On the invariance of visual stimulus efficacy with respect to variable spatial positions

Summary In the fly,Calliphora erythrocephala, visual stimuli presented in an asymmetrical position with respect to the fly elicit roll or tilt movements of the head by which its dorsal part is moved towards the light areas of the surroundings (Figs. 4–7). The influence of passive body roll and tilt (gravitational stimulus) on the amplitude of these active head movements was investigated for two types of visual stimuli: (1) a dark hollow hemisphere presented in different parts of the fly's visual field, and (2) a moving striped pattern stimulating the lateral parts of one eye only.The response characteristics of the flies in the bimodal situation in which the gravitational stimulus was paired with stimulation by the dark hollow hemisphere can be completely described by the addition of the response characteristics for both unimodal situations, i.e. by the gravity-induced and visually induced characteristics (Figs. 8, 9). Therefore, the stimulus efficacy of the dark hollow hemisphere is independent of (=invariant with respect to) the flies' spatial position. The advantage of this type of interaction between gravity and visual stimulation for the control of body posture near the horizontal is discussed.In contrast, the efficacy of moving patterns depends on (=non-invariant with respect to) the spatial position of the walking fly. Regressive pattern movements exhibit their stronger efficacy with respect to progressive ones only when the gravity receptor system of the legs is stimulated. The stronger efficacy of downward vs upward movements can only be demonstrated when the flies are walking horizontally, independently of whether the leg gravity receptor system is stimulated by gravity or not (Fig. 10).The results are discussed with respect (1) to the invariance and non-invariance of the efficacy of visual stimuli with respect to the direction of the field of gravity, (2) to the formation of reference lines by the gravitational field which are used by the walking fly to determine the orientation of visual patterns, and (3) to the possible location of the underlying convergence between gravitationally and visually evoked excitation. As all types of head responses occur only in walking flies, we also discussed the possible influences of some physiological processes like arousal, proprioceptive feedback during walking and various peripheral sensory inputs on the performance of behavioural responses in the fly (Fig. 11).     

Hydrodynamic orientation of crayfish (Procambarus clarkii) to swimming fish prey

Reversibly blindfolded crayfish (Procambarus clarkii) react to small swimming fish (Astyanax fasciatus mexicanus) approaching or passing nearby with antennal and cheliped movements and body turns (Fig. 3). We studied the accuracy and dynamics of crayfish orientation responses to the previously analyzed hydrodynamic disturbances caused by the fish, mostly produced by tail flicks.Antennal and cheliped movements started slightly before the onset of turning responses (Fig. 4). Antennal sweeps were performed most rapidly. 50% of the appendage sweeps resulted in contacts with the fish (Fig. 5).Most turns were directed toward the stimulus (Fig. 6). Response amplitudes increased with increasing stimulus angle. Turns were accurate for small stimulus angles, but smaller than expected for larger ones. Sweeps of ipsilateral antennae and chelipeds were generally directed backwards, while those of contralateral appendages were smaller and directed forwards. The amplitudes of appendage sweeps first increased with increasing stimulus angle and then decreased again for more caudal stimulus directions. Lateral stimuli (60°–120°) from opposite sides were usually significantly distinguished. The amplitudes of the different elements of orientation behaviour were highly correlated with each other, indicating that they were directed by the same sensory input.     

Über das Formunterscheidungsvermögen der Schmeißfliege Calliphora erythrocephala

Zusammenfassung Mit Alternativwahlversuchen wird nachgewiesen, daß folgende Formmerkmale die Zielorientierung (= Telotaxis) von laufenden, männlichen Schmeißfliegen (Calliphora erythrocephala) stimulieren: 1. Dunkle Kontrastflächen (Abb. 1); 2. Vertikale Kontrastgrenzen (Abb. 2-6); 3. Figurengliederung (Abb. 3f und 4).

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On the pattern discrimination of the blow fly Calliphora erythrocephala

Summary Experiments on binary choices of walking male blow flies (Calliphora erythrocephala) demonstrate the stimulatory value of the following pattern characteristics on the targed orientation (= telotaxis): 1. Dark contrasting area (Fig. 1). 2. Vertical edge of contrast (Fig. 2–6). 3. Disruption of shape (Fig. 3f and 4).

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Mit Unterstützung der Deutschen Forschungsgemeinschaft (SFB 45).     

The three-dimensional optomotor torque system ofDrosophila melanogaster

Summary The well known optomotor yaw torque response in flies is part of a 3-dimensional system. Optomotor responses around the longitudinal and transversal body axes (roll and pitch) with strinkingly similar properties to the optomotor yaw response are described here forDrosophila melanogaster. Stimulated by visual motion from a striped drum rotating around an axis aligned with the measuring axis, a fly responds with torque of the same polarity as that of the rotation of the pattern. In this stimulus situation the optomotor responses for yaw, pitch and roll torque have about the same amplitudes and dynamic properties (Fig. 2). Pronounced negative responses are measured with periodic gratings of low pattern wavelengths due to geometrical interference (Fig. 3). The responses depend upon the contrast frequency rather than the angular velocity of the pattern (Fig. 4). Like the optomotor yaw response, roll and pitch responses can be elicited by small field motion in most parts of the visual field; only for motion below and behind the fly roll and pitch responses have low sensitivity.The mutantoptomotor-blind ^H31 (omb ^H31) in which the giant neurones of the lobula plate are missing or severely reduced, is impaired in all 3 optomotor torque responses (Fig. 5) whereas other visual responses like the optomotor lift/thrust response and the landing response (elicited by horizontal front-to-back motion) are not affected (Heisenberg et al. 1978).We propose that the lobula plate giant neurons mediate optomotor torque responses and that the VS-cells in particular are involved in roll and pitch but not in lift/thrust control. This hypothesis accommodates various electrophysiological and anatomical observations about these neurons in large flies.Abbreviation EMD elementary movement detector     

A comparison of the responses of tropical and temperate flies (Diptera: Sarcophagidae) to cold and heat stress

Summary Two flesh fly species from the tropical lowlands (Peckia abnormis and Sarcodexia sternodontis) were more susceptible to both cold-shock and heatshock injury than temperate flies (Sarcophaga crassipalpis and S. bullata) and a fly from a tropical high altitude (Blaesoxipha plinthopyga). A brief (2-h) exposure to 0°C elicits a protective response against subsequent cold injury at–10°C in the temperate flies and in B. plinthopyga but no such response was found in the flies from the tropical lowlands. However, both tropical and temperate flies could be protected against heat injury (45°C) by first exposing them to a mild heat shock (2 h at 40°C). The supercooling point is not a good indicator of cold tolerance: supercooling points of pupae were similar in all species, ranging from–18.9 to–23.0°C, and no differences were found between the tropical and temperate species. Among the temperate species, glycerol, the major cryoprotectant, can be elevated by short-term exposure to 0°C, but glycerol could not be detected in the tropical flies. Low-temperature (0°C) exposure also increased hemolymph osmolality of the temperate species, but no such increase was observed in the tropical lowland species. Adaptations to temperature stress thus differ in tropical and temperate flesh flies: while flies from both geographic areas share a mechanism for rapidly increasing heat tolerance, only the temperate flies appear capable of responding rapidly to cold stress. The presence of a heat shock response in species that lack the ability to rapidly respond to cold stress indicates that the biochemical and physiological bases for these two responses are likely to differ.     

Responses and song pattern copying of Omega-type I-neurons in the cricket,Gryllus bimaculatus,at different prothoracic temperatures

Summary Omega-type I-neurons (ON/1) (Fig. 1A) were recorded intracellularly with the prothoracic ganglion kept at temperatures of either 8–9°, or 20–22° or 30–33 °C and the forelegs with the tympanal organs kept at ambient temperature (20–22 °C). The neurons were stimulated with synthetic calling songs (5 kHz carrier frequency) with syllable periods (SP in ms) varying between 20 and 100, presented at sound intensities between 40 and 80 dB SPL. The amplitude and duration of spikes as well as response latency decreased at higher temperatures (Figs. 1 B, 2, 6). At lower prothoracic temperatures (8–9 °C) the neuron's responses to songs with short SP (20 ms) failed to copy single syllables, or with moderate SP (40 ms) copied the syllable with low signal to noise ratio (Fig. 3). The auditory threshold of the ON/1 type neuron, when tested with the song model, was temperature-dependent. At 9° and 20 °C it was between 40 and 50 dB SPL and at 33 °C it was less than 40 dB SPL (Fig. 4). For each SP, the slope of the intensity-response function was positively correlated with temperature, however, at low prothoracic temperatures the slope was lower for songs with shorter SPs (Fig. 5). The poor copying of the syllabic structure of the songs with short SPs at low prothoracic temperatures finds a behavioral correlate because females when tested for phonotaxis on a walking compensator responded best to songs with longer SPs at a similar temperature.Abbreviations epsps excitatory postsynaptic potentials - ON/1 omega-type I-neuron - SP syllable period - SPL sound pressure level     

Saccadic head and thorax movements in freely walking blowflies

Visual information processing is adapted to the statistics of natural visual stimuli, and these statistics depend to a large extent on the movements of an animal itself. To investigate such movements in freely walking blowflies, we measured the orientation and position of their head and thorax, with high spatial and temporal accuracy. Experiments were performed on Calliphora vicina, Lucilia cuprina and L. caesar. We found that thorax and head orientation of walking flies is typically different from the direction of walking, with differences of 45° common. During walking, the head and the thorax turn abruptly, with a frequency of 5–10 Hz and angular velocities in the order of 1,000°/s. These saccades are stereotyped: head and thorax start simultaneously, with the head turning faster, and finishing its turn before the thorax. The changes in position during walking are saccade-like as well, occurring synchronously, but on average slightly after the orientation saccades. Between orientation saccades the angular velocities are low and the head is held more stable than the thorax. We argue that the strategy of turning by saccades improves the performance of the visual system of blowflies.     

Learning and discrimination of coloured papers in the walking blowfly,Lucilia cuprina

Summary A new training and testing paradigm for walking sheep blowflies, Lucilia cuprina, is described. A fly is trained by presenting it with a droplet of sugar solution on a patch of coloured paper. After having consumed the sugar droplet, the fly starts a systematic search. While searching, it is confronted with an array of colour marks consisting of four colours displayed on the test cardboard (Fig. 1). Colours used for training and test include blue, green, yellow, orange, red, white and black.Before training, naive flies are tested for their spontaneous colour preferences on the test array. Yellow is visited most frequently, green least frequently (Table 2). Spontaneous colour preferences do not simply depend on subjective brightness (Table 1).The flies trained to one of the colours prefer this colour significantly (Figs. 5 and 9–11). This behaviour reflects true learning rather than sensitisation (Figs. 6–7). The blue and yellow marks are learned easily and discriminated well (Figs. 5, 9, 11). White is also discriminated well, although the response frequencies are lower than to blue and yellow (Fig. 11). Green is discriminated from blue but weakly from yellow and orange (Figs. 5, 9, 10). Red is a stimulus as weak as black (Figs. 8, 9). These features of colour discrimination reflect the spectral loci of colours in the colour triangle (Fig. 14).The coloured papers seem to be discriminated mainly by the hue of colours (Fig. 12), but brightness may also be used to discriminate colour stimuli (Fig. 13).     

Simulations of a model for transmitter kinetics

The influence of the internal water balance on the phototactic behaviour in the walking female fly (Calliphora erythrocephala Meig.) was investigated. The phototactic reaction depends on the age of the flies and the duration of water withdrawal. In young blowflies with progressive dehydration, the strength of the light reaction varies considerably from fly to fly. From the 4th. day of life onwards up to day 21 the flies respond much more homogeneously and elicit a reproduceable temporal pattern of reaction (Figs. 2 and 3). All the following statements refer to the behaviour of 10-day-old, virgin females, which, under optimal humidity conditions, have been shown to be spontancously photonegative (Meyer, 1978). The phototactic reaction of progressively dehydrated flies depends in a characteristic manner on the illumination conditions during the intervals between tests. If the flies are kept in darkness during these intervals, the light reaction varies rhythmically, with a period of almost exactly 12 h (Figs. 4a and 5). Under the test conditions this rhythm is found not to vary with the time of day (Fig.4a), or with the length of the between-test intervals, for intervals up to 4h long (Fig. 6). If the flies are kept under illumination during the intervals between tests, the light reaction becomes arhythmical. After an initial maximum after 2–4h of dehydration, further photopositive responses are severely suppressed (Fig. 4b). When the ocelli are covered, the between-test illumination no longer influences the mean response to light. The arhythmic dehydrationtime vs. light-reaction curve in this case is characterised by a strong sustained enhancement of runs towards the light after 10h of dehydration (Fig. 7). A preliminary model of a possible control system for this moisture-dependent phototactic switching is presented, from which all essential results can be deduced. This system determines the phototactic turning direction from the ocelli afferences. These afferences act upon the central nervous system in two ways: directly and also indirectly via the internal water regulation.This work was supported by the DFG-(Me417/4)     

Kinematic diversity suggests expanded roles for fly halteres

The halteres of flies are mechanosensory organs that provide information about body rotations during flight. We measured haltere movements in a range of fly taxa during free walking and tethered flight. We find a diversity of wing–haltere phase relationships in flight, with higher variability in more ancient families and less in more derived families. Diverse haltere movements were observed during free walking and were correlated with phylogeny. We predicted that haltere removal might decrease behavioural performance in those flies that move them during walking and provide evidence that this is the case. Our comparative approach reveals previously unknown diversity in haltere movements and opens the possibility of multiple functional roles for halteres in different fly behaviours.     

The role of retinula cell types in fixation behaviour of walkingDrosophila melanogaster

Summary Fixation behaviour of free walking wild typeDrosophila and various retinal mutants was tested in a circular arena. Optomotor response was also measured as a test of the function of R1-6.ora andsev,ora do not fixate a narrow stripe (10° or 20°, Fig. 1) but are able to orient towards broad stripes (110° or 180°, Fig. 1). The behaviour ofsev is not different from wild type. Fixation behaviour ofw rdgB is similar toora (Figs. 5, 6). The mutantora has a maximum optomotor response at low contrast frequencies (Fig. 2), but the threshold for this response is at least one log unit higher than in wild type orsev (Fig. 8). The light intensity threshold at 550 nm of fixation to a broad stripe (110°) is 1–2 log units higher inora than in wildtype, and 4 log units higher insev,ora and the structural brain mutantVam (Fig. 7).The conclusions are that retinula cells R1-6 mediate fixation to a narrow stripe at high and low ambient light intensities, and to a broad stripe at low ambient light levels. R8, possibly in conjunction with R1-6, contributes to orientation towards broad stripes at high light intensities. This hypothesis is supported by evidence that blue-adapted white-eyed flies are able to orient towards a broad stripe at high blue light intensities (Figs. 9 and 12). Blue adaptation totally eliminates the optomotor response (Figs. 10, 11) and so the optomotor response observed inora at low contrast frequencies (Figs. 2 and 8) is most likely due to the small remnants of the rhabdomeres of R1-6 that remain.Abbreviations PDA prolonged depolarising afterpotential - ERG electroretinogram     

Directionality of antennal sweeps elicited by water jet stimulation of the tailfan in the crayfish Procambarus clarkii

Summary Directionality and intensity dependence of antennal sweeps elicited by water jet stimulation of the tailfan in tethered, reversibly blinded adult and juvenile crayfish (Procambarus clarkii) were analyzed.Resting crayfish keep their antennae at about 50° symmetrically to the longitudinal body axis (Figs. 2 bottom, and 3).In adults, tailfan stimulation elicits synchronous backward sweeps of both antennae, which increase for more caudal stimulus directions (Figs. 2–4 and 5A). Directions differing by 30°–60° are significantly distinguished (Fig. 4). The mean sweep of the ipsilateral antenna significantly overrides that of the contralateral antenna for rostrolateral stimulation at 40–200 mm/s stimulus velocity and lateral to caudolateral stimulation at 40 mm/s and thus lateralization of the stimulus is revealed (Figs. 2 top, 4 and 5A). Mean antennal sweeps at a given stimulus direction and distance increase with increasing stimulus velocity (40–250 mm/s, Fig. 5A).In juveniles, the directional dependence of antennal sweeps is reduced compared to that of adults, while a similar intensity dependence is found (Fig. 5B).The pronounced directionality of the antennal response in adult crayfish vanishes and response latencies increase after reversibly covering the tailfan with a small bag or the telson with waterproof paste (Figs. 6 and 7). Thus, tailfan and especially telson mechanoreceptors play an important role in the localization of water movements elicited by predators or prey behind the crayfish.     

What kind of movement detector is triggering the landing response of the housefly?

As shown before, the latency of the housefly's landing response depends on the conditions of the visual stimulus (Borst 1986). Accordingly, the latency can be used to characterize the movement detection system which is triggering the landing response.The stimulus was a sinusoidal periodic pattern of vertical stripes presented bilaterally in the frontolateral eye region of the fly. It started to move, simultaneously on either side, from front to back at a given time. The latency of the response was measured by means of an infrared light-beam that was interrupted whenever the fly lifted its forelegs to assume a preprogrammed landing posture (Fig. 1). The latency was found to vary in a range from 60 ms up to several seconds depending on the pattern's spatial wavelength , contrast frequency cf and contrast C.For sufficiently high pattern contrast the optimum of the reaction (minimum latency) is found at spatial wavelengths of 30–40° and contrast frequencies of 8–17 periods/s (Fig. 3a). This is about 2–10 times more than is anticipated from the optomotor response under similar conditions. Evaluation of the optimum contrast frequency cf _OPT at different wavelengths shows that cf _OPT is not independent of (Fig. 3b, solid line). The same is true for the contrast dependence of the reaction: reduction of the contrast leads not only to a general decrease in the response amplitudes (prolongation of the latency) (Fig. 4a), but also to a shift of cf _OPT towards lower contrast frequencies (Fig. 4b, solid line).In the theory of the correlation-type movement detector (Reichardt 1961) which underlies the optomotor response of flies the dependence of cf _OPT on pattern wavelength and/or pattern contrast is not expected under stationary conditions. However, as shown by computer simulation all experimental results can be explained by a homogeneous retinotopic array of correlation movement detectors (Fig. 2) if their response under non-stationary conditions is taken into account. We simply assume that the spatially and temporally integrated output of the movement detectors is evaluated by a threshold device (Fig.5). The correlation-type movement detection in combination with a temporal integrator system predicts the rather complex dependence of the optimum contrast frequency on pattern wavelength and pattern contrast (dashed lines in Fig. 3b and 4b) and provides the missing explanation of the variable latencies of the landing response.Comparing the parameters of the correlation-type movement detector derived in the present study with those of the optomotor response, the landing response seems to use the same type of movement detection system. To account for the high wavelength optimum, however, the input elements of the movement detection system of the landing response might have an increased visual field (e.g. by pooling neighbouring visual elements) and, accordingly, a reduced visual acuity as compared with the input elements of the optomotor system.Abbreviations (°) spatial pattern wavelength - w(°/s) angular velocity of the pattern - cf (Hz) contrast frequency=w/ - cf _OPT(Hz) cf leading to the shortest latency - (Hz) angular frequency=2cf - I mean luminance of the pattern - I modulation amplitude of the pattern - C pattern contrast=I/ - (ms) time constant of a filter - (°) angle between the optical axis of neighbouring visual elements - (°) acceptance angle of visual elements     

Attractants for the gravid Queensland fruit fly Dacus tryoni

The vapours of certain pure chemicals, typical of ripe fruits, elicited characteristic components of ovipositional behaviour from gravid Dacus tryoni (Froggat) in an olfactometer: the flies walked and flew upwind to the source of the vapour and then probed with their ovipositors. A range of alcohols, acids, ketones and esters having 2–6 carbon atoms were effective (1 and 10% of iso-butyric acid, n-butyric acid, methyl butyrate, ethyl butyrate, 2-butanone, ethyl lactate and ethyl acetate; and 10% concentrations of ethanol and 2-propanone). The most effective were 4–6 carbon acids, esters and ketones. Behavioural threshold for n-butyric acid vapour at 26°C was obtained from a 5×10^–3% dilution in paraffin oil; maximum fly response occurred at about 200 times this concentration. Low concentrations of the 15-carbon sesquiterpene, -farnesene, were also very effective, despite its lower volatility. These results suggest that at least three different types of alfactory sensory neurones are involved in the identification of fruit attractants by gravid D. tryoni.     

Is the landing response of the housefly (Musca) driven by motion of a flow field?

The landing response of tethered flying housefliesMusca domestica elicited by motion of periodic gratings is analysed. The field of view of the compound eyes of a fly can be subdivided into a region of binocular overlap and a monocular region. In the monocular region the landing response is elicited by motion from front to back and suppressed by motion from back to front. The sensitivity to front to back motion in monocular flies (one eye covered with black paint) has a maximum at an angle 60°–80° laterally from the direction of flight in the equatorial plane. The maximum of the landing response to front to back motion as a function of the contrast frequencyw/ is observed at around 8 Hz. In the region of binocular overlap of monocular flies the landing response can be elicited by back to front motion around the equatorial plane if a laterally positioned pattern is simulataneously moved from front to back. 40° above the equatorial plane in the binocular region the landing response in binocular flies is elicited by upward motion, 40° below the equatorial plane in the binocular region it is elicited by downward motion. The results are interpreted as an adaptation of the visual system of the fly to the perception of a flow field having its pole in the direction of flight.     

Identified nonspiking interneurons in leg reflexes and during walking in the stick insect

In the stick insect Carausius morosus identified nonspiking interneurons (type E4) were investigated in the mesothoracic ganglion during intraand intersegmental reflexes and during searching and walking.In the standing and in the actively moving animal interneurons of type E4 drive the excitatory extensor tibiae motoneurons, up to four excitatory protractor coxae motoneurons, and the common inhibitor 1 motoneuron (Figs. 1–4).In the standing animal a depolarization of this type of interneuron is induced by tactile stimuli to the tarsi of the ipsilateral front, middle and hind legs (Fig. 5). This response precedes and accompanies the observed activation of the affected middle leg motoneurons. The same is true when compensatory leg placement reflexes are elicited by tactile stimuli given to the tarsi of the legs (Fig. 6).During forward walking the membrane potential of interneurons of type E4 is strongly modulated in the step-cycle (Figs.8–10). The peak depolarization occurs at the transition from stance to swing. The oscillations in membrane potential are correlated with the activity profile of the extensor motoneurons and the common inhibitor 1 (Fig. 9).The described properties of interneuron type E4 in the actively behaving animal show that these interneurons are involved in the organization and coordination of the motor output of the proximal leg joints during reflex movements and during walking.Abbreviations CLP reflex, compensatory leg placement reflex - CI1 common inhibitor I motoneuron - fCO femoral chordotonal organ - FETi fast extensor tibiae motoneuron - FT femur-tibia - SETi slow extensor tibiae motoneuron     

Elementary detectors for vertical movement in the visual system of Drosophila

Optomotor thrust responses of the fruitfly Drosophila melanogaster to moving gratings have been analysed in order to determine the arrangement of elementary movement detectors in the hexagonal array of the compound eye. These detectors enable the fly to perceive vertical movement. The results indicate that, under photopic stimulation of a lateral equatorial eye region, the movement specific response originates predominantly from two types of elementary movement detectors which connect neighbouring visual elements in the compound eye. One of the detectors is oriented vertically, the other detector deviates 60° towards the anterior-superior direction (Fig. 5b). The maximum of the thrust differences to antagonistic movement is obtained if the pattern is moving vertically or along a superior/anterior — inferior/posterior direction 30° displaced from the vertical (Fig. 3d,e, Fig. 6). Only one of the detectors coincides with one of the two detectors responsible for horizontal movement detection. This indicates that a third movement specific interaction in the compound eye of Drosophila has to be postulated. — The contrast dependence of the thrust response (Fig. 2) yields the acceptance angle of the receptors mediating the response. The result coincides with the acceptance angle found by analysis of the turning response of Drosophila (Heisenberg and Buchner, 1977). This value corresponds to the acceptance angle expected, on the basis of optical considerations, for the receptor system R 1–6. — The movement-specific neuronal network responsible for thrust control is not homogeneous throughout the visual field of Drosophila. Magnitude and preferred direction of the thrust response in the upper frontal part of the visual field seem to vary considerably in different flies (Fig. 6).     

Response characteristics of cold cell on the antenna ofLocusta migratoria L.

Summary The dendritic outer segment of the cell which is most likely the cold unit in the poreless coeloconic sensilla onLocusta migratoria antennae, has finger-like projections up to 1.5 m long and 0.13 m thick (Fig. 1). This unit responds to constant temperature, to slowly changing temperature and to step changes. Under stationary conditions impulse frequency attained 35 imp/s. Between 14 °C and 41 °C the higher frequencies were associated with the higher temperatures (Fig. 5). In this range the differential sensitivity is positive but not large: + 0.8 (imp/s)/°C. Its resolving power for steady temperature is 4.7 °C.Downward step changes produced by shifting between airstreams at different temperatures yield far higher frequencies (Figs. 2, 3). Step amplitudes were between –0.1 °C and –12 °C; the conditioning temperature from which the steps were initiated, was between 16 °C and 33 °C. Frequency peaked during the first 50 ms after stimulus onset (Fig. 2) and reached its highest values (310–340 imp/s) at initial temperatures above 30 °C and steps larger than –10 °C (Fig. 4). The mean differential sensitivity from 23 curves was –19 (imp/s)/°C and the resolving power 0.6 °C.During slowly changing temperature the impulse frequency was governed by two parameters simultaneously: ambient temperature and its rate of change. Rates were between 0.001 °C/s or less, and 0.03 °C/s in either direction. Frequency was higher during slow cooling at a given temperature than during slow warming (Fig. 6). The average differential sensitivity to the rate of change was –210 (imp/s)/(°C/s). Further, the larger responses to cooling developed at lower ambient temperatures (differential sensitivity: –1.0 (imp/s)/°C). It is to be noted that this sign is negative, in contrast to the sign for differential sensitivity to constant temperature and also for the influence of initial temperature on the response to downward step changes.Abbreviations b Slope of characteristic curve, differential sensitivity - F impulse frequency in imp/s - imp/s impulses/s - P _w partial pressure of water vapor in torr - r correlation coefficient - T temperature in °C - T T-step - x resolving power in °C     

Movement sensitivities of cells in the fly's medulla

Summary Intracellular recordings were made in the medullae of intact, restrained females ofCalliphora vicina that faced a hemispherical, minimum-distortion surface upon which moving patterns and spots were projected from the rear (Fig. 2). In the distal medulla, noisy hyperpolarizations to light, most likely recorded in terminals of laminar (L) cells, had flicker-like oscillations to moving gratings of 15° spatial wavelength but not of 2.5° spatial wavelength (Fig. 3). Medullary (M) cells penetrated distally responded to grating movements with similar but depolarizing oscillations, in one cell 180° out of phase with a nearby laminar response (Figs. 4–6).A characteristic movement response recorded from most medullary cells consisted of abrupt, maintained nondirectional depolarizations in response to movements of gratings, often with directional ripple or spikes superimposed. When directions of movement reversed, there were brief repolarizations, but when movements stopped, depolarizations decayed away more slowly (Figs. 7 and 8). Magnitude of responses increased with increasing speeds of both 15° and 2.5° gratings (Figs. 9–11). In some cells, there were delayed decays of responses after stopping (Fig. 12). Still other cells seemed to receive inhibition from other, characteristically responding cells (Fig. 13).Receptive fields tested were simple and usually large, with only a suggestion of surround inhibition (Fig. 14). In general, intensity and position were interchangeable over a cell's receptive field (Figs. 15 and 16). Moving edges and dark spots elicited responses primarily within receptive field centers (Figs. 18–20).It is argued that waveforms of characteristic movement responses can be explained by multiplicative inputs from L- and M-cells to movement detectors (Figs. 21–26).Abbreviations L cells laminar (monopolar) cells - M cells medullary cells     

Thoracic temperature,shivering, and flight in the monarch butterfly,Danaus plexippus (L.)

Summary Monarch butterflies, Danaus plexippus (L.), display a warm-up behavior characterized by wingstrokes of small amplitude. Thoracic temperature during this shivering and during fixed flight was measured by means of a smallbead thermistor inserted into the thorax. At ambient temperatures of 15–16°C, once shivering is initiated the thoracic temperature rises at a maximum rate of 1.3°C/min, and a thoracic temperature 4.0°C greater then ambient is produced (Table 1). Fixed flight at these low ambient temperatures results in a similar rate of increase in thoracic temperature, and a similar temperature excess is produced (Fig. 3). At ambient temperatures between 22 and 35°C the thoracic temperature of an animal starting to fly rises at a faster rate, 3.6°C/min, and reaches a greater excess, 7.9°C (Fig. 4). The wingbeat frequency of animals in fixed flight increases with increasing thoracic temperature (Fig. 2). In the absence of direct solar radiation, shivering typically occurs prior to flight at low ambient temperatures (13–17°C), and the resulting increase in thoracic temperature allows monarch butterflies to fly at these cool temperatures.I thank Miss Janice Ruppert and Mr. C. J. Doughty for their valuable technical assistance. The co-operation of the administrators of New Brighton Beach State Park in permitting me to collect in the park is appreciated. Financial support for this study was provided in part by a faculty research grant from the University of California.