increased.
Electrophysiological Analysis of Peripheral Neurones and Their Possible Role in the Local Reflexes of A Mollusc
Authors: Prior David J.
Published: April 2021

It has been shown by behavioural and electromyographic studies that local reflexes exist in the siphon wall musculature of Spisula. In contrast, the responsiveness of the siphon retractor muscles is centrally mediated. Clusters of neurone somata occur at the peripheral branching points of the siphonal nerves. Intracellular records obtained from these peripheral cluster cells indicate they are efferents to the siphon wall musculature. These cells receive synaptic input from a population of touch-sensitive afferents from the siphons and mantle. None of the peripheral cells from which records have been obtained provided any indication of being sensory in function. ‘Central delay’ measurements indicate the presence of only one synaptic transfer between the afferent input to a peripheral nerve junction and the output of cluster cells. The synaptic input to the cluster cells is shown to be subject to short-term modification (antifacilitation). This coupled with the direct evidence that the peripheral cells are functional neurones supports the possibility that molluscan peripheral neurones could mediate habituated responses.
A Neural Correlate of Behavioural Stimulus Intensity Discrimination in A Mollusc
Authors: Prior David J.
Published: April 2021

A behavioural sequence of Spisula is described that involves local reflexes, siphon retraction and valve adduction. The response to low-intensity tactile stimulation is locally mediated reflex activity of the siphon wall musculature. In response to medium-intensity stimulation, the siphon retractor muscles are activated along with local reflex activity. A neural correlate of this behavioural discrimination between low and medium stimulus intensities was obtained by simultaneous intracellular recordings from pairs of efferent neurones, one neurone type involved in local reflexes and one efferent tai the siphon retractor muscles. The peripherally located neurones of the siphon wall musculature (cluster cells) were found to have a lower spike threshold than the efferents to the siphon retractor muscles (pallial neurones). Several lines of evidence are presented that support the assumption that intra-somatic recordings from these neurones accurately reflect the activity of the synaptic region. The membrane electrical properties (i.e. input resistance, rheobasic current, threshold potential) of the two cell types were measured by passing current through single intrasomatic micro-electrodes. From these measurements it was found that the ‘critical firing level ’ of the cluster cells is significantly lower than that of the pallial neurones. By way of their differential sensitivities to synaptic input, the stimulusintensity discrimination could be mediated by cluster cells and pallial neurones directly.
Pulsatile Pressures in the Cranial Fluids of Heterodontus Portusjacksoni
Authors: Satchell G. H. , Rossiter G. T.
Published: April 2021

It has been shown in mammals (Hamilton, Woodbury & Harper, 1936, 1944) that dilation of the craniospinal blood vessels by the pressure pulses caused by straining and coughing is largely prevented by the direct communication of the raised intra-thoracic pressure to the cerebrospinal fluid (CSF). The pathways through which pressure is communicated include the loose areolar tissue around the spinal nerves, and the venous blood in the paravertebral plexuses which communicate with the large veins at the back of the thorax and abdomen. McIntosh, Estes & Warren (1956) have shown by means of myelograms that as the intrathoracic pressure rises, the spinal nerves move medially and the subarachnoid space narrows.

The Port Jackson shark, Heterodontus portusjacksoni exhibits spontaneous, rhythmic, and evoked coughing during which the pharynx is contracted and water is forced from the mouth and gill slits (Satchell & Maddalena, 1972). During an evoked cough water pressure in the pharynx may exceed 70 cm H2O ; this is more than thirty times that of normal respiration. Some preliminary observations indicated that here too the rise of pressure in the pharynx is communicated via the dorsal aorta to the craniospinal vessels, and, by some more direct route to the fluid surrounding the brain. The totally different anatomy of the respiratory system of a fish compared with that of a mammal suggested that the phenomenon required investigation.
Statocyst-Induced Eye Movements in the CrabScylla Serrata
Authors: Sandeman D. C. , Okajima A.
Published: April 2021

Irrigation of the statocysts of the crab Scylla serrata will activate the oculomotor neurones associated with eye movements. An investigation of the central mechanism of statocyst-induced nystagmus has been started with the description of the statocyst canals and a characterization of the sensory input from the hair receptors in the canals. The canals are shaped like two toroids joined at approximately right angles to one another. Direct observation of isolated statoliths and glass models of them shows that when they are rotated, fluid moves around the circumference of the statocyst canals and displaces the hair receptors protruding into them. The direction of displacement of the different groups of receptors in both statocysts is related to the axes of rotation and provides a unique output for rotation about each axis. Electrical recordings from the three types of receptor hairs show that the thread hairs are most probably the receptors responsible for detection of rotation about the vertical axis. The free hook hairs are sensitive enough to detect rotation about the horizontal axes. The statolith hairs are sensitive to maintained changes of position.
Osmotic and Ionic Regulation in A Terrestrial Snail, Pomatias Elegans (Gastropoda, Prosobranchia) With A Note on Some Tropical Pomatiasidae
Authors: Rumsey T. J.
Published: April 2021

The mechanisms of ionic regulation in terrestrial snails of the subclass Pulmonata have stimulated interest for some time (Duval, 1930; Fischer, 1931; Arvanitaki & Cardot, 1932; Pusswald, 1948; Vorwohl, 1961; Burton, 1966, 1968a, b, 1971); but relatively little work has been done on the terrestrial Prosobranchia. The latter have colonized land either via fresh water (Fam. Cyclophoridae) or by migration from the intertidal zone (Fam. Pomatiasidae). This study involves the latter group, concentrating on the British species Pomatias elegans (Müller).

The Pomatiasidae are restricted to calcareous soils (Kilian, 1951; Avens, 1964; C. Little, personal communication) and P. elegans is only found in damp environments (Kilian, 1951), never being active below a R.H. of 95 % (Meyer, 1925). From the restricted distribution of pomatiasids (Kerney, 1968; Rumsey, 1971) it would be expected that adaptation to the terrestrial habitat is minimal, and that this will be partly reflected in their homeostatic mechanisms.
Properties of the Optokinetic Motor Fibres in the Rock Lobster: Build-Up, Flipback, Afterdischarge and Memory, Shown by Their Firing Patterns
Authors: York B. , Wiersma C. A. G. , Yanagisawa K.
Published: April 2021

The properties of sets of motor fibres responding to both clockwise and anticlockwise rotation have been studied in the oculomotor nerve of the rock lobster. There are probably three, but perhaps four, units in each set. None of these fibres has statocyst input, but there is weak input onto the tonio fibres from the antennal joints such that the eye turns in the direction toward which e antenna points. Many preparations show bilateral visual input onto all fibres but the degree of coupling between the eyes is very variable, and at times can be nearly totally absent. Depending on the speed of rotation the fibres show a gradual build-up in frequency, during rotation in the preferred direction, interrupted by flipbacks. During the fast stage of the resulting nystagmic movements all agonistic fibres can be completely inhibited and all antagonistic ones can be activated, usually for a period of about 0·5 sec. Fibre activity is demonstrated which appears to underlie an ‘optokinetic memory’ of contrasting target position in the visual field. It consists of (a) very prolonged afterdischarges for a stationary striped pattern (b) resumption of discharges at an appropriate frequency after dark periods up to 2 min, and (c) adjustment of such frequencies to changes in stripe position during the dark period. The fibres show habituation to repeated stripe movement but the response can be dishabituated by passive rotation of the animal. The largest visual responses were obtained to intermediate speeds of stripe rotation (about 2°/sec).
The Ionic Basis of Axonal Conduction in the Central Nervous System of Viviparus Contectus (Millet) (Gastropoda: Prosobranchia)
Authors: Sattelle D. B.
Published: April 2021

The compound action potential recorded from the pleural-supraintestinal connective of Viviparus contectus consists of a large, slow component with an average conduction velocity of about 0·02 m/sec (at 23 °C) and a faster component with a conduction velocity of 0·10 m/sec (at 23 °C) for the fastest fibres. Both fast and slow action potentials are rapidly abolished by the substitution of tris chloride and choline chloride for the sodium salts of normal Ringer. Tetrodotoxin, applied at 10−5 M rapidly abolishes action potentials in all fibres. It is, therefore, concluded that a largely sodium-dependent mechanism of spike generation operates in all axons of the connective. Lithium ions effectively substitute for sodium ions in maintaining the fast action potentials for extended periods, whereas tetraethylammonium ions do not. When the calcium chloride of normal Ringer is replaced by sucrose, magnesium chloride or barium chloride, conduction of fast action potentials is maintained. A small increase in the sensitivity of all axons to tetrodotoxin is observed in calcium-free Ringer ; a slight reduction in the spike amplitude of fast action potentials follows the application of manganous ions at 5 mM/1 in normal Ringer. It is concluded that any possible contribution of calcium to the generation of the action current of the fast action potential is very small compared to that of sodium. All axons of the connective function for extended periods in sodium-free (dextran) Ringer. Under these conditions, tetrodotoxin blocks conduction in all fibres at concentrations of 10−6 M, suggesting that function in dextran Ringer is maintained by a sodium-dependent mechanism.
The Osmoregulatory System of the Amoeba, Acanthamoeba Castellanii
Authors: Pal R. A.
Published: April 2021

It is estimated that Acanthamoeba castellanii eliminates a volume of water equal to its body volume in about 15–30 min. About 7% of the vacuolar discharge enters the body by means other than osmosis through the surface membrane. Food vacuoles fusing with the contractile vacuole do not significantly affect the rate of output. Vacuolar output declines with the age of culture so that during the stationary phase of growth it is about half of that during early log phase of growth. The rate of output of the contractile vacuole decreases with an increase of concentration of a non-penetrating solute in the external medium and shows a rectilinear relationship up to 0·07 M concentration. A low residual output after 0·07 M may be due to food vacuoles and pinocytic vacuoles. On the basis of vacuolar output the excess internal osmotic pressure and permeability constant of water has been estimated as 0·07 M non-electrolyte and 0·04 μm min−1 atm. −1 respectively. On the basis of vacuolar behaviour it is concluded that the relative permeabilities of the plasma membrane to different solutes follows this order: methyl alcohol > ethylene glycol > urea > glycerol. On certain assumptions the permeability of the plasma membrane to ethylene glycol has been estimated provisionally as 0·107 × 10−16 mol/sec//im2/mol/l. Vacuolar behaviour suggests that sodium chloride, sodium nitrate, sodium sulphate and potassium chloride, but not magnesium chloride and calcium chloride, pass into the cell freely. Growth of populations of A. castellanii is almost normal in polyethylene glycol 600 up to 0·07 M concentration but in higher concentrations it is low. There are some indications of an increase in volume of A. castellanii in cultures of polyethylene glycol 600 up to 0·07 M concentration, but not in higher concentrations. For amoebae cultured in media containing polyethylene glycol 600 the rate of output of the contractile vacuole declines sharply with an increase of polyethylene glycol 600 up to 0·07 M concentration and then more gradually.
Inhibition of Spontaneous Lateral-Line Activity by Efferent Nerve Stimulation
Authors: Russell I. J. , Roberts B. L.
Published: April 2021

Efferent nerve fibres innervating the lateral-line sense organs of the dogfish Scyliorhinus were stimulated with trains of stimuli while spontaneous afferent activity was monitored. Significant changes in spontaneous impulse frequency could be produced when the efferent nerves were stimulated by trains of pulses at frequencies between 20–100 sec−1; lower stimulus frequencies had no visible effect. The impulse frequency decreased or was totally inhibited during the stimulus period and for 150–200 msec following it. The inhibitory effect was very variable and declined with repetitive stimulation. Stimulation of the efferent nerves to inactive afferent units was followed after 500 msec by a brief low-frequency discharge.
The Locomotor Activity Rhythm of Talitrus Saltator (Montagu) (Crustacea, Amphipoda)
Authors: Bregazzi P. K. , Naylor E.
Published: April 2021

Talitrus saltator possesses a clear-cut locomotor activity rhythm, largely under the control of a persistent endogenous timing mechanism of circadian frequency. In dim red illumination the period of the rhythm is somewhat greater than 24 b; in continuous white fight it is less than 24 h, provided that the animals are unable to avoid the light by burrowing. The rhythm is synchronized by light/dark fluctuations, and the animal is active during the dark period. The timing mechanism is temporarily advanced by increases in temperature, but otherwise it possesses a large measure of temperature independence within the normal environmental range. There is some evidence that, in groups, the animals influence one another and so reduce the rate of drift of the activity rhythm in constant conditions. The adaptive significance of the endogenous timing mechanism of Talitrus is discussed.
The Relationship between Cardiac and Respiratory Rhythms in the Dogfish, Scyliorhinus Canicula L
Authors: Hughes G. M.
Published: April 2021

Recordings were made over long periods of the ECG and pressure changes in the orobranchial (OB) cavity of unanaesthetized dogfish, kept in a closed circulation of aerated and temperature controlled sea water. Variations in cardiac frequency (11–64/min) and in ventilatory frequency (22–80/min) were observed between individuals of similar body size. Similar variations were observed in non-experimental fish kept in holding tanks. Analysis of tape-recordings using a Biomac computer was made for interval histograms and showed a greater variability of the ECG interval than of the OB pressure, but not at all times. The relationship between the two rhythms was further investigated using event correlograms showing the position of the ECG in an averaged ventilation cycle, which was divided into ten equal phases. In many fish the heart tended to beat in a particular phase, at least for short periods, but in some cases this was never observed. Given individuals also varied in the preferred phase. Complete synchrony was rarely observed, most fish showing evidence of varying degress of coupling between the rhythms. Analysis of this incomplete synchrony was carried out using polar co-ordinates which showed that in 60% of the recordings analysed there was some significant (1 % level) coupling between the rhythms. The phase angle varied considerably and was most commonly between o° and i8o°, i.e. during the first half of the cycle following the maximum positive OB pressure. It is concluded that further understanding of the relationship between these rhythms requires more detailed knowledge of flow patterns of blood and water across the secondary lamellae.
Cuticular Water Content and the Rate of Evaporation in the Terrestrial Isopod Porcellio Scaber Latr
Authors: Salminen Inga , Lindqvist Ossi V.
Published: April 2021

The free-water content of the cuticle of the isopod Porcellio scaber Latr. was measured after treatments which are known to affect the total rates of water loss from the animal. The animals were desiccated for various periods of time in dry air, after which the cuticular samples were taken. After antennectomy, which is known to reduce the evaporation rate in dry air, the water content of the cuticle remains steady but at a higher level than that of normal animals. The mean cuticular water contents 24 h after operation were 54·0 ± 0·80% and 50·6 ±0·88% (P < 0·01) respectively for desiccated animals. The water content of the cuticle of non-desiccated animals was not altered by this treatment; the differences show up only after desiccation. Both hydration and removal of a pair of legs can result in an increased rate of evaporation; during desiccation the cuticular water content decreases with increasing desiccation. The slope of the regression curve for both hydrated and leg-amputated animals differs significantly from both the zero slope as well as from the control curve. A tentative model for the water permeability characteristics of the cuticle of Porcellio is presented to explain the above data.
Electrophysiology of the Heart of An Isopod Crustacean: Porcellio Dilatatus
Authors: Delaleu J. C. , Blondeau A. , Holley A.
Published: April 2021

The effects of various ions and chemicals were tested on the resting or active membrane of the heart of the wood-louse Porcellio dilatatus. The curve relating the resting membrane potential to log [K+]0 was found to correspond with the theoretical curve expected from the Nernst equation at higher concentrations only. Excess K+ decreased both amplitude and rate of rise of the response while the rate of decline was increased. In K+-deficient solutions the duration of the plateau phase was at first increased, then depressed. The addition of K+ to a bathing medium deprived for several minutes of this ion caused a large increase in the membrane potential and in the response height. The way in which the membrane was seen to react was tentatively attributed to an electrogenic active pumping mechanism. In Na+-deficient solutions, the rate of rise and the height of the response were reduced while the resting membrane potential was decreased. Ca2+-deficient solutions depolarized the membrane and decreased both amplitude and duration of the response. Cessation of activity occurred in Ca2+-free solution. In excess calcium the membrane was hyperpolarized. The rhythm and the rate of rising were decreased and the plateau phase depressed. TTX blocked the heart activity, probably by acting upon the heart ganglion. Mn2+ depressed especially the humped plateau (when present) of the spontaneous responses. TEA, caffeine and procaine transformed spontaneous activity of weak amplitude into large and complex overshooting responses. In TEA solutions, several stable levels of polarization were observed. Contrary to what occurred in the normal solution, depolarizing current pulses could trigger large all-or-none action potentials when TEA was present. The TEA-induced regenerative response was analysed with the help of an intracellular stimulating current when [Na+]0 and [Ca2+]0 were varied. Additional data were obtained by applying TTX, Mn2+ or GABA. From the results, both Ca2+ and Na+ were thought to be involved in the ionic currents underlying spiketype activity. The spike-generating effect of TEA has been attributed to its property of increasing the membrane resistance and of allowing the ionic conductances which generate the weakly active component of the normal response, the plateau, but not the initial upstroke, to be amplified regeneratively. The large spikes elicited by TEA were found relatively less effective than weak sustained depolarization in inducing strong contractions. The functional significance of the data was tentatively interpreted by comparison with the properties of the heart of Limulus, Crustacea and vertebrates.
Photosensitive Neurones in the Marine Pulmonate Mollusc Onchidium Verruculatum
Authors: Hisano Nozomu , Tateda Hideki , Kuwabara Masutaro
Published: April 2021

Giant photosensitive neurones were found in the sub-and supra-oesophageal ganglia of the marine pulmonate mollusc Onchidium verruculatum. Some were photo-excitative neurones; spikes appeared or their frequency increased in response to light stimuli. The others were photo-inhibitive neurones in which disappearance of spikes or decrease in their frequency was noted in response to light. Photosensitive neurones were distinguished according to whether or not they were ‘primary’ neurones, i.e. responded directly to a minute light spot. Three primary neurones and three secondary neurones were detected among the photo-excitative neurones. There were four primary photo-inhibitive neurones. It was not determined whether a neurone was primary or not. An inverse effect of light on one of the primary photo-excitative neurones, ES-I, occasionally occurred after illumination of long duration. A light stimulus which had previously excited the neurone, inhibited subsequent spontaneous discharge. The inhibitory effect of light on one of the primary photo-inhibitive neurones was overcome by some excitatory process during illumination of long duration or after repeated light stimuli.
The Effect of Increased Ambient CO2 On Arterial CO2 Tension, CO2 Content and pH in Rainbow Trout
Authors: Cameron James N. , Randall David J.
Published: April 2021

The effect of exposure of rainbow trout to high and low levels of environmental (water) CO2 tension on blood CO2 and pH was studied. An increase in environmental CO2 caused a rise in the arterial CO2 tension , but the blood-to-water gradient (P1-Pa) remained about the same. Changes in arterial pH were small - about one-third of what would be predicted from the change in if plasma bicarbonate remained constant. There was a corresponding increase in the total CO2 content of the blood which involved an upward shift of the CO2 dissociation curve, and readjustment of the buffering to maintain pH. The results are consistent with the hypothesis that blood CO2 and pH levels are regulated via a chloride-bicarbonate exchange mechanism, rather than by ventilation and diffusive washout of gaseous CO2.
Changes in Chemoreceptor Sensilla on the Maxillary Palps of Locusta Migratoria in Relation to Feeding
Authors: Bernays E. A. , Blaney W. M. , Chapman R. F.
Published: April 2021

The electrical resistance across the tips of the maxillary palps of Locusta migratoria is high immediately after a feed, but falls to a steady level in about 2 h after feeding. Only a small proportion of the individual sensilla on the domes of the palps respond to chemical stimulation immediately after feeding, but this proportion increases with the period of food deprivation. Gentle manipulation of the tips of non-responsive sensilla causes them to respond. It is suggested that the terminal pores of the sensilla can open and close and that the resistance across the tips of the palps varies inversely with the number of open sensilla. The possible significance of the changes is discussed.
On the Interactions Between Suctorial Adhesion, Gill Ventilation and Opercular Spine Erection In Xenocara Occidentalis*
Authors: Gradwell Norman
Published: April 2021

Except for brief swimming from one site of adhesion to another, the oral sucker of Xenocara is constantly used to anchor the fish to the substratum. During adhesion oral inhalation is by rhythmic water flow through special grooves in the sucker wall. Coarse particles entering with the respiratory water elicit a cough-like response which is associated with large positive pressures in the bucco-pharynx and opercular cavities, and with enhancement of suctorial adhesion. Stronger adhesion occurs when the fish responds to tactile stimulation, during which large negative pressures are developed throughout the respiratory system and the opercular spines are thrust outward. In all responses separation of suctorial and respiratory function is facilitated by the action of a muscular oral valve. Precise co-ordination between the inlet valves of the maxillary barbels and the oral and opercular valves is important for efficiency of the suction and force pumps before the gills and the opercular suction pump behind them.
Physiology of Insect Rhythms
Authors: Truman J. W.
Published: April 2021

In insects the development of a rigid exoskeleton requires that for growth and metamorphosis to occur a new cuticle must be periodically formed and the old one cast off. This process (the moult) is initiated with the release of the prothoracicotropic hormone (PTTH) from the brain. Then follows the secretion of a second hormone, ecdysone, by the prothoracic glands, the apolysis of the epidermis from the cuticle, the secretion of a new cuticle, and, finally, the shedding or ecdysis of the old cuticle. The type of cuticle formed is regulated by a third hormone, the juvenile hormone (JH), produced by the corpora allata (see Wigglesworth (1971) and Wyatt (1972) for current reviews of the hormonal control of moulting). Recently, a study of the eclosion of adult silkmoths revealed that the last step in the moulting process is also under endocrine control (Truman & Riddiford, 1970). In this case a neurosecretory hormone from the brain acts on the nervous system to trigger the behaviour involved in emergence (Truman, 1971 ; Truman & Sokolove, 1972).
Potassium Movements in A Central Nervous Ganglion of Limnaea Stagnalis (L.) (Gastropoda : Pulmonata)
Authors: Sattelle D. B.
Published: April 2021

Resting potentials and action potentials recorded from in situ, intact and desheathed giant neurones of the right parietal ganglion of Limnaea stagnalis are of similar magnitude. Ganglionic potential profiles reveal the absence of a sheath potential. It is concluded that the extra-neuronal fluid has a similar ionic composition to the blood (bathing medium). A 34 mV decade potassium slope is obtained for both intact and de-sheathed neurones. Depolarization of the neuronal membrane takes place rapidly in intact preparations, and the de-sheathing procedure significantly increases the rate of depolarization. A reduction in temperature from 23 to 8 °C only slightly prolongs the time-course of depolarization of an intact neurone. When the concentration of potassium in the fluid bathing the surface of an intact ganglion is elevated, the concentration of this cation at the neuronal surface changes exponentially with time. It is suggested therefore that diffusion along the extracellular channels is the mechanism and pathway for the movement of potassium ions through the right parietal ganglion of Limnaea stagnalis.
Humoral Regulation of the Cerebral Neurosecretory System of Rhodnius Prolixus (Stal.) During Growth And Moulting
Authors: Steel C. G. H.
Published: April 2021

In normal fifth instar Rhodnius the cytological changes occurring in the medial neurosecretory cells (MNC) of the brain are very different before and after the ‘critical period’ for decapitation. When a decapitated insect which has reached the ‘critical period’ (8 days after feeding) is joined in parabiosis to an insect with an intact cerebral endocrine system and which has not yet reached the ‘critical period’ (1 day after feeding) the MNC of the younger insect are induced to switch over from their normal sequence of cytological changes to those characteristic of the older insect. The induced changes do not occur in normal insects of the same age or in insects joined in parabiosis to others of the same age. The nature of the changes indicates that release of stainable neurosecretory material is inhibited and its synthesis stimulated by the older insect. It is inferred that the haemolymph of insects which have reached the ‘critical period’ contains a factor which induces in the MNC an inhibition of release and a stimulation of synthesis. These are the events which occur in the MNC of normal insects at the critical period. Considerable circumstantial evidence suggests that the factor is ecdysone. It may act either directly on the brain or on the corpus allatum. Its contribution to a feedback regulation of the endocrine system controlling growth and moulting is discussed.
Phototaxis in Limulus Under Natural Conditions: Evidence For Reception of Near-Ultraviolet Light in the Median Dorsal Ocellus
Authors: Lall Abner B. , Chapman Robert M.
Published: April 2021

Phototactic behaviour in Limulus mediated by lateral eye and dorsal ocellus was studied under full-spectrum and restricted-spectrum (near-u.v. and visible light) sunlight on a beach. All eyes (lateral eyes, dorsal ocelli) were occluded excepting one, which mediated the response. It was found that either a lateral eye or a dorsal ocellus alone could mediate positive phototaxis in adult Limulus under full-spectrum sunlight. When the sunlight stimulating the dorsal ocellus was filtered into restricted wavelengths, the near-u.v., but not the visible light, elicited positive phototaxis.
Na+/NH4+, Na+/H+ Exchanges and NH3 Movement Across the Gill of Carassius Auratus
Authors: Maetz J.
Published: April 2021

Sodium uptake from the external medium in the absence of permeant co-ion occurs in most freshwater animals. Exchange of Na+ for an endogenous cation is necessary to maintain the electroneutrality of the external and internal media.