Showing papers in "The Journal of Experimental Biology in 1970"

Respiration and Osmoregulation in Rainbow Trout with Gills Damaged by Zinc Sulphate

Abstract: 1. Damage to the gill epithelium occurs when hatched fish are killed rapidly by solutions of zinc sulphate. 2. The rate of routine oxygen uptake by lightly sedated, quiet, rainbow trout did not alter on exposure to a rapidly toxic solution of zinc sulphate. However, oxygen utilization decreased seven-fold, gill ventilation volume increased six-fold, heart rate was halved, coughing rate increased 18-fold and the Po2 of dorsal aortic blood declined. 3. Unsedated trout usually struggled on exposure to zinc. The survival time of struggling fish was reduced and oxygen uptake increased, but other physiological changes were similar to those in quiet fish. 4. The respiratory changes in poisoned trout were generally similar to changes observed earlier in the same fish under hypoxia. 5. The osmotic concentration and the concentrations of sodium, potassium, calcium, magnesium and zinc in blood were largely unaffected by immobilization in zinc sulphate solution. Trout survived a four-fold increase in zinc concentration in the blood by injection. 6. The results suggest that epithelial damage decreased the permeability of the gills to oxygen, and did not increase their permeability to cations. Zinc was not a rapid internal poison. Death was probably caused by tissue hypoxia, when maximum gill ventilation was no longer sufficient to supply the oxygen needs of the fish.

Discharge patterns of coxal levator and depressor motoneurones of the cockroach, periplaneta americana

Abstract: 1. Observation of movements of the metathoracic legs of the cockroach before and after section of peripheral nerves allowed identification of muscles involved in flexion and extension of the femur. 2. Extracellular recordings from the nerves to these coxal muscles show that during rhythmic leg movements bursts of activity in a number of levator motor axons were strongly reciprocal and generally non-overlapping with those of a slow depressor motor axon. 3. These reciprocal patterns persisted after removal of all sensory input from the legs. 4. The durations of levator bursts were relatively constant compared to those of the depressor, corresponding to the behavioural observations on leg protraction time. The pattern was asymmetric: levator bursts could be generated without depressor activity, but never the reverse. 5. No evidence was found for inhibitory collateral pathways between antagonist motoneurones. 6. It is proposed that levator motoneurones are driven by a group of bursting interneurones which simultaneously inhibit the ongoing depressor activity.

Aerodynamics of Gliding Flight in a Falcon and Other Birds

Abstract: 1. A live laggar falcon ( Falco jugger ) glided in a wind tunnel at speeds between 6.6 and 15.9 m./sec. The bird had a maximum lift to drag ratio ( L / D ) of 10 at a speed of 12.5 m./sec. As the falcon increased its air speed at a given glide angle, it reduced its wing span, wing area and lift coefficient. 2. A model aircraft with about the same wingspan as the falcon had a maximum L / D value of 10. 3. Published measurements of the aerodynamic characteristics of gliding birds are summarized by presenting them in a diagram showing air speed, sinking speed and L / D values. Data for a high-performance sailplane are included. The soaring birds had maximum L / D values near 10, or about one quarter that of the sailplane. The birds glided more slowly than the sailplane and had about the same sinking speed. 4. The ‘equivalent parasite area’ method used by aircraft designers to estimate parasite drag was modified for use with gliding birds, and empirical data are presented to provide a means of predicting the gliding performance of a bird in the absence of wind-tunnel tests. 5. The birds in this study had conventional values for parasite drag. Technical errors seem responsible for published claims of unusually low parasite drag values in a vulture. 6. The falcon adjusted its wing span in flight to achieve nearly the maximum possible L / D value over its range of gliding speeds. 7. The maximum terminal speed of the falcon in a vertical dive is estimated to be 100 m./sec.

Body weight and the energetics of temperature regulation.

Abstract: 1. The interactions of basal rate of metabolism, thermal conductance, body temperature, lower limit of thermoneutrality, and body weight in mammals are compatible with Newton9s law of cooling. 2. A small body weight will normally reduce the level and preciseness of body temperature, but a high basal rate of metabolism or a low thermal conductance may compensate for a small size and permit a high, precise temperature to be maintained. 3. The parameters of energetics that fix the level and preciseness of body temperature in mammals are ultimately correlated in turn with the environmental parameters of climate and food habits. 4. Birds generally have higher temperatures than mammals because the basal rates of metabolism are higher and the conductances lower in birds than in mammals of the same weight.

The Mechanism and Efficiency of Sound Production in Mole Crickets

Abstract: 1. Sound production in the mole crickets Gryllotalpa vineae and G. gryllotalpa is compared with that in Gryllus campestris . 2. In all species action of the plectrum of the left forewing on the file or pars stridens of the right wing causes the harp areas of both wings to vibrate in phase with each other. As the lateral and dorsal fields of the wing are coupled flexibly, the dorsal field resonates freely. 3. The available muscular power of G. vineae is about 3.5 mW., of G. gryllotalpa about 1 mW., and of Gryllus about 1.2 mW. The mesothoracic musculature of Gryllotalpa is fairly similar to that of Gryllus . 4. The calling song of G. vineae has a fundamental frequency of 3.5 kHz, a pulse length of 8 msec. and a pulse interval of 14 msec. at 16° C. The song is very pure with a second harmonic of -26 dB. Simulations of the song made with modulated oscillators are of similar purity; the song can be regarded as a modulated pure note. 5. The sound distribution has been measured, and from the area of an isobar plot and calculation of the mean power of each pulse, the total mean sound power output is 1.2 mW. and the peak power 3 mW. The efficiency of conversion of muscular to acoustic power is about 35%. 6. G. vineae builds a double-mouthed horn-shaped burrow for singing. This contains a bulb which probably tunes the horn to act as a resistive load to the vibrating wings. The double mouths act as a line source with directional properties which concentrate the sound in a disk above the length of the burrow. 7. The probable advantage of a directed sound output in attracting mates is considered; the disk-shaped pattern will be better than a hemispherical pattern of similar power. 8. G. gryllotalpa also builds a horn, but this is larger than that of G. vineae and the song frequency is far lower, at 1.6 kHz. Although the sound power is far lower, about 2.5x10 -5 W., the horn appears to act as a resistive load to the wings. 9. Gryllus produces only about 6x10 -5 W. at 30° C. This is attributed to the small size and hence low radiation resistance of the wings. 10. Estimates are made of inertial losses that occur in sound production and these are shown to account for a substantial part of the mechanical power in the systems of both G. vineae and Gryllus .

The Metabolic Cost of Swimming in Ducks

Abstract: 1. The metabolic cost of swimming was studied in mallard ducks ( Anas platyrhynchos ) which had been trained to swim steadily in a variable-speed water channel. 2. At speeds of from 0.35 to 0.50 m/sec the oxygen consumption remained relatively constant at approximately 2.2 times the resting level. At speeds of 0.55 m/sec and higher the oxygen consumption increased rapidly and reached 4.1 times resting at the maximum sustainable speed of 0.70 m/sec. 3. The maximum sustainable swimming speed of the ducks coincided with the limit predicted from hydrodynamic considerations of the water resistance of a displacement-hulled ship of the same hull length as a duck (0.33 m). 4. The cost of transport (metabolic rate/speed) reached a minimum of 5.77 kcal/kg km at a swimming speed of 0.50 m/sec. Ducks swimming freely on a pond were observed to swim at the speed calculated in experimental trials to give minimum cost of transport. 5. Drag measurements made with model ducks indicated a maximum overall efficiency (power output/power input) for the swimming ducks of about 5%. Ships typically have maximum efficiencies of 20-30%. Because of the difficulty in delimiting the cost of swimming activity alone from the other bodily functions of the duck, overall efficiency may present an incorrect description of the swimming performance of the duck relative to that of a ship. An hydrodynamic parameter such as speed/length ratio [speed/(hull length)½] whereby a duck excels conventional ships may present a more appropriate comparison.

Aspects of the Physiology of Terrestrial Life in Amphibious Fishes: II. The Chilean Clingfish, Sicyases Sanguineus

Abstract: 1. A study has been made of major aspects of the physiological adaptations for terrestrial life possessed by the amphibious clingfish, Sicyases sanguineus , on the coast of central Chile. 2. These fish can survive for more than 1½ days out of water, if not exposed to severe dehydration or thermal stresses. Rates of evaporative water loss while out of water are low. Upper lethal temperatures are also low, reflecting the uniformly cool water temperatures of their environment. In nature the fish rarely leave areas in which they are frequently washed over by waves. 3. These fish demonstrate an unusual combination of metabolic and cardiovascular adjustments to emersion. Metabolic rates (oxygen consumption) of small (1-5 g weight) fish are higher out of water than in water. Larger fish show a pattern of intermittent oxygen uptake when out of water. Heart rates respond to emersion (and associated cessation of breathing movements) in the pattern of the diving syndrome. Lactic acid concentrations in the blood gradually increase above control levels during the first few hours of emersion, then remain constant at about x 3 control level. There is no indication of peripheral vascular shutdown during emersion. 4. Emersion produces a marked shift towards ureotelism in waste nitrogen production. There appears to be no systemic accumulation of ammonia during emersion. 5. The generality of the results, and also their physiological significance, are discussed.

Sodium regulation in the freshwater mollusc Limnaea stagnalis (L.) (Gastropoda: Pulmonata).

Abstract: 1. Sodium regulation in normal, sodium-depleted and blood-depleted snails has been investigated. 2. Limnaea stagnalis has a sodium uptake mechanism with a high affinity for sodium ions, near maximum influx occurring in external sodium concentrations of 1.5-2 mM-Na/l and half maximum influx at 0.25 mM-Na/l. 3. L. stagnalis can maintain sodium balance in media containing 0.025 mM-Na/l. Adaptation to this concentration is achieved mainly by an increased rate of sodium uptake and a fall of 37 % in blood sodium concentration, but also by a reduction of the sodium loss rate and a decrease in blood volume. 4. A loss of 23% of total body sodium is necessary to stimulate increased sodium uptake. This loss causes near maximal stimulation of the sodium uptake mechanism. 5. An experimentally induced reduction of blood volume in L. stagnalis increases sodium uptake to three times the normal level. 6. About 40% of sodium influx from artificial tap water containing 0.35 mM-Na/l into normal snails is due to an exchange component. Similar exchange components of sodium influx were also observed in sodium-depleted and blood-depleted snails in the same external sodium concentration.

Yaw-correcting postural changes in locusts*

Abstract: 1. Changes in the angle of the relative wind sensed by the facial wind receptors of a locust evoke fast rudder-like movements of the abdomen and legs whose magnitudes are proportional to the change of wind angle. 2. This system is sensitive to the angular velocity of the wind change. 3. Such wind changes also evoke rotations of the head about the long axis of the body. 4. The head rotation induces, through proprioception by the cervical hair receptors, slow, redundant rudder-like movements of abdomen and legs. 5. Control elements for the fast movements of abdomen and legs and for the head rotation appear not to be precisely co-ordinated and seem to include no proprioceptive ‘crosstalk’. 6. All these responses are evoked by wind-angle changes only if the insect is flying at the moment, suggesting that flight closes a neuronal switch. 7. Separate motor pathways seem to be employed for the abdomen's rudder-like response to wind-angle change, head rotation and turn tendency. Supported by National Science Foundation Grant no. B9-0425R and funds from Cornell University's Division of Biological Sciences.

The role of 5-hydroxytryptamine and cyclic AMP in the control of fluid secretion by isolated salivary glands.

Abstract: 1. Isolated salivary glands of Calliphora have been used as a system on which to study the mode of action of a hormone. 2. Cyclic AMP, which is thought to mediate the action of many different hormones, can stimulate fluid secretion equally as well as 5-HT. 3. Methyl xanthines, which inhibit the hydrolysis of intracellular cyclic AMP by phosphodiesterase, can stimulate secretion and prolong recovery time after removal of 5-HT. 4. Methyl xanthines can sensitize salivary glands to both 5-HT and cyclic AMP. 5. Butyryl derivatives of cyclic AMP can stimulate secretion, but their effect is slower and lasts longer. 6. Certain amino acids and malate support fluid secretion more effectively than trehalose or glucose. 7. It is concluded that cyclic AMP plays an important role in the ability of 5-HT to control fluid secretion by salivary glands.

The control of water loss in desert tenebrionid beetles.

Abstract: 1. Total water loss in tenebrionid beetles was composed of transpiratory losses from the cuticle and spiracles, water associated with defaecation, and water from the release of defensive quinone droplets or oral fluids. 2. Freshly killed specimens of E. armata, C. muricata and C. verrucosa had higher transpiration rates over long and short exposures than did living animals of the same species. These results may reflect the cessation of active water retention by cuticular and spiracular regulation in dead animals. 3. Cuticular transpiration, although low in absolute rate, was a greater source of water loss than respiratory transpiration in E. armata, C. muricata and C. verrucosa at temperatures from 25 to 42.5 °C and at 0% R.H., suggesting that spiracular control of water loss was of considerable importance in maintaining water balance. 4. A marked increase in respiratory transpiration over previous low rates was observed at 40 °C for E. armata and at 42.5 °C for C. muricata and C. verrucosa , and indicated a temperature-induced breakdown in spiracular water regulation due to increased respiratory activities. In contrast, cuticular transpiration maintained a linear rate of increase over the temperature range investigated. 5. A direct relationship existed between oxygen consumption and estimated respiratory transpiration for E. armata from 25 to 40 °C and at 0% R.H. 6. Evidence for the presence of discontinous respiration and unidirectional tracheal air flow in E. armata was presented. 7. Cuticular transition temperatures were measured for E. armata (40 °C), C. muricata (47.5 °C), and C. verrucosa (50 °C) with results showing that the autumn species ( E. armata ) possessed a lower cuticular breakdown point than either of the two summer species. 8. Much of the success of tenebrionid beetles in desert habitats is due to the development of highly impermeable cuticles and well regulated spiracular control mechanisms for reducing the loss of body water.

The Effects of Prolactin and Divalent Ions on the Permeability to Water of Fundulus Kansae

Abstract: 1 Measurements have been made of the rate of exchange of tritiated water in both intact and hypophysectomized Fundulus kansae in a variety of media 2 Hypophysectomy reduces the rate of exchange in fresh water 3 Low doses (30 mu) of ovine prolactin stimulate water turnover in hypophysectomized fish in fresh water 4 The rate of exchange declines in both intact and hypophysectomized animals with increasing salinity 5 Experiments with synthetic solutions show that the decline in the rate of exchange in sea water and in higher salinities is due mainly to the effects of calcium ions 6 Fishes maintained in synthetic sea water containing a low concentration of calcium have both a higher rate of exchange of tritiated water and a higher drinking rate than fish in normal sea water

Responses of the respiratory pumps to hypoxia in the rainbow trout (Salmo gairdneri).

Abstract: 1. Unanaesthetized rainbow trout, when subjected to a lowered P o 2 of the inspired water, show an increase in amplitude of pressures recorded from the buccal and opercular cavities. Pressure amplitudes were commonly found to be 0.5 cm of water in resting trout and increased 4- or 5-fold as inspired P o 2 was reduced. Differential pressures across the gills also increased with hypoxia. 2. Typically the minute volume in a 400-600 g trout increased from about 0.2 to 0.6 l/kg/min when the inspired P o 2 was lowered from 150 to 80 mm Hg, but rose to 1-5l/kg/min at lower P o 2 . Increased minute volumes are mainly due to increases in stroke volume; respiratory frequency remains fairly constant at P o 2 9s above about 8o mm Hg. 3. The relation between differential pressure and minute volume is fairly linear over much of the range, but minute volume increases more rapidly than differential pressure. 4. Oxygen consumption of the non-swimming fish increases during hypoxia and is related to the increased ventilation and differential pressure across the gills. 5. Estimates of the oxygen cost of breathing were made from the increased oxygen consumption during hyperventilation. Comparison of these estimates with estimates of the work done, using the pressure and volume measurements, gave figures for the overall efficiency of the pumping mechanism of about 10%.

Fluorescence localization of monoamines in crab neurosecretory structures.

Abstract: 1. The pericardial organs and anterior ramifications (both neurohaemal structures) of six species of crabs have been examined as whole mounts by the histochemical method for monoamines based on formaldehyde-induced fluorescence. 2. A small number of specifically fluorescing axons (not more than six green and six yellow) innervate the pericardial organ; one of the green-fluorescent and one yellow-fluorescent axon branches and also innervates the anterior ramification. 3. All of the fluorescing axons enter via segmental nerves 1, 2 and 3 from the ventral ganglion. 4. One large, brilliant green-fluorescing axon, and the small green-fluorescing axon which branches to the AR, have been traced in Carcinus to cell bodies in the circumoesophageal connective ganglion. These cells may give rise to the entire population of green-fluorescing axons and terminals in the neurohaemal organs. 5. Each axon, throughout its course in the pericardial organ, supplies a dense array of varicosities (blebs) at surfaces which are directly exposed to the haemolymph. The anterior ramifications are also supplied with blebs. 6. Lack of fluorescence in controls not exposed to paraformaldehyde, reversible quenching of fluorescence by treatment with sodium borohydride, and depletion of the fluorescence by reserpinization of the crabs, all confirm that the fluorescence is specific and represents the intracellular localization of monoamines. 7. With the aid of data available elsewhere we conclude that there are distributed, in parallel with peptide-secreting axons and terminals in the pericardial organs and anterior ramifications, a group of dopamine-containing and a group of 5-hydroxytryptamine-containing axons and terminals.

Properties of action potentials from insect motor nerve fibres.

Abstract: 1. The properties of nerve action potentials in small insect motor nerves were studied using extracellular recording electrodes. 2. A length of nerve was lifted out of solution and recordings were made with respect to the solution either from an intact nerve (triphasic recording) or from near a cut end of the nerve (monophasic recording). 3. In a cockroach nerve, the number of spontaneously active fibres was small enough that corresponding nerve fibres could be identified in each preparation by their action potential amplitude and their pattern of activity. Under controlled conditions, the absolute amplitudes of either monophasic or triphasic records were reproducible and could be used to calculate fibre diameter. The calculations were confirmed from histological sections of the nerve. 4. Conduction velocity varied approximately as the 0.78 power of fibre diameter in a cockroach nerve and as 0.7 power of fibre diameter in a locust nerve. These values are considerably larger than the square root relation predicted if membrane properties are independent of fibre diameter. 5. Membrane properties probably vary with fibre diameter since the action potential duration increases dramatically for fibres below 5 µ in diameter. 6. For the cockroach nerve systematic structural differences between fibres of different sizes are also seen with the electron microscope and the relation of these to the functional differences is considered.

The Mechanics of Stridulation in Bush Crickets (Tettigonioidea, Orthoptera): I. The Tegminal Generator

Abstract: 1. A method has been devised by which the isolated tegmina of bush crickets can be actuated in such a manner as to simulate the insect9s natural song. 2. The actuator was used to make a detailed analysis of the mechanics of sound production, with particular reference to the emission of the more or less pure tone at 15 kHz., characteristic of Homorocoryphus nitidulus . 3. Results involving damping and cautery indicated that the area of the right tegmen responsible for the radiation of this sound was the mirror frame, the vein enclosing the classical mirror membrane. 4. Further experiments involving transduced sound and a probe microphone led to the construction of sound radiation maps of the right tegmen which supported the above view. 5. The cantilever hypothesis, involving the mirror frame with the axis of the vestigial file as the cantilever9s rotational axis, was considered in the light of the Homorocoryphus type. 6. The Homorocoryphus type differed from the Conocephalus type (on which the cantilever hypothesis was based) in that a simpler cantilever is formed in a line direct from the plectrum to the tip of the frame arm.

Geotaxis in motile micro-organisms

Abstract: In this paper it is shown that the variable-density orientation cannot completely account for geotaxis in ciliates such as Paramecium, and it is suggested that the principal cause is a hydrodynamic interaction between the organisms and the medium, the magnitude of which is determined by the size and shape of the organism. Many of the motile protozoa, for example, are characteristically wider at the rear than at the front; because larger objects tend to fall more rapidly in a viscous fluid, the rear tends to sink below the front, thus producing an upward orientation. The nature of the hydrodynamic interaction is investigated using small-scale models falling through glycerol, and the results are compared with similar experiments on immobilized paramecia. A general theory is developed for describing the motion of these organisms under gravity, and the predictions of the theory are compared with measurements on suspensions of paramecia in long, vertical columns. The observations that low temperatures (Moore, 1903) and bright sunlight (Fox, 1925) induce positive geotaxis in Paramecium are interpreted in the light of the theory. Finally, the possible importance of geotaxis in other motile micro-organisms such as bacteria and spermatozoa is considered.

Wettability and Phylogenetic Development of Feather Structure in Water Birds

Abstract: 1. The water repellency of feathers is determined mainly, but not exclusively, by a structural parameter which can be expressed in terms of diameter and spacing of the barbs and barbules. 2. Effective waterproofing properties result from the optimal balance of structural parameter and resistance to water penetration. 3. Comparison of the structural parameters for water birds with the geological time interval of their earliest fossil record shows a phylogenetic tendency toward optimizing waterprooftng properties with the course of time. 4. Several behavioural patterns are discussed which may have evolved under the selective pressure of the quality of water repellency and resistance to water penetration.

Giant Fibre and Small Fibre Pathways Involved in the Evasive Response of the Cockroach, Periplaneta Americana

Abstract: 1. Giant fibres were found not to activate leg motoneurones during evasion. 2. A pathway of small axons having a conduction velocity of 1.5-35 m./sec. was found to govern leg activation during escape. 3. This pathway remains functional after giant-fibre degeneration after the giant axons have been severed from their somata. 4. Movements of the antennae were found to be activated by the giant fibres simultaneously or slightly earlier than movements of the legs. 5. It is suggested that a general alarm system is activated by the giant fibres concomitantly with activation of the leg motoneurones by a slower conducting pathway.

Respiration in an Air-Breathing Fish, the Climbing Perch Anabas Testudineus Bloch : I. Oxygen Uptake and Carbon Dioxide Release into Air and Water

Abstract: 1. Respiration of the climbing perch Anabas has been studied under five different experimental conditions. ( a ) The mean O2 consumption of a fish allowed free access to air, is about 113 c.c./kg/h at 25°C. The fish obtain nearly equal amounts of oxygen through the gills and through the accessory organs. ( b ) The overall O2 consumption from water of a fish allowed free access to nitrogen is nearly the same as during normal respiration from water with access to air. ( c ) The O2 consumption is reduced when the fish is out of water and obtains all its oxygen from air. ( d ) The O2 consumption from air increases considerably when the fish is maintained in de-oxygenated water and depends upon surfacing for its oxygen supply. ( e ) The O2 consumption of a fish kept in aerated water and prevented from surfacing remains at a minimum level relative to the other four conditions. 2. Much more carbon dioxide is released through the gills than through the accessory organs (10:1) when the fish respires from aerated water with access to air. The accessory organs are much more important for O2 uptake. 3. The respiratory quotient is approximately 1 when the fish is in aerated water, with or without access to air, but is only 0.7 when the fish is out of water. 4. Anabas can live out of water for 6-10 h if protected from dehydration. It continues to breathe quietly in air-saturated water using its gills alone for shorter periods (6-8 h) when denied free access to air.

Water relations of the desert scorpion, Hadrurus arizonensis.

Abstract: 1. Total water-loss rates for Hadrurus arizonensis (0.028% wt/h at 30 °C in dry air) are comparable to rates for Old World species and are well below rates for other desert arthropods under similar conditions. 2. Cuticular and respiratory transpiration constitute the two major avenues of water loss, cuticular water loss predominating at temperatures up to approximately 38 °C and respiratory transpiration predominating at temperatures above 40 °C. 3. The cuticular transpiration/temperature curve exhibits a two-plateau configuration with abrupt increases in cuticular permeability occurring between 35 and 40 °C and between 65 and 70 °C 4. Cuticular water-loss values in dead scorpions exceed those of total water loss in living scorpions. The increased cuticular permeability after death is interpreted as evidence for the existence of an active cuticular water-retaining mechanism. 5. Water-loss rates are significantly reduced at lower saturation deficits; however, scorpions are unable to absorb significant quantities of water from near-saturated atmospheres or moist substrates, regardless of their hydration state. 6. The importance of water conserving versus water regaining mechanisms are discussed in relation to the total adaptations of these animals to hot, dry environments.

A quantitative study of potassium movements in the central nervous system of Periplaneta americana.

Abstract: 1. Using the electrical response of giant axons in the isolated abdominal nerve cord of the cockroach, Periplaneta americana, as an indication of the ionic composition of the fluid bathing their surfaces, it has been shown that the movement of potassium ions from the bathing medium to the extra-axonal fluid, following an increase in the external concentration of this cation, involves an appreciable degree of restriction. 2. This effect is associated with an extracellular diffusion potential, which appears to result from the more rapid penetration of potassium relative to the outward diffusion of sodium ions from the extracellular system. 3. It is suggested that the restriction of intercellular diffusion may occur in the region containing tight junctions and separate desmosomes at the inner end of the intercellular clefts which traverse the perineurium. 4. If the connectives are stretched during mounting, a more rapid depolarization of the giant axons is observed. Comparison of the calculated and the experimentally observed half-times for diffusion of potassium ions to the axon surface indicates that in these preparations the rate of movement of inorganic ions from the external medium is largely determined by the extended intercellular diffusion pathway represented by the mesaxon cleft. 5. In de-sheathed preparations penetration of potassium ions is still more rapid, an effect which is postulated to result from damage to the perineurium, and the consequent production of a shorter, intracellular diffusion channel through the glial system.

Bending Moments in Free-Swimming Flagella

Abstract: The bending of a flagellum, such as the flagellum which forms the tail of a sea-urchin spermatozoon, is the result of active mechanochemical processes occurring within the flagellum itself, which cause it to bend actively throughout its length (Gray, 1955; Machin, 1958). To understand how flagella operate, we must understand not only the mechanisms which generate bending, but also the control mechanisms which initiate and coordinate the active bending of different parts of the flagellum in order to generate smoothly propagated bending waves which will efficiently propel a cell.

Chemotactic Turning Behaviour of Tubularia Spermatozoa

Abstract: 1. The movements of Tubularia spermatozoa in the vicinity of micropipettes filled with extracts of female hydranths, which chemotactically attract the spermatozoa, have been recorded by multiple-flash photomicrography. 2. When a spermatozoon turns in response to a chemotactic stimulus, the flagellum continues to beat, with a highly asymmetrical pattern of bending, during the turn. 3. The magnitude of the turn, particularly the duration of the period of asymmetrical beating, is variable, but each spermatozoon is only able to make turns in one direction, relative to its own body. 4. Most of the behaviour of these spermatozoa may be explained if the turning mechanism is activated when the spermatozoon detects a decreasing concentration of the chemotactant.

Sensory Control of Abdomen Posture in Flying Locusts

Abstract: 1. A flying tethered locust elevates its abdomen slightly in response to increased, and depresses it greatly in response to decreased, velocities of the relative wind over the head. 2. The wind-velocity dependence and time course of abdomen movement are very similar to those of forewing twist control on the downstroke. The two responses probably work in concert to rotate the animal into a dive when flying speed has fallen critically close to staffing speed. 3. The wind-velocity monitor is provided by a specific group of cephalic wind-receptor hairs. 4. The abdomen response is almost completely absent in tethered locusts which are temporarily flightless, suggesting the presence of a neuronal switch operated by the flight mechanism. Supported by National Science Foundation Grant no. B9-0425R and funds from Cornell University's Division of Biological Sciences.

Water balance in the firebrat, thermobia domestica (packard) the site of uptake of water from the atmosphere

Abstract: 1. Occlusion of the anus prevents the uptake of water from subsaturated atmospheres. 2. It is suggested that the site of uptake is the rectum. 3. The implications of this finding are discussed in relation to other reported cases of uptake.

Salt and water balance in salmon smolts.

Abstract: 1. Salmon smolts adapted to sea water maintain a high rate of turnover of both sodium and chloride, but when adapted to fresh water the rate of turnover is low. 2. Only a small part of the influx takes place through the gut. 3. On immediate transfer from sea water to dilute sea water or to fresh water the influxes decline rapidly, but on transfer from fresh water to sea water the restoration of the fluxes takes place slowly. 4. The alternative hypotheses that the rapid changes are due to exchange diffusion or to rapid adjustments of the sodium pump are discussed.

A Study of the Effect of Temperature Changes on the Respiratory Pumps of the Rainbow Trout

Abstract: 1. Trout subjected to changes in water temperature (1°/3 min.) between 15° and 30° C. showed a number of responses in their ventilation and cardiac mechanisms. 2. Ventilation rate increased slowly over the range 15°-21° C., but increased more rapidly at higher temperatures (21°-26°, Q 10=2.34; 26°-28°, Q 10=4.02). Cardiac frequency fell markedly about 26° C., and this bradycardia suggests that above this temperature the ventilation mechanism is inadequate to maintain a sufficient level of blood P o . Possibly this insufficiency results from a failure of the pumping mechanism to increase or even maintain a large minute volume at high frequencies. 3. Pressure recordings indicate those parts of the ventilatory mechanism which are mainly involved in these responses. Increases in the buccal, opercular, and mean differential pressures indicated that the volume of water pumped across the gills increased during the initial stages of warming and only at higher temperatures did frequency become involved. Variability in the balance between the buccal and opercular pumps among individual trout becomes even more apparent under temperature stress, as in some cases the opercular pumps seem to be mainly involved in the increased ventilation but not always. 4. The action of the buccal and opercular pumps seems well co-ordinated, especially at intermediate temperatures, but serious uncouplings occur at higher temperatures as indicated by the shape of the pressure waveforms and especially the appearance of double reversals in the differential pressure curve. 5. The relationship between cardiac and ventilatory cycles was not studied in great detail, but there were certainly indications of changes in coupling. However, it was clear that the two rhythms do not always become phase-locked even at high temperatures. 6. The effect of changing temperature on the physical environment of the fish is discussed in relation to these observed responses.

Aerodynamics of Gliding Flight of a Black Vulture Coragyps Atratus

Abstract: 1. A black vulture (mass = 1.79 kg) gliding freely in a wind tunnel adjusted its wing span and wing area as its air speed and glide angle changed from 9.9 to 16.8 m/s and from 4.8° to 7.9°, respectively. 2. The minimum sinking speed was 1.09 m/s at an air speed of 11.3 m/s. 3. The maximum ratio of lift to drag forces was 11.6 at an air speed of 13.9 m/s. 4. Parasite drag coefficients for the vulture are similar to those for conventional airfoils and do not support the contention that black vultures have unusually low values of parasite drag.

Ionic content of haemolymph in the cockroach, Periplaneta americana. A critical analysis.

Abstract: 1. The haemolymph of the American cockroach, Periplaneta americana , has been analysed for Na + , K + and Ca 2+ ions in different experimental conditions. 2. The ionic content of the haemolymph is maintained constant after the first larval instar. It is characterized by a rather high K + level and a particularly large variability which could be related either to the nature of the diet (lettuce) or to numerous alterations of the blood and tissues in relation to the moulting cycle. 3. The regulation of this ionic content when the animal is given different diets is particularly effective. Starvation results in a decrease in the mean ionic concentration in the blood, this decrease following a pronounced increase of the Na + and K + levels when starvation is associated with dehydration. The blood K + level can be raised artificially with high K + diets (lettuce leaves or high K + saline) but is then very variable. These results are discussed in terms of absorption, excretion and storage mechanisms. 4. The analysis of blood samples collected successively from the dorsal thorax of different individuals shows that, when the animals are fed normally, the ionic composition varies widely, showing that in these conditions the haemolymph is not homogenous. 5. Serial measurements of blood ions in different regions of the animal show unequal distribution of Na + , Ka + and Ca + . This result is discussed in view of the very special circulatory system of insects when compared with that of vertebrates. 6. The overall picture of insect blood which can be drawn from these experiments is that the complexity of the regulatory system together with the fact that the circulatory system is open and lacunous allows relatively wide variations in the ionic concentration to occur on both sides of a genetically fixed mean. This particular feature must be taken into account when one considers the physiological role of blood ions in mechanisms such as excitation, conduction or muscular contraction.