Showing papers in "The Journal of Experimental Biology in 1967"

The effect of hypoxia upon the partial pressure of gases in the blood and water afferent and efferent to the gills of rainbow trout

Abstract: 1. The rate of oxygen uptake by rainbow trout does not alter during progressive deoxygenation of the environment. Blood lactate, however, shows a significant increase, indicating an increase in anaerobic metabolism during hypoxia. 2. The percentage utilization of oxygen from the water decreased from 55% to approximately 20% during hypoxia and was associated with a 13-fold increase in ventilation volume. 3. The arterial blood of a trout resting in aerated water was 95-100% saturated: the P o 2 was 122 mm. Hg and the P co 2 was 1-1.5 mm. Hg. 4. The venous blood of a resting trout was 70% saturated, had a P o 2 of 35 mm. Hg and a P co 2 , of 2.5 mm. Hg. 5. During hypoxia the percentage saturation of the arterial blood decreased to 37% and that of the venous blood to 3%. The P o 2 in the arterial blood was 10 mm. Hg; in the venous blood, 6 mm. Hg. The P co 2 in the arterial blood was 3.5-4 mm. Hg; in the venous blood, 4.5-5.00 mm. Hg respectively. 6. The ability of the fish to withstand hypoxia was related to the oxygen capacity of the blood, which was on average 9 vol.%. The red blood cells swelled during hypoxia, the hematocrit increased, but the red cell count did not alter. 7. Blood pH was 7.7, falling to 7.4 during hypoxia. 8. Cardiac output did not change during progressive hypoxia in the water, stroke volume increased to offset the decrease in heart rate.

The Jump of the Flea: A Study of the Energetics and a Model of the Mechanism

Abstract: 1. The energy requirement of a jump of 3.5 cm. height by the rabbit flea, Spilopsyllus cuniculi , is 2.25 ergs. This must be delivered in 0.75-1.0 msec. over a distance of 0.37-0.5mm., which is not compatible with direct muscular action. 2. The anatomy of the jumping mechanism has been re-examined and its action studied by high-speed cinematography. The following explanation is offered. The main impulse comes from the depression of the metathoracic femur, whose depressor muscle originates on the notum. In the resting position the attachment of the depressor tendon to the femur is over-centre with respect to the trochanter-femoral joint. When the muscle contracts energy is stored in a resilin pad located between notum and pleuron. This energy is released by a second muscle which pulls the depressor tendon away from the over-centre position, thus enabling it to depress the femur. 3. Operations on live fleas have provided evidence in support of the proposed mechanism. 4. The depressor muscle is capable of providing 1.96 ergs on each side. 5. The resilin pad is capable of storing 4 ergs on each side. 6. Species which are better jumpers have larger resilin pads.

Changes in Blood Pressure in the Rainbow Trout During Hypoxia

Abstract: 1. Methods for cannulating the ventral aorta of the trout, which permit the measurement of blood pressure in the unanaesthetized, unrestrained, intact fish are described. 2. Rate and amplitude of breathing and blood pressure in the dorsal and ventral aortae increase during hypoxia. These changes are associated with a marked bradycardia. 3. There are increases in vascular resistance to blood flow in both respiratory and systemic circulations during hypoxia. 4. Post hypoxia is associated with large increases in ventral aortic and dorsal aortic pressures.

Changes in blood pressure, heart rate and breathing rate during moderate swimming activity in rainbow trout.

Abstract: 1. Changes in blood pressure in the dorsal aorta, ventral aorta and subintestinal vein, as well as changes in heart rate and breathing rate during moderate swimming activity in the rainbow trout are reported. 2. Blood pressures both afferent and efferent to the gills increased during swimming and then returned to normal levels within 30 min. after exercise. 3. Venous blood pressure was characterized by periodic increases during swimming. The pressure changes were not in phase with the body movements. 4. Although total venous return to the heart increased during swimming, a decreased blood flow was recorded in the subintestinal vein. 5. Heart rate and breathing rate increased during swimming and then decreased when swimming ceased. 6. Some possible mechanisms regulating heart and breathing rates are discussed.

Respiration and Tracheal Ventilation in Locusts and other Flying Insects

Abstract: 1. New methods were designed for the simultaneous determination of the unidirectional flow of air and the total abdominal pumping in flying locusts, for measurements of the potential and the actual rate of flow caused by thoracic pumping, and for an independent estimate of the total ventilation of the flight system. 2. During rest, flight and recovery in the desert locust, the unidirectional flow caused by abdominal pumping remains small and almost constant at 30 l. air/kg./hr., in through the thoracic spiracles and out through the abdominal ones. The total pumping amounts to about 180 l./kg./hr. in flight of which 70 l. ventilate the thorax and 80 l. the other paits of the body. 3. Abdominal pumping can be blocked reversibly or reduced to insignificance without impairing the wing movements of the desert locust. 4. During average horizontal flight of the desert locust, the thoracic ventilation is about 320 l. air/kg./hr. of which 250 l. are moved by the thoracic pump, but the capacity of this pump is 760 l./kg./hr. and can be increased to at least 950 l./kg./hr. The relatively low efficiency is likely to increase when the abdominal air sacs are deflated due to ingested food, fat or eggs, i.e. when the animal has to lift more. 5. The pressure changes caused by the thoracic pumping only amount to 10-25 mm. H 2 O and are of no mechanical significance for the moving wings. 6. Draught ventilation due to a Bernoulli effect is of no significance in locusts and probably not in dragonflies and wasps. 7. The oxygen in the thorax of flying locusts is reduced by about 5.5 % relative to the atmosphere at sea level. 8. At small to medium relative humidities, and at temperatures between 25 and 30° C. at sea level, the rate of ventilation permits sustained flight of the desert locust without risk of desiccation (Fig. 14). In order to retain a positive water balance at higher air temperatures the locusts must fly at high altitude, and 3 km. is estimated as a maximum for sustained, active flight. 9. Large dragonflies ( Aeshna spp.) depend almost exclusively on thoracic pumping during flight, while large wasps ( Vespa crabro ) depend on abdominal pumping. For both types the metabolic rate is about 100 kcal./kg./hr. during level flight.

Changes of Gas Concentrations in Blood and Water During Moderate Swimming Activity in Rainbow Trout

Abstract: 1. Changes in partial pressures of O 2 and CO 2 in blood and water afferent and efferent to the gills are reported. These variables were measured before, during and after moderate swimming activity in rainbow trout. 2. Neither blood P CO 2 nor water P O 2 , afferent or efferent to the gills, changed markedly before, during or after exercise. 3. Arterial blood was always more than 95% saturated with oxygen. Venous blood was 38% saturated, falling to a minimum of 28% during exercise. 4. P CO 2 of arterial blood was 2.3 mm. Hg. P co 2 of venous blood increased from 5.7 to 8.0 mm. Hg during exercise and remained elevated throughout the recovery period. 5. Cardiac output (calculated using the Fick principle) stroke volume, ventilation volume and the volume of water pumped per breath all increase by a factor of between 4 and 5 during exercise. All tended to remain elevated for between 10 and 30 min. after exercise and then gradually decrease to pre-exercise levels.

Neuro-muscular control of dipteran flight

Abstract: 1. Electrical activity from the indirect, myogenic muscles of calliphorid flies was recorded during flight. The animals were suspended from an aerodynamic balance in the laminar air-stream from a wind-tunnel. Muscle action potentials, recorded with 25µ wire, were 5-7 msec. in duration, up to 10mV. in amplitude and positive in sign. Frequencies were mostly under 20/sec. 2. Frequencies in all the indirect muscles were similar, but these varied together with changes in aerodynamic power. 3. Frequencies in the indirect muscles of the two sides varied by no more than ± 10% during extreme turns to right or left (only left or only right wing beating). 4. Electrical records from the non-myogenic direct muscles were made during tethered flight. The potentials were 2-4 msec. in duration, up to 2 mV. positive and had frequencies up to 180/sec. 5. A nearly linear positive correlation exists between impulse frequency in the musculus latus (pleurosternal muscle), the inward movement of the pleural wall, and the wingbeat frequency, suggesting that this muscle is the basic frequency determiner. 6. Strong turning behaviour is associated with opposed frequency changes in the pairs of antagonistic adductor and abductor muscles of the wings on the two sides of the body. 7. The musculus dorsoventralis IV (tergo-trochanteral) is activated by a short impulse burst at the beginning of flight. It apparently acts as an oscillation starter. 8. Flight initiation normally requires 30-60 msec. Usually activity begins in the musculus latus, which stiffens the thorax. Then simultaneously the myogenic muscles are activated and the ‘starter’ muscle causes a jump and the beginning of oscillation of the thorax. Then the wings are drawn gradually forward and full wingbeat amplitude develops within the first six wingbeats. Flight begins with maximal lift and wingbeat frequency and a nearly synchronous burst discharge in all the indirect muscles. 9. Power production and the transmission and distribution of power are under separate control. The myogenic indirect motor varies only in total power output, this being influenced by its own state of excitation and by a muscle-controlling wingbeat frequency. Steering is accomplished by non-myogenic direct muscles which are capable of differentially engaging the two wings with the motor.

Sodium and Water Balance in the Cichlid Teleost, Tilapia Mossambica

Abstract: 1. The total body sodium increases from 45.9 µM/g. fish in fresh water to 59.9 µM/g. fish in 200 % sea water. 2. The rate of exchange of sodium increases from 2 µM/g./hr. in fresh water to 60 µM/g./hr. in 100% sea water. 3. The rate of drinking increases from 0.26%/hr. fresh water to 1.6%/hr. in 400% sea water. Even in 200% sea water drinking accounts for only a quarter of the total sodium influx. 4. The permeability to water, as measured by tritiated water, is highest in fresh water and lowest in 200% sea water. The permeabilities to water measured in this way are consistent with the drinking rates determined in sea water and 200% sea water.

The exchange of oxygen and carbon dioxide across the gills of rainbow trout.

Abstract: 1. The effectiveness of oxygen uptake by the blood of rainbow trout ( Salmo gairdneri ) approaches 100%, whereas that for the removal of oxygen from water was only 11-30%. 2. Most of the carbon dioxide is removed from the blood as it passes through the gills, but the effectiveness of carbon dioxide uptake by water is very low, because of the high capacity of water for carbon dioxide compared with oxygen. 3. Moderate exercise had little effect on the effectiveness of gas exchange across the gills. The increased oxygen uptake was facilitated by an increase in the transfer factor of the gills for oxygen. There were small increases in the capacity-rate ratio of blood to water at the gills during moderate exercise. 4. Hypoxia resulted in a marked decrease in the effectiveness of oxygen uptake by the blood, but had little effect on oxygen removal from the water. Gas exchange was facilitated during hypoxia by an increase in transfer factor of the gills, but hindered by an increasing capacity-rate ratio of blood to water at the gills. 5. Gas exchange in an aquatic environment was compared with that in an aerial environment.

Integration of Visual Stimuli by the Crayfish Central Nervous System

Abstract: For the crayfish, properties of visually reacting interneurone types in the optic nerve are described on the basis of single-unit analysis. Sustaining fibres show: (a) ‘surround’ inhibition over the whole retina, including the excitatory field; (b) ‘on’ and ‘off’ effects at field boundaries; (c) a dark discharge in deteriorated preparations; (d) an increase in adapted firing rate and response to flashes in an ‘excited state’ of the preparation; (e) increased overall impulse frequency to fast-moving shadows at frequencies of 2-10/sec. which elicit short bursts. Dimming fibres, having mainly reversed properties, show: (a) bursts followed by adaptation to a lower ferquency level of spikes on light dimming; (b) total inhibition by illumination for times proportional to light intensity; (c) responsiveness to quickly moving shadows. 'Jittery’ movement fibres lack directional sensitivity. For them: (a) total illumination and contrast have, within a wide range, no effect on discharges to moving targets; (b) large, dark cards moved at constant speed are seen only near their visual field boundary; (c) the less predictable the movement of a small dark object is, the longer its excitatory effect lasts; (d) responsiveness of field parts exposed is decreased for long durations; (e) no firing is caused by active or passive eye motions. Space-constant fibres show changed location and size of their excitatory fields with eye position. Their potential visual fields below the horizontal plane are unresponsive, due to inhibition caused mainly by statocyst input. Two eye muscle motor fibres, also under statocyst control, are influenced by light on the limited sensory fields of two pairs of identifiable sustaining fibres. The two motor fibres, which innervate antagonistic muscles, are reversely excited and inhibited by these fields.

The Mechanism of Lung Ventilation in the Tortoise Testudo Graeca Linne

Abstract: 1. An account is given of the gross structure of the respiratory system and of the principal muscles involved in ventilation of the tortoise, Testudo graeca . 2. The mechanism of ventilation was investigated by electrophysiological methods. Cannulae inserted into the lung through holes drilled in the shell recorded pressure changes during the cycle of ventilation and simultaneous recordings were made of the forelimbs movements. The pressure changes were triphasic in form, consisting of an initial increase in pressure followed by a fall to a level of 7 cm. water below atmospheric, and again returned to the atmospheric level or usually slightly above. During the pause between individual ventilation cycles, any overshoot gradually declined to the base-line. 3. Electromyograms showed that all phases of the respiratory cycle were active. The increase in pressure was accompanied by activity in the transversus abdominis and in the pectoralis muscle which draws the shoulder girdle back into the shell. These activities increase the pressure in the peritoneal cavity, which is transmitted to the lung. During the opposite phase of the cycle, the obliquus abdominis and serratus major muscles are active. This increases the volume of the peritoneal cavity and leads to the reduction in intrapulmonary pressure below atmospheric. 4. Activity recorded from the opener and closer muscles of the glottis showed that the glottis is dilated during the first two parts of the cycle but not during the final recompression phase. 5. The respiratory rhythm does not appear to be composed of brief periods of ventilation activity followed by prolonged pauses, as supposed by many authors. These differences may relate to the species investigated. 6. No evidence was found for significant differences in pressure between the right and left lungs or between the anterior and posterior chambers of the lung on one side. 7. It is concluded that the mechanism producing ventilation in the tortoise takes advantage of the only possible way of changing the volume of the thoracico-peritoneal cavity, namely by altering the position of the limb flanks. Both expiratory and inspiratory movements are active.

Stepping Patterns in Tarantula Spiders

Abstract: 1. A descriptive model for the walking patterns of eight-legged animals similar to one applicable to some insects is presented. Data from films of walking tarantulas are compared to the gaits predicted by the model. 2. The model is found to be inapplicable to the tarantula data in two important respects. Some of the common walking patterns of the tarantulas are not predicted by the model, and the several patterns found are not correlated with frequency differences. 3. The tarantula gaits are best described in terms of the phase-relationships between leg pairs. Bilaterally opposite legs and segmentally adjacent legs tend to be used in antiphase. There is much phase variation, giving different stepping sequences, but this variation is by and large not correlated with speed. 4. Incapacitation of some of the spider9s legs results in adaptive changes in phase-coupling between the other legs. 5. A mechanistic model which could explain both insect and spider data is tentatively suggested. It is based on negative coupling between the oscillators controlling each leg.

Flight in Drosophila. II. Variations in stroke parameters and wing contour.

Abstract: 1. In tethered flight in a wind tunnel fruit-flies adjust lift and thrust by shifting the horizontal component of the lower extreme wing position. The upper extreme wing position is nearly constant. 2. Stroke angle and stroke plane are fully interdependent parameters. 3. Angle of attack varies along the length of the wing; no length-wise twisting occurs. 4. Angle of attack varies with flying speed; pitch is unchanged as speed is increased. 5. These characteristics suggest that the flight machinery of fruit-flies is considerably simpler than that of larger flying animals.

Respiratory Function in the South American Lungfish, Lepidosiren Paradoxa (Fitz)

Abstract: 1. Respiratory properties of blood and pattern of branchial and pulmonary gas exchange have been studied in twelve specimens of the South American lungfish, Lepidosiren paradoxa (Fitz). 2. Haematocrit ranged from 14 to 19% and blood oxygen capacity from 4.9 to 6.8 vol. %. The blood had a high affinity for O2 with a P 50 value of 10.5 mm. Hg at P co2 6 mm. Hg and temperature 23° C. The Bohr effect was low. 3. The CO2 dissociation curves show a steep ascending slope resulting in a relatively high CO2 combining power at physiological values of blood P co2 The Haldane effect was small. Buffering capacity of oxygenated whole blood was high and exceeded that in typical water breathers. 4. Air breathing was prominent and intervals between air breaths varied from 3 to 10 min. Branchial respiratory movements were extremely shallow and showed a labile frequency. Air breathing was stimulated by hypoxic and hypercarbic water while hyperoxygenated water had no effect. Branchial respiratory rate showed a marked acceleration in response to mechanical agitation of the water. 5. Gas exchange was predominantly carried out by pulmonary breathing. In less than 10 min. the P O2 of expired gas dropped from 150 mm. Hg to less than 30 mm. Hg. The shallow branchial breathing with very low ventilation values resulted in a low O2 uptake via the gills. 6. Blood-gas analysis documented a clear selective passage of blood through the only partially divided heart. A consistently higher P O2 in dorsal aortic than in pulmonary arterial blood indicates a preferential passage of pulmonary venous blood to the anterior branchial arteries giving rise to most of the systemic circulation while systemic venous blood was largely conveyed to the most posterior branchial arteries giving rise to the pulmonary arteries. 7. The oxygen uptake for fish resting in water with access to air averaged 53.4 ml./hr./kg. Exposure to air lowered the O2 uptake markedly. 8. The increased importance of pulmonary breathing in Lepidosiren is discussed in relation to the transition from water breathing to air breathing. This investigation was supported by grant G.B. 358 from the National Science Foundation and grants H.E. 0845 and H.E. 01892 from the National Institute of Health. This work was carried out during the tenure of an Established Investigatorship of the American Heart Association.

Hyperphagia in the Blowfly

Abstract: 1. The nervous mechanism controlling feeding in the blowfly has been re-investigated. 2. The data presented reveal that the mechanism is more complex than originally thought but can be readily understood in the same basic terms as the original model, that is, the interaction of peripheral sensory excitation and internal inhibition. 3. The old model becomes the new by the addition of two new sources of internal inhibition--body-wall stretch receptors and a thoracic ganglion locomotor centre. 4. The several sources of internal inhibition are not equal in their inhibitory effect; removing body-wall stretch receptors produces a more vigorous hyperphagia than removing the foregut stretch receptor.

Command interneurons in the crayfish central nervous system

Abstract: The motor effects evoked by stimulation of each of eight command fibres in the circumoesophageal commissures of the crayfish are described. The fibres obtained appeared to have widespread connexions in all or most of the lower ganglia. For certain fibres the response was stronger on the homolateral side of the animal; for others it was symmetrical. The frequency of stimulation of a command fibre generally had a pronounced influence on the speed of the evoked response. In addition, segments of the total response could be elicited selectively by alteration of the frequency and duration of stimulation. Although the responses associated with most of the fibres were not sensitive to the fine temporal pattern of the applied stimulation, for one fibre the motor output depended clearly on the spacing of the stimulating pulses.

The circadian flight activity of the mosquito Anopheles Gambiae: phase setting by the light régime.

Abstract: 1. The circadian cycle of flight activity of individual, sugar-fed, Anopheles gambiae females has been studied, using the flight-sound as an indicator of activity. 2. In an LD 12:12 regime (alternating 12 hr. light: 12 hr. dark), activity peaks follow both light-off and light-on. The mosquitoes are moderately active in the dark, but are inactive in the light after the first half-hour. 3. If the light period is extended, the activity is delayed until light-off. Light appears to have an inhibitory effect, but the insects may show some activity towards the end of a 48 hr. light period. 4. Cyclical activity continues in constant dark with a period of approximately 23 hr. A late light-off resets the cycle; an early light-off does not. 5. When the LD 12:12 regime is advanced by 6 hr. the cycle is re-entrained within 2-3 days. Light in the second half of the subjective night appears to advance the cycle. 6. It is suggested that the activity is controlled by an endogenous rhythm which possibly controls the release of an excitatory hormone. The effect of light may be mediated through an inhibitory hormone.

Sequential changes in the adenosinetriphosphatase activity and the electrolyte excretory capacity of the nasal glands of the duck (anas platyrhynchos) during the period of adaptation to hypertonic saline

Abstract: 1. Regardless of the composition of the incubation medium, the nasal gland tissue from ducks adapted to hypertonic saline always released inorganic phosphate from the ATP in the medium at a higher rate than tissue derived from freshwater-adapted ducks. 2. Changes in the nasal gland ATP-ase activities during the period of adaptation to saline followed the same time course as the changes which occurred in the sodium-excretory capacity of the tissue. 3. Adaptation to saline resulted in a three- to fourfold increase in the weight-specific ATP-ase activity which was accompanied by a three- to fourfold increase in the weight-specific sodium-excretory capacity. 4. In the saline-adapted birds a positive correlation was found between the sodium-excretory capacity of the nasal gland tissue and the corresponding ATP-ase activity. 5. The moles of sodium excreted per mole of ATP hydrolysed was constant irrespective of whether the birds were adapted to either fresh water or salt water. 6. Concommitant with the changes in weight-specific sodium excretion and ATP-ase activity, an increase in the sodium concentration of the nasal gland fluid was observed. An approximately twofold increase in nasal gland weight also occurred during this period. 7. All changes which were observed to occur during the period of adaptation to saline were reversed when the birds were returned to fresh water. 8. The observed changes in enzyme activity and sodium excretory rates of the nasal glands are discussed in relation to possible cellular changes which might occur and their importance relative to the birds's ability to adapt to a marine environment. This work was supported by research grants to W.N.H. from the National Science Foundation (Grant no. GB3896) and the Commmittee on Research, University of California.

Impulse identification and axon mapping of the nine neurons in the cardiac ganglion of the lobster Homarus americanus.

Abstract: 1. Simultaneous recording from several pairs of electrodes placed along the ganglion and certain efferent nerves, during stimulation of other efferents, allows the course of antidromic impulses in each stimulated axon to be mapped. 2. These impulses disappear as they approach their somata, being incapable of invading them, a fact which permits identification of a particular efferent axon with a particular soma. 3. By these means the courses of all such efferent axons, and their corresponding somata, have been determined. These all belong to the five large cells. 4. The impulses from each such axon occurring during the spontaneous burst can be identified, as can impulses from each small cell. 5. Each large-cell axon appears to be inexcitable until it is a few mm from the soma. 6. If the axon branches within this inexcitable region, the branches tend to fire impulses independently. 7. The technique of cell identification opens the way to a more complete analysis of the ganglion9s activity and the synaptic interactions which produce it.

Hormonal Control of Excretion in the American Cockroach I. Release of a Diuretic Hormone from the Terminal Abdominal Ganglion

Abstract: 1. When adult male cockroaches are deprived of water for 3 days the subsequent overcompensation of water ingestion causes the release of a diuretic hormone into the blood. 2. Ligation experiments indicate that the hormone was released from the posterior part of the abdomen. 3. The testing of various tissues extirpated from within this region revealed that only extracts of the terminal abdominal ganglion could promote diuresis. 4. Homogenates of ganglia from normal animals fail to elicit the diuretic response; this and other evidence suggests the presence of an antidiuretic hormone.

Zinc regulation in the freshwater crayfish (including some comparative copper analyses).

Abstract: 1. Zinc concentrations in the freshwater crayfish Austropotamobius pallipes pallipes normally range from about I µ g./g. in the blood to 100 µ g./g. in the hepatopancreas. 2. The permeability of the body surface to zinc is very low. Long exposure to concentrations exceeding that of the blood is required to increase the internal tissue zinc concentrations appreciably. 3. Much of the zinc which is absorbed from solution appears to be adsorbed on to the gill and shell surfaces. 4. Most of the body zinc is obtained from food. 5. The hepatopancreas is the principal organ of zinc regulation. It can absorb excess zinc from the stomach fluid and can remove excess zinc if this is injected into the blood. 6. Very little of the excess zinc in the hepatopancreas can be lost in the urine or across the body surface. Zinc is lost only when the animal feeds and faeces are produced to which it can bind. 7. As the amount of zinc in the food increases, a smaller percentage of it is absorbed by the hepatopancreas and more is lost in the faeces. 8. Regulation of zinc seems to depend on changes in the hepatopancreas/stomach-fluid ratio. These alter the availability of zinc for removal in the faeces according to the concentration in the hepatopancreas. 9. There is no close relationship between the behaviour of zinc and copper although zinc is bound to blood proteins some of which are haemocyanins. 10. Differences in the methods of regulation between the freshwater crayfish and the marine lobster may represent changes which have occurred during the penetration of the crayfish into fresh water.

Relationships between photoperiodism and circadian rhythms of activity in the house finch.

Abstract: 1. The Bunning hypothesis proposes that many rhythmic physiological processes, including photoperiodic responsiveness, are all based upon a single, endogenous circadian time-measuring system (‘die physiologische Uhr’). We have attempted to test this hypothesis by examining correlations between the circadian waking-sleeping rhythm of the house finch ( Carpodacus mexicanus ), and the circadian rhythm of sensitivity to light, which underlies the photoperiodic testicular responses of this species. 2. Experimental techniques included (1) comparisons of locomotor activity patterns induced by specific non-daily light cycles which stimulate gametogenesis (LD 6:30 and 6:54) with those induced by other cycles which are non-inductive (LD 6:18, 6:42 and 6:66); (2) comparisons of gametogenesis resulting from light cycles which produce large phase-lead in the activity rhythms and thereby result in photic stimulation late in the ‘subjective day’ (LD 6:20 and 3:23) with results from similar cycles which cause no phase lead (LD 6:16 and 3:19); and (3) comparisons of gametogenesis under free-running (unsynchronized) conditions in which a 6 hr. stimulus was intermittently administered early in the ‘subjective day’, with other treatments in which the same stimulus was administered late in the ‘subjective day’. 3. In all experimental series, when only group responses are considered, there were clear and strong correlations between testicular growth and the patterns observed in locomotor activity. The nature of the large intra-group variability, however, convinces us that the Bunning hypothesis, as here interpreted, is inadequate to account for all the results. Either the two circadian rhythms may be independent, similar systems; or, if there is a single ‘master clock’, the two manifestations of this timing system are apparently not phase-locked under artificial laboratory conditions. It is not clear to us how these two alternatives are experimentally distinguishable.

The Strength of the Pigeon's Wing Bones in Relation to Their Function

Abstract: 1. Simple methods are described for applying known bending and twisting moments to pigeon bones. The ultimate bending and torsional strengths of the humerus and radio-ulna are determined. 2. Lift distributions are calculated from a strip diagram on the assumption that local lift coefficient is constant across the span. The position of the centre of lift is calculated for ( a ) gliding, in which the relative air speed is entirely due to the forward motion of the bird; and ( b ) hovering, in which it is entirely due to rotation of the wing about the shoulder joint. 3. Estimates of the ultimate load factor of the humerus in bending and twisting yielded 8.8 and 9.0 respectively in gliding, and 5.7 and 5.6 in hovering. Corresponding figures for the radio-ulna were 6.9 and 9.1 in gliding, and 4.0 and 5.1 in hovering. 4. The pectoralis insertion is strong enough to apply 4.2 g in gliding and 2.9 g in hovering, so the muscles would be forcibly extended before any danger could arise of the bones being broken by excessive lift. 5. A lift coefficient of at least 3.4 is achieved during the downstroke of hovering.

Flight in Drosophila : III. Aerodynamic Characteristics of Fly Wing Sand Wing Models

Abstract: 1. The variation of the lift and drag of fruit-fly wings with angle of attack and velocity was compared with that of thin plates. 2. High drag and low ratios of lift to drag characterized these airfoils, the primary difference being the absence of stalling in the fly wings. 3. Flow photographs and determinations of stall point on thin plates suggested that the fly wing behaves as if encountering a Reynolds number below the actual value. 4. At positive angles of attack camber improved the aerodynamic characteristics of fly wings; at negative angles uncambered wings were superior. 5. The structural basis for the performance of fly wings and the relationship of their characteristics to their opening conditions are discussed.

Flight in Drosophila

Abstract: 1. The variation of the lift and drag of fruit-fly wings with angle of attack and velocity was compared with that of thin plates. 2. High drag and low ratios of lift to drag characterized these airfoils, the primary difference being the absence of stalling in the fly wings. 3. Flow photographs and determinations of stall point on thin plates suggested that the fly wing behaves as if encountering a Reynolds number below the actual value. 4. At positive angles of attack camber improved the aerodynamic characteristics of fly wings; at negative angles uncambered wings were superior. 5. The structural basis for the performance of fly wings and the relationship of their characteristics to their opening conditions are discussed.

Sodium, chloride and water balance of the intertidal teleost, Xiphister atropurpurpureus. II. The role of the kidney and the gut.

Abstract: 1. The rate of loss of sodium, chloride and water via the urine and the rate of intake of sodium, chloride and water by ingestion of the medium was determined for the euryhaline teleost, Xiphister atropurpureus . 2. The urinary losses of sodium and chloride were approximately 0.5 mM/kg. fish/day in both 100 % sea water (480 mM-Na/kg.) and 10% sea water. The ingestion of sodium and chloride by drinking the medium amounted to approximately 4 mM/kg. fish/day in 100% sea water and approximately 0.1 mM/kg. fish/day in 10% sea water. 3. The low rate of urine flow in 10 % sea water and the low drinking rate in 100 % sea water indicate a relative impermeability to water in both salinities.

Neural mechanism by which controlling inputs influence motor output in the flying locust.

Abstract: 1. The central nervous system of the flying locust generates a pattern of alternating bursts of impulses in the elevator and depressor motor neurons (Wilson, 1961). The mechanism by which controlling inputs modify this output pattern is analysed in this paper. 2. During roll turns and other flight manoeuvres the average number of impulses per burst (average burst length) changes in certain motor neurons. Changes in average burst length develop slowly, over tens of wingbeat cycles, even in response to the abrupt changes in input which result from electrical stimulation of sensory nerves. 3. In addition to the slow changes in average burst length which are elicited by controlling inputs, more rapid changes in burst length sometimes occur. During this rapid variation a longer burst is usually followed by a shorter burst, probably because the motor neuron is less excitable after a longer burst of activity. Burst length varies independently in different motor neurons. Both findings suggest that much of the rapid variation in burst length is due to changes occurring within the individual motor neurons, and is not a response to rapid changes in controlling inputs. 4. Under all conditions, changes in the number of impulses per burst are correlated with small changes in the relative timing of the burst; the longer bursts produced by a motor neuron begin slightly earlier in the wingbeat cycle. This implies that the factors which cause variation in the length of the bursts are also responsible for producing the variation in the timing of the bursts. 5. All of the observations can be explained on one assumption: that the only effect of controlling inputs is to cause slow changes in the ‘average excitation’ of individual motor neurons. Thus sensory and central control of the flight pattern generating system appears to be slow control over the average performance, rather than fast control over performance in a particular cycle.

Homing of single pigeons--analysis of tracks.

Abstract: 1. Pigeons trained by releases along a constant compass line were repeatedly tracked to their lofts from the same training points 30-50 miles away. Their tracks differed from day to day by several miles, and the birds usually did not follow any obvious landmarks. 2. The pigeons were released from new release points and on many of the tracks followed a definite sequence of orientation methods: the birds began flying in the same compass direction that had got them home from the training point, then they apparently switched to a rather accurate navigation method which got them to within 10 miles of the loft, where they seemed to pilot by a few familiar landmarks to the loft entrance. 3. There is no evidence that most of the pigeons learned or could use landmarks extensively more than 10 miles from the loft, even over area which they crossed more than twenty times. 4. The flight of pigeons from the training points and new release points at distances of 13 miles or more depended strictly on the visibility of the sun.

Spontaneously induced rhythm of tidal periodicity in laboratory-reared Carcinus.

Abstract: 1. Laboratory-reared shore crabs show circadian rhythmicity which is transformed to approximate tidal rhythmicity after a period of chilling to 4°C. 2. Periodogram analysis of the results characterizes the periodicity of the two types of rhythm, which suggest that the ability to show a rhythm of tidal periodicity is an inherited feature of shore-crab physiology.

The effect of some anions and cations upon the fluxes and net uptake of chloride in the larva of Aëdes aegypti (L.), and the nature of the uptake mechanisms for sodium and chloride.

Abstract: 1. The anal papillae of the aquatic larva of Aedes aegypti are responsible for 90% of the steady-state exchange of chloride. 2. The relationships between chloride flux and external chloride concentration are approximately described by the Michaelis equation. 3. There is net uptake of chloride, independent of uptake of sodium, from KCl, CaCl 2 and NH 4 Cl, probably in exchange for OH9 or HCO9 3 , but the rate is much slower than from NaCl. The following ions stimulate influx of chloride from 0.1 mM/l. KCl: H + = Na + + The following ions inhibit it: OH9 > HCO9 3 > NO9 3 . 4. Movements of sodium and chloride ions are explicable in terms of an anionic and a cationic carrier located in an osmotic barrier in the papillae, the carriers being functionally coupled to sodium and chloride pumps located at the inner surface of the barrier. 5. An attempt is made to relate these findings to recent electron microscopical studies of the papillae.