Showing papers in "The Journal of Experimental Biology in 1971"

The Electric Sense of Sharks and Rays

Abstract: 1. Previous experiments have demonstrated that ( a ) the shark Scyliorhinus canicula and the ray Raja clavata are extremely sensitive to weak electric fields; ( b ) their electrical sensitivity is due to the ampullae of Lorenzini; ( c ) the sharks and rays can be stimulated by the bioelectric fields emanating from the flatfish Pleuronectes platessa . 2. When hungry, Scyliorhinus and Raja perform well-aimed feeding responses to flatfish, even if the prey have covered themselves with sand. The object of the present study was to determine whether the sharks and rays use the bioelectric fields of the flatfish to detect the position of their prey. 3. To analyse the feeding responses of the sharks and rays, a flatfish was put into an agar chamber. The predators responded to the so screened prey from the same distance, and tried to feed on it in the same way as if there were no agar at all. As the flatfish in the agar chamber was completely hidden from view, the sharks and rays were thus shown not to need visual contact to locate the prey. 4. If the agar chamber was filled with cut-up pieces of whiting, the sharks and rays did not respond to the food, although the odour of whiting juice normally attracts them strongly. Therefore, the sharks and rays did not detect the position of the agarscreened flatfish by smell. 5. The feeding responses to the flatfish could be entirely abolished by covering the agar chamber with a very thin sheet of plastic. The mechanical attenuation offered by the plastic film was too weak to explain its dramatic inhibitory effect, and, thus, a purely mechanical detection of the agar-screened flatfish without plastic film was also ruled out. 6. As the responses to the agar-screened flatfish were not merely due to visual, chemical, or mechanical stimuli, it was tentatively concluded that the sharks and rays perceived the prey electrically. This conclusion was fully in agreement with the results of the experiments, for the agar chamber did not appreciably distort the bioelectric fields of the flatfish, and the electrical impedance of the plastic film was extremely high. 7. Further, the bioelectric field of a flatfish was simulated with a pair of electrodes, buried in the sand. Now, the sharks and rays displayed exactly the same feeding responses to the electrodes as they did previously to the real prey. This crucial experiment confirmed the electrical hypothesis in a very direct way. 8. The experiments described demonstrate clearly that the shark Scyliorhinus canicula and the ray Raja clavata make a biologically significant use of their electrical sensitivity. Therefore, we now are justified in accrediting the animals with an electric sense and in designating the ampullae of Lorenzini as electroreceptors . 9. When the sharks and rays were offered a piece of whiting in the vicinity of two electrodes simulating a flatfish, they were attracted by the odour of the food but usually performed their well-aimed responses to the electrodes. Thus, at short range, the electric fields act as a much stronger directive force than do the visual and chemical stimuli. Only direct mechanical contact dominates over the electrical stimuli. 10. Theoretically, the sharks and rays can detect the electric fields resulting from ceanic and tidal currents. Whether they make use of the available information for orientation in the open sea is not yet known. Furthermore, the observations and measurements described indicate that, in studying shark attacks, the electric fields of the prey and the electric sense of the predators should be taken into account. Present address: Department of Neurosciences, School of Medicine, University of California, San DiegoLa Jolla, California 92037.

Acoustic location of prey by barn owls (Tyto alba).

Abstract: 1. Barn owls ( Tyto alba ) can locate prey in total darkness using only the sense of hearing, with an error of less than I° in both the vertical and horizontal planes. 2. Differences between the behaviour of barn owls flying at prey in complete darkness (analysed from films taken under infra-red illumination) and their behaviour in the light are correlated with the problems they must face in acoustic orientation. 3. Experiments with owls trained to strike a concealed loudspeaker show that they depend on frequencies of sound above 5 kHz. 4. Measurements of sound pressure in the region of the owl9s eardrum, made with a probe-tube microphone while moving a loudspeaker around the owl9s head, reveal that for frequencies above 8-5 kHz the ear is highly directional. At such frequencies, regions of high sensitivity (tightly isolated by peripheral regions of low sensitivity) are directed along different paths for the two ears. 5. These regions of good sensitivity are correlated with the asymmetry of the barn owl9s external ears. Movements of a flap of skin in front of the ear opening changes the overall directional sensitivity patterns by redirecting the regions of maximum sensitivity. 6. A theory is presented to explain how a barn owl might locate the position of a sound source by moving its head until the intensity of all frequencies comprising a complex sound is brought to a maximum in both ears (aided perhaps by differences in inter-aural time delay that are enhanced by intensity disparities).

The swimming energetics of trout. II. Oxygen consumption and swimming efficiency.

Abstract: 1. The oxygen consumption of rainbow trout was measured at a variety of subfatigue swimming speeds, at a temperature of 15 %C. Five groups of fish were used, a control group and four groups with extra drag loads attached to the body. 2. The logarithm of oxygen consumption was linearly related to swimming speed in all five groups, the slope of the relationship increasing with the size of the extra drag load. The mean standard rate of oxygen consumption was 72.5 mg O 2 /kg wet weight/h. The active rate of oxygen consumption was highest for the control group (628 mg O 2 /kg/h) and fell with increasing size of the attached drag load. The active rate for the control group was high in comparison with other salmonid fish, and in comparison with the value expected for the fish. This was not a result of the extra drag loads in the other groups. No explanation for this high value can be found. 3. The critical swimming speed for a 60 min test period was 58.1 cm/sec (2.0 body lengths/sec) for the control group. The values for the critical swimming speeds were slightly higher than those measured for the same species in a previous paper (Webb, 1971). The difference between the two sets of critical swimming speeds is attributed to seasonal changes in swimming performance. 4. The aerobic efficiency was found to reach values of 14.5-15.5% based on the energy released by aerobic metabolism in comparison with the calculated required thrust. 5. The anaerobic contribution to the total energy budget in increasing-velocity tests is considered to be small, and can be neglected. 6. It is concluded that the efficiency of the muscle system in cruising will be approximately 17-20% over the upper 80% of the cruising-speed range, while the caudal propeller efficiency will increase from about 15-75 % over the same range. 7. Consideration of the efficiency values for the caudal propeller calculated here, and those predicted by Lighthill9s (1969) model of fish propulsion, suggest that the efficiency of the propeller system will reach an optimum value at the maximum cruising speeds of most fish, and will remain close to this value at spring speeds.

The Swimming Energetics of Trout: I. Thrust and Power Output at Cruising Speeds

Abstract: 1. The wavelength, tail-beat frequency and trailing-edge amplitude have been measured for five groups of rainbow trout at various subfatigue cruising speeds. Four groups of fish were fitted with extra drag loads. The swimming mode was anguilliform by definition, but is probably best considered as intermediate between this and the carangiform mode. 2. The wavelength of the propulsive wave represented 0.76 of the body length. The specific amplitude (amplitude/length) tended to reach a maximum value of 0.175 at tail-beat frequencies approaching 5/sec. 3. The product of frequency and specific amplitude was found to be linearly related to swimming speed in all five groups of fish. 4. The critical swimming speed for the non-loaded control group was 1.73 body length/sec, and fell in groups 1-4 as the magnitude of the extra drag loads increased. The critical swimming speed for the control group is low for salmonids, probably as a result of the unfavourable history of the fish. 5. A method is described for calculating the drag of a swimming fish from the effects of the extra loads on the characteristics of the propulsive wave. It was found that thrust, T = 7.9 (swimming speed) 1.79 . The thrust was approximately 2.8 times greater than that required for an equivalent straight rigid vehicle. 6. It was calculated that the power output of the red muscle system would need to be about 0.48-0.77 ergs/sec/g muscle to overcome the drag of the fish at cruising speeds. 7. The power output of the fish was compared with values calculated by means of mathematical models proposed by Taylor and Lighthill. It was found that the fish did not fit the assumptions made in Taylor9s model, and so power output calculations were not comparable with those calculated in the present paper. Lighthill9s model was found to give values which were within 5 % of the values calculated here at higher swimming speeds. At lower swimming speeds the values were up to about 50 % lower than expected because again the fish did not fit the assumptions involved. 8. The relationship between thrust and swimming speed was extended into the sprint-speed range. It was calculated that fish could reach a maximum sprint speed maintained for 1 sec, provided that drag was reduced by about a half, or that the power required was that to accelerate the fish to that speed.

Bend propagation by a sliding filament model for flagella

Abstract: 1. If active sliding occurs between flagellar filaments, as suggested for the sliding filament mechanism for muscular contraction, it will generate positive bending in one direction along the flagellum and negative bending in the opposite direction. Bends will therefore be propagated automatically if the sliding process is activated by bending. 2. The active bending moment required to match the viscous bending moments resulting from the uniform propagation of bending waves can be generated by a simple relationship between the curvature of the flagellum at any point and the magnitude of the moment per unit length generated by the active sliding process at that point. 3. This propagation mechanism incorporates features of the two mechanisms proposed previously for flagellar-bend propagation. The major difficulties which arise when these propagation mechanisms are developed in terms of a ‘local-bending’ model for flagellar bending are avoided when a ‘sliding filament’ model is used. 4. The elastic constants of the flagellum have a minor role in bend propagation, and without additional assumptions their magnitudes cannot be obtained from measurements of the parameters of flagellar bending-wave propagation.

Separation of Receptor and Lamina Potentials in the Electroretinogram of Normal and Mutant Drosophila

Abstract: 1. In Drosophila the retinula cells and the cells in the lamina ganglionaris contribute to the ERG. This is due to extracellular resistance barriers across these cells ; one of these is situated near the proximal ends of the rhabdomeres separating the retinula cell layer from the rest of the fly, the other is situated either within several layers or homogeneously distributed throughout the lamina. Because of their different origin, two components of the ERG, the receptor potential and the lamina potential can be separated experimentally. 2. At high light intensity the receptor potential is larger than the lamina potential. However, under stimulus conditions where the receptor potential is very small ( a ) at low light intensity, ( b ) at high intensity but low flash contrast (Δ I / I ), ( c ) at high frequency of stimulation, the lamina potential exceeds the receptor potential. It is suggested that these properties reflect summation and adaptation of the sensory input within the lamina. The shape of the lamina potential has, under these conditions, the characteristics of a high-pass filter and may improve the fly9s response to high stimulus frequencies. 3. The ERGS of the mutants ebony, tan and opm 2 have normal or nearly normal receptor potentials but at the same time demonstrate severe defects in the lamina potentials. In ebony a fast on-effect at high intensity, and in tan a delayed off-effect at high intensity, are still present. The mutant opm 2 shows very little lamina activity at all. The difference of the defects in the three mutants argues against non-specific current leaks in or around the lamina. Therefore it is most likely that the lamina properties of summation, adaptation, and high-pass filtering, are largely lost in the three mutants. This is supported by behavioural experiments.

The Locomotion of the Cockroach Periplaneta Americana

Abstract: 1. The locomotion of free, intact cockroaches, Periplaneta americana , was studied with the aid of high speed motion pictures. 2. The insects used a single gait, alternating triangle, at all speeds of locomotion 5-80 cm/s) except the very lowest ones (below 5 cm/s). 3. Both forward (protraction) and rearward (retraction) movements of the legs relative to the body decreased in duration as the insect9s rate of forward progression increased, but at different rates. In addition, protraction was usually shorter for the two middle legs than for the remaining four. 4. The ratio of protraction to retraction increased as the locomotor rate increased. The rate of change of this ratio was the same for each of the legs. 5. Phase relationships between adjacent ipsilateral legs were constant at about 0.5 at all walking speeds above about 5 cm/s. Phase between legs in a single segment (i.e. contralateral pairs) was constant at about 0.5 at all speeds. 6. The locomotion of Periplaneta was compared to that of other insects. Despite the differences, a single mechanism could account for walking in each.

Pharmacology of the Malpighian Tubules of Rhodnius and Carausius : The Structure-Activity Relationship of Tryptamine Analogues and the Role of Cyclic Amp

Abstract: 1. 5-Hydroxytryptamine (5-HT) and a few of its derivatives will cause an acceleration of secretion by the isolated Malpighian tubules of Rhodnius prolixus and Carausius morosus . Substitution in the terminal amino group of 5-HT causes little loss of effect, but changes in the indole ring and the hydroxy group in general abolish activity. 2. Most derivatives of 5-HT which do not stimulate secretion, and many other related amines, act as inhibitors of secretion in Rhodnius . This inhibition is probably of the competitive type. 3. Substances which stimulate secretion in Rhodnius are easily washed off the Malpighian tubules, although they will stimulate secretion at very low concentrations By contrast, competitive inhibitors wash away relatively slowly and inhibit only at much higher concentrations. It is suggested therefore that stimulation involves only momentary interactions between stimulant and receptor sites, but that competitive inhibitors spend considerably longer attached to the sites. 4. Cyclic 3',5'-adenosine monophosphate (cyclic AMP) will stimulate secretion by tubules of both Rhodnius and Carausius . Tubules of both species are very sensitive to cyclic AMP, measurable effects being produced at concentrations of 4 x 10-5 M/l in Rhodnius and 10-4 M/l in Carausius . 5. Aminophylline (theophylline ethylene diamine) at a concentration of 10-4 M/l stimulates secretion by Carausius tubules. This compound and other inhibitors of phosphodiesterase have no stimulatory action on Rhodnius tubules, but any such effect may be masked by the adverse reaction of the tubules to the high concentrations necessary. 6. Inhibitors of 5-HT action such as tryptamine and tyramine also inhibit secretion by Rhodnius Malpighian tubules induced by cyclic AMP. This may be due to a dependence of the action of cyclic AMP on the state of the diuretic hormone receptor site. 7. The evidence is consistent with the idea that 5-HT, other stimulant molecules related to 5-HT and the diuretic hormones interact with Malpighian tubule cells of Rhodnius and Carausius at specific sites, probably on the cell membrane facing the haemolymph. As a result of this, secretion is induced, possibly through the action of intracellular cyclic AMP produced as a response.

Innervation of coxal depressor muscles in the cockroach, Periplaneta americana.

Abstract: 1. The innervation of the mesothoracic and metathoracic coxal depressor muscles has been investigated using intracellur microeletrodes. 2. Five motor axons have been found to innervate the coxal depressor muscles; the largest is fast axon, the second largest a slow axon and the three smallest are all inhibitory axons. 3. The fast axon innervates the anterior and posterior coxal depressor muscles as well as parts of the coxal branches of the main leg depressor muscle. The slow innervates all fibres in the coxal branches of the main leg depressor muscle. The three inhibitory axons innervate only those parts of the coxal branches of the main leg depressor muscle which are not innervated by the fast axon. 4. The three inhibitory axons were found to be branches of three different common inhibitory motoneurones.

Temperature Regulation of the Sphinx Moth, Manduca Sexta : I. Flight Energetics and Body Temperature During Free and Tethered Flight

Abstract: 1. The sphinx moth, Manduca sexta , maintained an average thoracic temperature of 40-42 °C during free flight in ambient temperatures (T A ) of about 16-33 °C. In the extremes, the excess of thoracic temperature T Th over T A varied from a mean of 25 °C at 12.5 °C, to a mean of 8 °C at a T A of 35 °C. 2. During tethered flight T Th increased directly with T A , and the excess of T Th over T A varied from about 11-4 °C. 3. The oxygen consumption was about 45-50 C.C. O 2 /g h during free flight from ambient temperatures of 15-30 °C. During captive flight the oxygen consumption was about 21 c.c. O 2 /g h. 4. The wing-beat frequency and amplitude during both free flight and captive flight did not vary significantly with T A . The wing-beat frequency was about the same during free flight and captive flight but the wing-beat amplitude was significantly less in the latter. 5. The moths showed little variation of flight speed with respect to T A on the flight mill. The difference between T Th and T A was strongly correlated with flight speed at low, but not at high, T A . 6. The cooling rate of dead moths was only slightly correlated with air speeds from 2 to 5 m/s. 7. The cooling rate of thoraces without scales was 2.4 times as great as with scales intact at an air flow 2 m/s, but the cooling rate of the abdomen was only slightly increased after the removal of its scales. 8. The data suggest that the rate of metabolism during flight is altered with regard to the flight effort, but not with regard to temperature-regulation. Heat is actively dissipated from the thorax during flight at high T A , or during fast flight when T Th reaches 40 °C or above.

Orientation by jumping spiders in the absence of visual feedback.

Abstract: 1. Jumping spiders turn to face moving objects. These turns are mediated by the lateral eyes. They can be accomplished accurately whether or not the spider sees the relative movement of the stimulus across the retinae which would normally result from such a turn. 2. The spider9s response to an adequate stimulus may be: (i) to make a ‘complete’ turn resulting in fixation by the antero-median eyes; (ii) to make a ‘partial’ turn of 10-20°, whose magnitude is independent of stimulus position, and which does notresult in fixation, or (iii) to ignore it. 3. To be seen, a stimulus must subtend more than 0.7° (slightly less than the distance between receptors) and must move through a minimum angle of about 1°. 4. The probability of a turn being made is greatest for stimuli 40-90° from the spider9s front, and decreases to a low value for stimuli behind the animal, and immediately in front of it. 5. Repeated presentation of a stimulus to one part of the retina results in a rapid decrease to zero of the probability of a turn being made, but turns can still be evoked by moving the stimulus a few degrees to a previously unstimulated part of the retina. Habituation does not affect the sizes of the few turns that are made. Dishabituation can be caused by mechanical stimulation, or it may occur spontaneously. 6. The fields of view of the lateral eyes have been measured in the horizontal plane by blinding each eye and determining the parts of the visual field from which turns could not be evoked. 7. Three kinds of response mediated by the lateral eyes, in addition to turns towards the stimulus, are described.

Desert snails: problems of heat, water and food.

Abstract: Animal material. Sphincterochila boissieri (Charpentier, 1847) is a fairly small snail (average weight about 4 g) with a chalky-white shell. Animals used for laboratory studies were collected in the central Negev near Avdat and Sde Bokher and shipped by air to Duke University. Summer field studies were carried out in the same area, where the mean annual rainfall is less than 100 mm. The rains are concentrated in the winter months, from November to March, and during this period the snails are active, feed, and reproduce. During the remainder of the year the snails presumably remain dormant. Three types of mineral surface material are common in this area: (a) a. firmly packed powdery soil or loess, (b) limestone rocks and pebbles with a granular, disintegrating surface, and (c) broken-up black flint. While Sphincterochila is common in the loesslimestone areas, it is much less common on the flint substratum. Sphincterochila is a mud-eater; that is, after rain it comes out and eats large quantities of the surface material (loess); and, in our experience, also material from the surface of limestone rocks and pebbles. The digestible material contained in this predominantly mineral diet is primarily algae and lichens. Sphincterochila shows no obvious interest in those higher plants which are eaten by other snails in the same area, such as Eremina and Helicella. More detailed information about the ecology of these desert snails has recently become available (Yom-Tov, 1970).

Bird Respiration: Flow Patterns in the Duck Lung

Abstract: 1. A heated thermistor probe was designed to determine the direction of air flow in the respiratory system of birds. The probes did not significantly affect the respiratory rates, tidal volumes, or body temperatures of birds implanted with the probes as compared to unimplanted birds. 2. Air-flow directions were determined in the primary bronchus, the craniomedial secondary bronchi, and the caudodorsal secondary bronchi in the lungs of ducks which were either unanaesthetized and at rest, anaesthetized, or panting due to heat load. 3. The recorded air-flow directions suggested the following patterns of air flow in the duck lung for resting respiration. During inspiration air flows to the posterior air sacs directly from the primary bronchus (the most direct route), without passing through the tertiary bronchi, while air flows towards the anterior air sacs via the caudodorsal secondary bronchi and the tertiary bronchi (thus by-passing the most direct route, the craniomedial secondary bronchi connecting these sacs to the primary bronchus). During expiration air flows from the anterior sacs to the primary bronchus via the craniomedial secondary bronchi (the most direct route), but from the posterior sacs through the tertiary bronchi and through branches of the craniomedial secondary bronchi to the primary bronchus (by-passing the most direct route, the portion of the mesobronchus posterior to the craniomedial bronchi). 4. The patterns established for panting and anaesthetized respiration were very similar to those described for resting respiration. There was no indication of an effective shunt operating during panting to avoid excessive ventilation of the exchange surfaces of the lung. 5. Flow in the tertiary bronchi appeared to be in the same direction during both inspiration and expiration (from the caudodorsal secondary bronchi towards the craniomedial secondary bronchi). Such unidirectional flow would permit the operation of a counter-current exchange system, provided that the blood vessels are arranged appropriately around the parabronchi.

The Role of the Lateral-Line Efferent System in Xenopus Laevis

Abstract: 1. Efferent impulses have been recorded from branches of lateral-line nerves. The functional significance of the efferent innervation and its action on afferent impulse activity has been examined. 2. Neither mechanical stimulation of the lateral-line receptors nor electrical stimulation of afferent nerves excites lateral-line efferent activity. 3. Trains of efferent impulses accompany all active movements for their duration. In immobilized animals a close correlation exists between impulses in lateral-line efferent nerve fibres and motor impulses in ‘large’ nerves innervating ‘twitch’ muscles, but not with impulses in nerves innervating ‘slow’ muscles. A close similarity also exists between impulse activity in different lateral-line efferent fibres. 4. Whereas electrical stimulation of ascending tracts in the spinal cord fails to excite lateral-line efferent fibres, stimulation of the spinal cord in the region of descending reticular motor axons causes efferent impulses to follow each pulse after brief, constant, latencies. It is suggested that the efferent neurones may be innervated by axon collaterals from reticular cells. 5. Electrical stimulation of efferent fibres innervating a lateral-line receptor produces transitory inhibition of impulse activity in the afferent nerve fibres. The inhibition has a long variable latency (11-30 ms) and persists for 40-60 ms. Upon cessation of inhibition, caused by a train of efferent impulses, afferent impulses reappear at an accelerated frequency (after-discharge), and quickly return to resting frequency. 6. A role of the lateral-line efferent neurones during active movement is discussed.

PHYSIOLOGY OF INSECT ECDYSIS: I. The Eclosion Behaviour of Saturniid Moths and Its Hormonal Release

Abstract: 1. In the giant silkmoths, adult eclosion is immediately preceded by a stereotyped series of abdominal movements - the pre-eclosion behaviour. The pattern of movements is species-specific and has a duration of about 1 ¼ h. 2. The pre-eclosion behaviour is followed sequentially by eclosion, the release of the labial gland secretion, the post-eclosion activity, and the spreading of the wings. These five elements of behaviour make up the emergence sequence. 3. The progression from one part of the behavioural sequence to the next is independent of stimuli provided by the pupal cuticle or cocoon, and therefore must be due to an internal programme. Thus, when the pupal cuticle was removed from pharate moths 12 h before their normal eclosion time, these ‘peeled’ animals continued to behave in a pupal fashion. But upon the arrival of the eclosion gate, the entire emergence sequence was displayed. 4. Through surgical manipulations the brain was shown to trigger the pre-eclosion behaviour. Moreover, this action of the brain was mediated by a neurosecretory hormone - the eclosion hormone. 5. Injections of extracts with eclosion-hormone activity triggered the precocious display of the emergence sequence by pharate moths. 6. When the eclosion hormone was injected into the isolated abdomens of pharate moths, these fragments performed the pre-eclosion behaviour and then shed the surrounding piece of pupal cuticle. The information for the pre-eclosion behaviour and for the abdominal movements associated with eclosion must therefore be programmed in the abdominal ganglia. Moreover, after its ‘activation’ the abdomen can switch from one behaviour pattern to the next without influence from the higher centres.

Physiological basis for detection of sound and vibration in snakes.

Abstract: 1. Snakes possess two sensory systems which respond to both air-borne sound and infstrate vibration as shown by extracellular slow evoked potentials recorded in the midbrain. One involves the VIII cranial nerve and inner ear (designated ‘auditory system’); the other requires an intact spinal cord and probably originates in skin mechanoreceptors (designated ‘somatic system’). 2. In species of the families Colubridae, Crotalidae, Boidae, the auditory system has a typical U-shaped frequency-threshold curve, similar to those found in other animals, but restricted to a narrow frequency range, c.150 Hz to 600 Hz. The U-shaped curve has a distinct minimum threshold or best frequency. Frequency-threshold curves for sound and head vibration have only minor differences. 3. The auditory system is not remarkably sensitive to sound. It is about 20 dB less sensitive than the human auditory system for air-borne sound between 200 and 400 Hz. It is remarkably sensitive to head vibration: at the best frequency, 1 A peak-to-peak amplitude is suprathreshold. 4. The auditory system responds not only to stimuli at the head but to sound and vibration delivered to the body alone. Responses to body stimulation by sound are caused by the same sensory end-organ that responds to head vibration. The role of the body in picking up sound for the auditory system can be infstantial; thus the lung plays an important part in snake hearing, a novel situation among land vertebrates. 5. The somatic system is not as sensitive to sound or to vibration as is the auditory system over most of the latter9s frequency range. The somatic system has a relatively flat frequency-threshold curve which lacks a distinct best frequency. The frequency range extends both above and below the range of the auditory system, 50-1000 Hz. The somatic system is insensitive to vibration of the head. 6. Evoked slow potentials fail to show that either spinal or auditory system distinguishes between vibratory energy from the air and from the infstrate. It is proposed that intensity information from the auditory system could be compared by the snake9s brain with intensity information from the snake9s somatic system in order to determine the relative amounts of air-borne sound and infstrate vibration in an unknown natural stimulus.

An Analysis of Pre-Flight Warm-Up in the Sphinx Moth, Manduca Sexta

Abstract: The physiology of pre-flight warm-up in Manduca sexta was analysed with regard to rate of heat production, regional partitioning of heat between thorax and abdomen, and the control of blood circulation. 1. When moths which have come to equilibrium with ambient temperature undergo pre-flight warm-up, the thoracic temperature increases linearly until flight temperature (37-39 °C) is approached. 2. The rate of increase in thoracic temperature during warm-up increases directly with ambient temperature from about 2 °C/min at 15 °C to about 7.6 °C/min at 30 °C. 3. The temperature of the abdomen remains near ambient throughout the period of warm-up, but during the initial part of post-flight cooling while thoracic temperature declines sharply abdominal temperatures rise appreciably. 4. During warm-up the rate of wing vibration increases linearly with thoracic temperature. At a thoracic temperature of 15 °C the rate is about 8/sec and at 35 °C it is about 25/sec. 5. When resting animals are held by the legs they at once begin to beat their wings through a wide angle. These wing beats at any given thoracic temperature are slower than the wing vibrations characteristic of normal warm-up, but they cause thoracic temperature to increase at almost the normal rate. 6. The removal of thoracic scales causes a decrease in rate of warm-up, but in still air this does not prevent the moths from reaching flight temperature. 7. During cooling the rate of decrease in thoracic temperature is greater in live animals than in freshly killed ones. At any given difference between thoracic and ambient temperatures cooling rates are directly related to thoracic temperature. 8. In resting moths heart pulsations are usually variable with regard to rate, amplitude, rhythm, and sometimes direction, but the records of cardiac activity simultaneously obtained from thorax and abdomen show close correspondence. 9. During warm-up the records of changes in impedance from electrodes in the abdomen indicate that pulsations of the abdominal heart are either absent, greatly reduced, or at a frequency different from that simultaneously recorded from the thorax. 10. The calculated rate of heat production during warm-up is linearly related to thoracic temperature. 11. Our data are consistent with the assumption that heat produced in the thorax during warm-up is sequestered there by reduction in blood circulation between thorax and abdomen. 12. Rates of warm-up in insects are close to the values predicted on the basis of body weight from data on heterothermic birds and animals.

The Effect of Hypoxia and Anaemia on the Swimming Performance of Rainbow Trout (Salmo Gairdneri)

Abstract: 1. A series of increasing water-velocity tests in a water tunnel has been used to investigate the maximum swimming performance of two groups of rainbow trout, one acclimated to high temperature (21-23 °C) and the other to low temperature (8-10 °C). 2. At temperatures close to their acclimation temperatures there was no significant difference between the maximum swimming speeds of the two groups of trout. 3. Exposure to an environmental oxygen tension of half the air-saturation value resulted in a 43 % reduction in maximum swimming performance at low temperature and a 30 % reduction at high temperature compared with normal animals. 4. Reduction in haematocrit to one-half or one-third normal resulted in a 34% reduction in maximum swimming speed at low temperature and a 40% reduction at high temperature compared with control animals (blank injected). 5. The results are discussed in terms of whether fish can be assumed to be in a steady state at all velocities below the critical velocity and whether it is possible to attribute the differences in performance, during anaemia and hypoxia, to increased metabolic cost of the cardiac and branchial pumps.

The Different Connections and Motor Outputs of Lateral and Medial Giant Fibres in the Crayfish

Abstract: 1. High-speed cinematography was used to analyse the abdominal movements of crayfish in response to separate stimulation of medial and lateral giant axons. These films showed that the medial giant fibres command complete abdominal flexions with little flaring of the tail appendages. The lateral giants, in contrast, evoked a relatively weak flexion of the middle abdominal segments, accompanied by promotion of the exopodites of the uropods. 2. An examination of the muscles activated by the two types of giant fibres shows that differences in the connexions between the giant fibres and specific motor neurones can account for the behavioural differences observed. 3. The output of the giant fibres was determined in the sixth abdominal ganglion, where their differential effects are most pronounced. The medial giants activate motor neurones whose axons emerge from root 6 of the sixth ganglion. The lateral giants activate motor neurones whose axons emerge via roots 2 and 3, as well as those emerging via root 6. 4. The larger motor neurones associated with the giant axons in the sixth root of the sixth ganglion have been mapped by Procion Yellow injection, and the terminations of the central giant axons in the sixth ganglion have also been determined. The connexions revealed by this technique are consistent with the physiological findings. 5. The evidence suggests that root 6 of the sixth ganglion is homologous with root 3 of the more anterior ganglia. However, the giant motor neurone of the sixth ganglion has not been identified. 6. The medial and lateral giant fibres, and perhaps other specific ‘command’ interneurones, can thus drive specific ensembles of phasic motor neurones to provide a range of stereotyped quick movements. In this respect the organization of the phasic system of interneurones and motor neurones resembles that in the tonic system.

Temperature Regulation of the Sphinx Moth, Manduca Sexta : II. Regulation of Heat Loss by Control of Blood Circulation

Abstract: 1. The circulatory anatomy of Manduca sexta is such that heat loss from the thorax is minimized when the flow of blood is reduced, and maximized when it is increased. 2. Abdominal temperatures immediately after flight suggested that blood flow was substantially increased during flight at high T A , and greatly reduced during flight at low T A . 3. When the thorax was artificially heated, the pulsation rates of the abdominal blood vessel increased, the amplitudes of the pulsations became large, and the pulsations were always in the posterior-anterior direction. 4. Heating of the abdomen often resulted in the constriction of the abdominal vessel and a reduction in the amplitude of the pulsations. 5. Transection of the ventral nerve cord reduced the frequency of the high-amplitude pulsations and abolished the ability of the abdominal heart to respond to thoracic heating. 6. When the heat was applied to the thorax, but not to the abdomen: ( a ) T Th increased while T Ab remained near T A ; ( b ) T Ab then increased while T Th stabilized near 40-42 °C; ( c ) finally, if the heat input was not excessive, T Ab also stabilized at a temperature above T A . 7. Neither stabilization of T Th nor increase of T Ab were observed during thoracic heating of dead moths or those with transected nerve chords. 8. The distribution of temperature observed in the abdomen during thoracic heating is not explicable in terms of heating by conduction from the thorax. 9. During modest thoracic heating, decreases of T Th were correlated with intervals during which there were full-length pulsations of the dorsal vessel. During periods where movement of the vessel was observed only at the anterior end of the abdomen, the temperature of the thorax increased. 10. Calculations of blood flow and heat flux indicate that the regulation of T Th in the observed range is physically reasonable by blood circulation alone.

Water flow and gas exchange at the gills of rainbow trout, Salmo gairdneri.

Abstract: 1. Ventilation volume was measured directly in rainbow trout using a rubber membrane attached to the mouth which separated inspired and expired water and allowed collection of the latter. 2. Mean ventilation volume at 8.6 °C for 18 trout weighing approximately 200 g was 37±1.8 ml/min/fish. Mean ventilation rate and ventilatory stroke volume averaged 74 breaths/min and 0.5 ml/breath respectively. 3. Ventilation volume could be increased nearly sevenfold during moderate, shortterm hypoxia as a result of a large increase in ventilatory stroke volume and a small increase in ventilation rate. 4. The ratio between the flow rates of water and blood through the gills was approximately 10. 5. Percentage utilization of oxygen from inspired water had a mean of 46±1.5% and ranged from 23 to 64%. 6. Artificial perfusion of the gills with water at different flow rates was achieved by tying a tube into the mouth of trout. 7. Perfused fish could not saturate their arterial blood with oxygen at a perfusion rate of 45 ml/min but could do so at rates ranging from 85 to 1200 ml/min. 8. Low arterial tensions at a perfusion rate approximating the mean V·G of fish with oral membranes are probably the result of a poor pattern of water flow over the gills during perfusion. 9. Opercular movements occurred only at perfusion rates below 700 ml/min and increased in frequency as perfusion rate dropped. This ventilatory activity may have resulted from receptors sensitive either to water flow over the gills or to arterial Po2. 10. As perfusion rate went up cardiac output and oxygen uptake increased. These changes were accompanied by a drop in dorsal aortic pressure which reflected vasodilation of the gills and peripheral circulation. This change in the pattern of blood flow through the gills contributed to a 50% increase in oxygen transfer factor across the gills. 11. At the highest perfusion rates there was no apparent impairment of gas exchange even though anatomical deadspace was probably high.

Gliding Flight of the White-Backed Vulture Gyps Africanus

Abstract: 1. Glide-comparison measurements were made on ten species of East African soaring birds using a Schleicher ASK-14 powered sailplane. Horizontal and vertical speed differences between bird and glider were measured by a photographic method, and used to estimate the bird9s horizontal and vertical speeds relative to the air. The analysis refers to the white-backed vulture, since by far the largest number of measurements was obtained on this species. 2. A regression analysis using a two-term approximation to the glide polar yielded an implausibly high estimate of induced drag, which was attributed to a lack of observations at lift coefficients above 0.72. An amended glide polar was constructed assuming elliptical lift distribution and a maximum lift coefficient of 1.6 to define the low-speed end, while the high-speed end was made to pass through the mean horizontal and sinking speeds of all the experimental points. This curve gave a minimum sinking speed of 0.76 m/s at a forward speed of 10 m/s, and a best glide ratio of 15.3:1 at 13 m/s. It did not differ significantly (in the statistical sense) from the original regression curve. 3. In comparing the estimated circling performance, based on the amended glide polar, with that of the ASK-14, it was concluded that the rates of sink of both should be comparable, but that the glider would require thermals with radii about 4.3 times as great as those needed to sustain the birds. The conclusions are consistent with experience of soaring in company with birds. 4. In an attempt to assess the adaptive significance of the low-aspect-ratio wings of birds specializing in thermal soaring, the white-backed vulture9s circling performance was compared with that of an ‘albatross-shaped vulture’, an imaginary creature having the same mass as a white-backed vulture, combined with the body proportions of a wandering albatross. It appears that the real white-back would be at an advantage when trying to remain airborne in thermals with radii between 14 and 17 m, but that the albatross-shaped vulture would climb faster in all wider thermals; on account of its much better maximum glide ratio, it should also achieve higher cross-country speeds. It is concluded that the wing shape seen in vultures and storks is not an adaptation to thermal soaring as such, but is more probably a compromise dictated by take-off and landing requirements. 5. The doubts recently expressed by Tucker & Parrott (1970) about the results and conclusions of Raspet (1950 a , b ; 1960) are re-inforced by the present experience.

Further Studies on Synaptic Transmission in Insects: II. Relations Between Sensory Information and its Synaptic Integration at the Level of a Single Giant Axon in the Cockroach

Abstract: 1. Some integrative properties of the chemical synapses between the sensory cereal afferent fibres and a giant axon are studied at the unitary level by external recording. 2. Unitary monosynaptic EPSPs are related to cereal receptor activity, one presynaptic spike inducing one EPSP. Unitary IPSPs are not directly related to cereal activity. They seem to originate within a ganglion. 3. Many receptors make synaptic contacts with a given giant axon. When a single receptor is strongly stimulated, the summation of elementary induced EPSPs gives a postsynaptic depolarization which is not able to reach the threshold. The simultaneous stimulation of several receptors provides a considerable amount of postsynaptic depolarization, thus triggering one or two spikes, rarely more. 4. The postsynaptic responses appear to be more or less different according to the afferent firing pattern: phasic, phasic-tonic and tonic. Some factors modulate these schemes: ( a ) Potentiation, which occurs only with phasic patterns, thus increasing their postsynaptic effect, is followed by a longer component of depression. ( b ) Limiting factors, such as fatigue phenomenon, are thought to be essentially related to depletion of an available transmitter. 5. Synchronous electrical stimulation induces a monosynaptic response, later followed by a complex polysynaptic phenomenon. These responses decrease with repetitive stimulation, but the former is far less labile than the latter. 6. These studies seem to indicate that a giant interneurone in the cockroach fires only in special conditions, namely when a strong mechanical stimulation occurs after a noticeable period of rest. This spike is then rapidly conducted to higher centres without relay.

The Body Temperature of Tenebrionid Beetles in the Namib Desert of Southern Africa

Abstract: 1. In direct sunshine the abdomen of living Onymacris brincki , which is covered by white elytra, was 3-4 °C cooler than its thorax, while in the same conditions the abdomen and thorax of O. rugatipemtis , which is an entirely black beetle, had the same temperature. Since similar effects were observed in dead beetles, the warmer thorax was not due to muscular activity. When the white elytra of brincki were covered with carbon black, its abdominal temperature rose to equal that of rugatipenntis . Models, made of pieces of black and white elytra, showed similar effects. 2. The smaller species Stenocara eburnea (with white elytra) showed a smaller and less consistent temperature depression when compared with the similar-sized species S. depressa (which is black). Abdomens of O. rugatipennis, O. laeviceps and Physosterna cribripes (all large black beetles) were from 3-5 °C wanner than O. brincki , but showed no consistent difference among themselves. 3. When O. rugatipennis was oriented head-on to the sun in its natural environment its thorax was about 4 °C cooler than when its long axis was normal to the sun9s rays. Beetles exposed to sunshine were 12-15 °C warmer than they were in the shade. When transferred from one to the other, the greater part of temperature equilibration occurred in about 2 min and equilibration was complete in about 4 min. 4. Observation suggested that beetles thermoregulate by moving between sunshine and shade. Measurements showed that a beetle exposed to alternating periods of 10 sec in sunshine and 30 sec in shade reached a steady temperature of about 33 °C, while the reverse conditions (10 sec in the shade and 30 sec in sunshine) led to a temperature of about 38 °C. In continuous alternations thoracic temperatures remained constant within about 1 °C. 5. Laboratory experiments in which the angle of incidence of the sun9s rays was varied through 180° confirmed the field results and showed that white elytra lower the abdominal temperature of living and dead beetles. 6. Upper lethal temperatures for 30 min in saturated air varied from 50 °C for the desert tenebrionid Onymacris plana to 42.5 °C for the mesic species Trigonopus capicola . In general, upper lethal temperatures correlated well with habitat and habit. 7. Making certain assumptions, analysis of the heat balance of beetles during one exposure in sunshine suggests that the difference between the white elytra of brincki and the black ones of rugatipennis as regards the amount of short-wave radiation reflected is 0.227 cal cm -2 min -1 , and further, that the reflectivities of the two surfaces are 79% and 38% respectively. 8. The selective advantage of white elytra probably has little to do with heat balance; the vivid contrast between white and black suggests that the pattern may be aposematic.

Respiratory and circulatory responses of rainbow trout larvae to carbon monoxide and to hypoxia.

Abstract: 1. Larval trout undergo a transition from cutaneous respiration to gill respiration which at 10°C is well advanced by the 18th day after hatching. 2. Resting heart rate of newly hatched trout increases during the first few days, stabilizes for a while, and then drops between the 9th and 18th day after hatching. This drop may be the result of establishment of ‘vagal tone’. 3. The basic breathing response of larval trout when hypoxic is an increase in fin movements and an increase in rate and amplitude of breathing, but breathing movements slow and weaken if environmental P O2 falls much below 40 mmHg. 4. With trout up to 8 days after hatching hypoxia causes a tachycardia. At very low P O2 levels there is a drop in heart rate and in the amount of blood pumped by the heart. Upon restoring oxygen to very hypoxic larvae, the heart rate recovers slowly, unlike the quick abolition of bradycardia of adult fish. It appears that up to the age of 8 days from hatching, trout do not have a functional bradycardia reflex associated with hypoxia. 5. The responses of larval trout to CO and to hypoxia, and of adult trout to CO, are similar in nature. It is proposed that the basic response to anoxaemia is an increase in breathing and circulation and that the adult bradycardia response to hypoxia is a superimposed mechanism which relates circulation to the quantity of oxygen presented to the gills.

The effect of environmental calcium and ovine prolactin on sodium balance in fundulus kansae

Abstract: 1. The sodium contents and rates of turnover of sodium have been determined in both intact and hypophysectomized Fundulus kansae in a variety of media. 2. A reduction of the calcium content of fresh water from 1.0 to 0.1 mM/l increased the rate of sodium efflux by half while transter to calcium-free water increased the rate several fold. 3. The rate of sodium efflux increased fourfold in sea water containing no magnesium and only 1 mm/l calcium. 4. Hypophysectomy increased the rate of efflux in fresh water but reduced it in sea water. 5. Intact fish adapted to sea water and treated with prolactin showed a net gain of sodium probably due to a reduction in the activity of the sodium efflux pump. 6. Both intact and hypophysectomized fish on transfer from sea water to fresh water reduced the rate of efflux of sodium in a series of stages. 7. Studies of the rate of efflux of sodium before and after transfer between various media showed no evidence of exchange diffusion or of a linked sodium-potassium efflux pump, but did show evidence or interaction between sodium and chloride fluxes probably as a consequence of potential changes. 8. The rate of efflux of sodium from F. kansae doubled following hypophysectomy. The ability of hypophysectomized F. kansae to survive in fresh water after hypophysectomy, unlike F. heteroclitus , is due to a more effective uptake system.

The Pharmacology of Efferent Synapses in the Lateral-Line System of Xenopus Laevis

Abstract: 1. The nature of the transmitter substance released at the lateral-line efferent synapses was investigated by histochemical techniques in Xenopus and Acerina and by pharmacological methods in Xenopus . 2. The bases of lateral-line hair-cells and fine fibres in the lateral-line nerves reacted positively for acetylcholinesterase in Acerina and to a lesser extent in Xenopus . 3. Acetylcholine (10-6M, and acetyl-β-methyl choline (5 x 10-6M), which has a muscarinic action, caused strong reversible inhibition of afferent impulses when pipetted on to the undersides of lateral-line stitches. Carbachol (5 x 10-4 to 5 x 10-5M) caused a smaller reversible inhibition of spontaneous afferent impulses, but other nicotinic substances (propionylcholine and buterylcholine) had no effect. 4. Physostigmine (5 x 10-5M) prolonged inhibition of afferent impulses by electrical stimulation of efferent fibres, but atropine (5 x 10-6M) blocked it. 5. Calcium and magnesium interact at the efferent synapses in a way similar to that found at the amphibian neuromuscular junction. 6. Arguments are put forward to support the hypothesis that acetylcholine is released at lateral-line efferent synapses.

Calcium regulation in the freshwater mollusc, Limnaea stagnalis (L.) (Gastropoda: Pulmonata). I. The effect of internal and external calcium concentration.

Abstract: 1. Calcium regulation in normal and calcium-depleted snails has been investigated. 2. L. stagnalis has an uptake mechanism with a high affinity for calcium ions and shows a positive calcium balance in media containing more than 0.062 mM Ca/l. 3. Influx and net uptake of calcium are related to external calcium concentration in a non-linear manner. The uptake mechanism is half-saturated and near-saturated in external media containing 0.3 and 1.0-1.5 mM Ca/l respectively. 4. Calcium uptake from external concentrations of less than 0.5 mM Ca/l is against a small electrochemical gradient whereas from external concentrations greater than 0.5 mM Ca/l there is no adverse gradient. 5. Calcium depletion does not significantly alter the normal influx or net uptake rate of calcium from 1.0 mM Ca/l. 6. The calcium concentration in the blood remains constant during net uptake from, and net loss to, the medium. 7. A comparison is made between the mechanisms of sodium regulation and calcium regulation in L. stagnalis .

Variable Responsiveness of a Visual Interneurone in the Free-Moving Locust, and its Relation to Behaviour and Arousal

Abstract: 1. Recorded from a dissected immobilized animal, or from an unrestrained animal which is quiescent, the descending contralateral movement detector (DCMD) neurone shows an exponential decremental response to a repetitive stimulus (habituation), reaching a plateau level characteristic of the stimulus conditions. The process is site-specific on the retina, and movement to a new area of retina gives a complete recovery. In the absence of stimulation responsiveness returns over minutes or hours. 2. Immediate recovery without a rest (dishabituation) can be obtained by a variety of strong sensory stimuli of several different modalities (‘extra-stimuli’) or by non specific electrical stimulation of parts of the CNS. The dishabituating efficacy of all these wanes with repetition. When the habituating stimulus is moved to a new retinal site the previous site is not dishabituated. 3. Dishabituation is not site-specific but affects the whole retina simultaneously. It appears to reverse the original decremental process (‘re-set’) rather than to produce an independent enhancement elsewhere in the pathway, as it does not increase the response from a submaximally stimulated, but unhabituated, retinal site. 4. In unrestrained animals dishabituating extra-stimuli also cause behavioural arousal or other motor activity. When motor activity starts, the DCMD is dishabituated and shows no regular decremental trend thereafter until movement ceases. DCMD background activity is also increased. These effects are not due to the visual stimulus of the moving appendages. 5. The association between motor activity and dishabituation suggests that the latter derives either from motor system collaterals or from mechanoreceptive reafference. Stimulation of the antennal nerve of a totally de-efferented brain cause some dishabituation; this eliminates the lower motor system (below command-fibre level) as the source of dishabituation and suggests it is purely sensory. 6. The activity of a thoracic cord unit (of possibly a wide-field mechanoreceptor interneurone) precedes by 5-20 sec, and closely correlates with, changes in responsiveness of the DCMD. It is either an important input to, or an output from, the dishabituating system. 7. Progressive reduction of sensory input to the brain affects DCMD responsiveness as follows: (i) spontaneous dishabituation is less frequent, (ii) dishabituation is less easily induced and smaller, (iii) rate of habituation is increased, (iv) plateau response level after habituation is lower. 8. Electrical stimulation of the circumoesophageal connective can depress DCMD responsiveness for many minutes. 9. The probable anatomical and physiological bases for modulation of DCMD responsiveness are discussed.

Gas Exchange with Air and Water in an Air-Breathing Catfish, Saccobranchus (≡Heteropneustes) Fossilis

Abstract: 1. Gas exchange of Saccobranchus fossilis with water and air has been studied under various experimental conditions which were designed to simulate some of the conditions of tropical Asia. 2. In tap water the fish exchanges gases with both water and air. When kept in air-saturated water it can exchange gases with water alone for periods of 6-12 h or even more. In de-oxygenated water, with free access to air, it obtains oxygen from the air and can live for several days under these conditions. 3. In air-saturated water more oxygen is obtained from water (60%) than from air (40%), but in hypoxic water this ratio is reversed. 4. When the fish is submerged in water, free access to air being prevented, the oxygen consumption is reduced, even in air-saturated water. In hypoxic and hypercarbic water oxygen consumption is further reduced. In air-saturated water about 17% of the oxygen enters via the skin and the rest via the gills. When exchanging gases with water alone and subjected to a gradual hypoxia, the fish shows a less dependent respirator. 5. When the fish is removed from the water its oxygen consumption is reduced. A greater reduction occurs when the fish is kept in de-oxygenated water but allowed to breathe air. 6. When the fish is exchanging gases with both water and air very little carbon dioxide is released into the air (RQ = 0·17). The total RQ in fish removed from the water is low, i.e. 0·58. The fish can survive in hypercarbic water only, provided that the content of carbon dioxide does not exceed 14·5 volumes %, when surfacing becomes necessary.