bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiology of Insect Ecdysis
Authors: Truman James W.
Published: April 2021

At the end of the last larval instar the mature silkworm larva stops feeding and spins a silken cocoon. In this chamber the animal subsequently pupates and in some cases overwinters in a dormant condition-termed diapause. Under the influence of the warmth and lengthening days of spring, the pupa terminates diapause and initiates adult development. Weeks later the mature moth sheds the pupal exuviae and escapes from the cocoon. In Cecropia (Hyalophora cecropia) and many other saturniids the larva has prepared for this eventuality by spinning into the cocoon an ‘escape-hatch’ or valve through which the moth emerges (Van der Kloot & Williams, 1953). Among the silkworms of the genus Antheraea the moth resorts to chemistry to escape from its stout-walled and valveless cocoon (Kafatos & Williams, 1964). A few days prior to emergence the moth secretes a crystalline enzyme, cocoonase, on to the surface of its maxillary galeae. Then, during the process of eclosion, buffer produced in the labial glands is also secreted on to the galeal surface. The resulting protease solution then digests the sericin ‘glue’ from around the silk fibres and thus provides an opening for the moth. After struggling free, the moth clings to the outside of the cocoon and spreads its wings.
Intracellular Studies On Pacemaker and Follower Neurones in the Cardiac Ganglion of Limulus
Authors: Lang Fred
Published: April 2021

Intracellular studies on the cardiac ganglion cells of invertebrates have been confined mainly to the hearts of decapod and stomatopod crustaceans. The cardiac ganglia of these animals contain relatively few neurones, thought to be divisible into large follower cells and small pacemaker cells (for reviews see Hagiwara, 1961 ; Bullock & Horridge, 1965).

Studies on follower cells of crustacean cardiac ganglia are numerous but intracellular studies on pacemaker cells, with one exception (Bullock & Terzuolo, 1957) seem to be limited to the cardiac ganglion of the stomatopod, Squilla (Watanabe et al. 1967a; Watanabe, Obara & Akiyama, 1967b, 1968, 1969). In Squilla the most anterior-cells exhibit pacemaker potentials and fire in bursts with each heart beat. However, all neurones in the ganglion are electrically coupled (Irisawa & Hama, 1965; Watanabe et al. 1967a), and pacemaker activity may also be initiated in the posterior part of the ganglion (Irisawa & Irisawa, 1957; Shibuya, 1961; Brown, 1964). The one study on. pacemaker activity in a decapod heart was made on the two largest of the posterior cells of a crab heart (Bullock & Terzuolo, 1957). These workers found that the neurones fired a burst of overshooting spikes during each heart beat. No pacemaker potentials were present but Bullock & Terzuolo (1957) concluded that these two large cells were spontaneously active since there were no excitatory postsynaptic potentials (EPSP).

The Limulus cardiac ganglion is known to be composed of many hundreds of cells (Patten & Redenbaugh, 1899; Bursey & Pax, 1970). Electrical activity of ganglion cells was studied by Heinbecker (1933, 1936) and Prosser (1943). These workers recorded extracellularly from small pieces of the ganglion in an attempt to isolate single units. Prosser (1943) successfully recorded units firing once per burst and other units firing a train of spikes superimposed on a slow wave during each burst. Intracellular studies have been limited to one investigation of the activity of the largest cells in the ganglion, the large pigmented unipolars. These cells fire a train of attenuated spike potentials’)* superimposed on a slow depolarization, similar to that found in follower cells of crustacean cardiac ganglia (Palese, Becker & Pax, 1970).

In their exhaustive morphological study of the ganglion Bursey & Pax (1970) reported that there were five types of neurones present: large unipolars, bipolars and multipolars and small bipolars and multipolars. Only the large unipolars have been studied electrophysiologically and these have been shown to be follower cells (Palese et al. 1970). A study of the remaining morphological types of neurones has therefore been undertaken in an attempt to assess their role in ganglionic activity.
Bend Propagation by A Sliding Filament Model for Flagella
Authors: Brokaw C. J.
Published: April 2021

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. 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. 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. 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.
Regulation of Water and Some Ions in Gammarids (Amphipoda)
Authors: Sutcliffe D. W.
Published: April 2021

Previous work on Gammarus duebeni from brackish and fresh waters established that a correlation exists between certain features of sodium regulation and the sodium concentration of the particular habitat occupied by a population. In populations from fresh water sodium losses in the urine are reduced and the transporting system at the body surface has a higher affinity for sodium ions (Sutcliffe, 1971). There is also some evidence to suggest that the sodium concentration in the blood tends to fall more rapidly in animals from brackish-water populations than in animals from freshwater populations when they are exposed to media containing less than 10 mM/1 sodium (Sutcliffe, 1967; Sutcliffe & Shaw, 1968). This investigation provides some further information on the regulation of sodium, chloride and potassium in the blood of animals acclimatized to low external concentrations. Chloride regulation at salinities above 2 % sea water was studied by Beadle & Cragg (1940 a), who also found that when G. duebeni was placed in distilled water the blood chloride concentration fell to a lower level in animals from a brackish-water locality compared with animals from a freshwater locality (Beadle & Cragg, 1940b).
Regulation of Water and Some Ions in Gammarids (Amphipoda)
Authors: Sutcliffe D. W.
Published: April 2021

The water content, and the concentrations of sodium potassium and chloride in the blood and body water were determined in Gammaruspulex acclimatized to external salinities ranging from 0·06 mM/l NaCl up to 50 % sea water. The mean body water content remained constant at 79·0–80·3 % body wet weight. The total body sodium and chloride concentrations were lowered in 0·06 mM/l NaCl and increased markedly at salinities above 10% sea water. The normal ratio of body sodium/chloride was 1·45–1· 70, decreasing to 1·0 at 50% sea water. The total body potassium concentration remained constant at 47·5–55·2 mM/kg body H2O. The rate of potassium loss across the body surface was relatively fast. Potassium balance was maintained at an external potassium concentration of 0·010–0·015 mM/l by starved animals, and at 0*005 by fed animals. The proportion of body water in the blood space was calculated from the concentrations of potassium and chloride in the blood and in the body water. The blood space contained 38–42% body H2O in animals from fresh water. The blood space decreased to 31 % body H2O in animals from 0*06 mM/l NaCl. The sodium space was equivalent to about 70 % body H2O. The mean intracellular concentrations of sodium, potassium and chloride were estimated and the results were compared with previous analyses made on the tissues of G. pulex and other crustaceans. It was concluded that in G. pulex from fresh water the distribution of potassium and chloride ions between the extracellular blood space and the intracellular space approximately conforms to a Donnan equilibrium. 30-40% of the body sodium is apparently located in the intracellular space.
An Electrophysiological Study of Parapodial Innervation Patterns in Aplysia Fasciata
Authors: Hughes George M.
Published: April 2021

Studies have been made of the patterns of parapodial innervation in Aplysia fasciata and A. depilans using electrophysiological methods. Sensory fibres are chiefly found in the main parapodial nerves. The areas innervated by these nerves overlap somewhat and such overlapping extends to the branches of individual parapodial nerves. Responses to mechanical stimulation of the parapodial surface gives rise to varying sizes of spike, the smaller spikes being usually more slowly adapting, the larger being highly phasic. Although the general pattern of innervation is common to all specimens there are wide variations in detail. Electrical stimulation of parapodial nerves produces mechanical contractions which are associated with responses in some of the sensory fibres. Usually the afferent units which are stimulated in this way have sensory fields within overlapping areas supplied by the two branches. Such proprioceptive feedback responses usually declined with repetition.
Neural Activation of the Heart of the Lobster Homarus Americanus
Authors: Anderson Margaret , Cooke I. M.
Published: April 2021

Glass microelectrodes were used to record intracellular activity from the striated muscle fibres of the heart of the lobster Homarus americanus. In spontaneously beating hearts bursts of impulses are generated at regular intervals by neurones in the cardiac ganglion. These bursts produce depolarizations of the muscle fibres. Each depolarization is associated with a contraction of the heart. The depolarizations consist of many depolarizing steps; each step is related in a one- to-one manner to a nerve impulse and is believed to be an excitatory junction potential (EJP). The depolarizations (400–700 ms duration in different preparations) exhibit a fast rise to a peak (35-40 mV) followed by a plateau (20–25 mV) which decays to the resting level (51·5 ± 3·2 mV, n = 148). Current-voltage curves indicate that the EJPs do not give rise to regenerative membrane responses. Small, spontaneously produced potentials were recorded in the presence of TTX. Autocovariance tests show that the potentials occur independently and are likely to be miniature junction potentials. Polyneuronal innervation of the muscle fibres was demonstrated by applying stimuli of gradually increasing intensity to the distal ends of cut nerves while recording the responses of a muscle fibre. When a train of stimuli is applied at an intensity to evoke activity from a single axon, the first response of a muscle fibre is usually greater than the second; facilitation of the second and subsequent responses takes place. The degree of facilitation developed depends on the frequency of stimulation. Facilitation decays exponentially with a time constant of a few seconds. In two-pulse experiments the second response was depressed when the interpulse intervals were ⩽ 0·5s. Examples of combined facilitation and depression are presented.
The Effect of Hypoxia and Anaemia on the Swimming Performance of Rainbow Trout (Salmo Gairdneri)
Authors: Jones David R.
Published: April 2021

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). At temperatures close to their acclimation temperatures there was no significant difference between the maximum swimming speeds of the two groups of trout. .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. 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). 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.
Central Control of Auditory Input in the Goldfish: I. Effect of Shocks to the Midbrain
Authors: Piddington R. W.
Published: April 2021

Shocks applied to three midbrain regions reversibly suppressed the click-evoked action potential at the medulla. Clicks in air did not activate lateral-line fibres. Only one midbrain region, the torus semicircularis, showed a distinct afferent auditory response; the other two regions (anterior optic tectum and midbrain below) were used to avoid unwanted antidromic activation of medullary afferents by shocks to the torus. Muscular action on the mechanical auditory pathway was excluded by showing that shocks had no effect on the saccular microphonie or receptor potential. The results are consistent with the action of a descending inhibitory pathway that suppresses auditory input either at the medulla or at the sacculus. One brief shock is effective, but the system is mainly dependent on temporal and spatial summation. The dependency on click intensity may be complex, both high-threshold and low-threshold fibres can be inhibited and occasionally a component of the compound spike shows facilitation instead. Shocks affect the two-click recovery cycle in a complex maimer. Recovery is enhanced if the clicks are presented less than 40 msec after the shocks but depressed at longer intervals, even beyond 500 msec.
Central Control of Auditory Input in the Goldfish: II. Evidence of Action in the Free-Swimming Animal
Authors: Piddington R. W.
Published: April 2021

In the free-swimming electrode-implanted goldfish, the neural response in the medulla to a constant auditory stimulus may exhibit reversible fluctuations in amplitude which are abolished by anaesthesia. The results are consistent with the action of an auditory control system which can reduce or enhance the input following a click. Noise-masking effects and reflex muscular control were excluded by demonstrating the relative constancy of the rectified microphonic during simultaneous changes in the click-evoked action potential at the medulla. There are three kinds of response modification: habituation, rapid inhibitory feedback, and facilitation. Both feedback and habituation act predominantly on high-threshold auditory fibres. Low-threshold fibres do not become habituated, and dishabituation does not occur. As in the mammal, anaesthetic reduces the tendency of the system to become habituated by an amount which depends on the dosage. Auditory fibres with highest threshold have the greatest tendency to become habituated and are the least affected in this respect by anaesthetic. Simple conditioning experiments indicate that control influences exerted over the input can be biased by positive or negative reinforcement which follows the auditory stimulus. The control system may work in attention, in frequency analysis, or in suppressing input to self-made sounds. A new hypothesis is made on the biological significance of hearing in fish. A fish may be able to tell if other swimming fish are approaching, receding, or moving tangentially by analysing the proportions in time of the compressions and rarefactions present in the swimming sounds, which are proposed to be asymmetrical.
Studies on the Adaptation of the Toad Bufo Viridis to High Salinities: Oxygen Consumption, Plasma Concentration and Water Content of the Tissues*
Authors: Katz Uri
Published: April 2021

The toad Bufo viridis was adapted to various salinities up to 800 mOsm NaCl solutions. The blood was always hypertonic to the external solutions and had a high urea concentration. Urea concentration in the plasma was higher in summer than in winter. Urine was hypotonic to the plasma in low salinities and became isotonic with the plasma at 400 mOsm and higher salinities. Water content of the whole body and the skeletal muscles decreased somewhat with salinity. Oxygen consumption was unaffected by salinity when animals were gradually adapted to high salinities. It increased, however, upon acute dehydration whether this was caused by immediate transfer to high salinity or by rapid evaporative dehydration in air.
Neurohormonal alteration of integrative properties of the cardiac ganglion of the lobster Homarus americanus
Authors: Cooke I. M. , Hartline D. K.
Published: April 2021

The spontaneous burst discharges of isolated lobster (Homarus americanus) cardiac ganglia were recorded with a spaced array of electrodes. Small regions (< 1 mm) of the ganglion were exposed to the cardioexcitor neurohormone in extracts of pericardial organs (XPO) or to 10−5M 5-hydroxytryptamine (5HT). All axons were excited (increased mean firing frequency,) by both substances, but only by applications in the region between the soma (but excluding it) and proximal site of impulse initiation. Units not so exposed changed their relatively little despite increases of as much as threefold in exposed units and changes in burst rate and overall length. Regularity and grouping of all impulse activity into bursts was never disturbed. 5HT increases burst rate at any point of application. The increases are larger if small cells are affected than if only large cells are exposed. Burst length decreases except when the pacemaker is affected. In contrast, XPO affects neither burst rate or length unless small cells are affected. Length is increased if nonpacemaker small cells are affected; both rate and length increase if the pacemaker is affected. The pacemaker usually exhibits an of intermediate value. Rate changes are not simply related to its . A small cell can ‘burst’ in the absence of impulses from any other cells. XPO may enhance endogenous ‘driver potentials,’ while 5HT may excite by depolarizing at limited sites.
Properties of A Symmetric Pair of Serotonin-Containing Neurones in the Cerebral Ganglia of Planorbis
Authors: Berry M. S. , Pentreath V. W.
Published: April 2021

There is a bilaterally symmetric pair of large serotonin-containing neurones in the cerebral ganglia of Planorbis corneus. In some animals these neurones are connected by a non-rectifying electrotonic synapse, and fire in synchrony even at prolonged high frequency. In other animals the neurones are not coupled, and fire independently except when driven by common input. Occasionally the coupling is weak. Both coupled and non-coupled serotonin neurones have processes in the major nerve trunks of both buccal ganglia. Synapses are made with many neurones in the buccal ganglia. The serotonin neurones can initiate firing in several motoneurones and thus produce movements of the buccal mass. During spontaneous feeding cycles the input and firing pattern of the serotonin neurones do not bear any obvious relation to the movements of the buccal mass. The data suggest that the serotonin neurones are modulatory cells, altering the level of excitability of buccal ganglion neurones.
An Electrophysiological Study of Mechanisms Controlling Polyp Retraction in Colonies of the Scleractinian Coral Goniopora Lobata
Authors: Anderson Peter A. V.
Published: April 2021

Electrical or mechanical stimulation of Goniopora lobata produces coordinated retraction of polyps in the colony. With repetitive stimulation, the response spreads in linear, radial increments which become successively smaller with each stimulus. Electrical activity recorded from these colonies is interpreted as originating in a conduction system responsible for effecting the colonial retraction response. The electrical activity spreads incrementally through the colony in a similar manner to the behavioural response. Various hypotheses have been proposed to account for such a spread of electrical activity. Of these, only interneural facilitation is of appreciable importance to Goniopora. Temporary termination of a pathway, by the passage of an impulse through it, was found and interpreted as being an additional and important property of the colonial conduction system.
Mechanical Stimulation of Starfish Sperm Flagella
Authors: Okuno Makoto , Hiramoto Yukio
Published: April 2021

The responses of starfish sperm flagella to mechanical stimulation with a microneedle were analysed. Flagellar movement was recorded by high-speed microcinematography and by stroboscopic observation. The amplitude of the bending wave of a flagellum was restricted over its entire length when the microneedle was brought near to the flagellum at its proximal region. Beyond the restricted part, the amplitude of the wave, and the bend angle, became smaller than those of a normally beating flagellum, while the curvature was practically unchanged. When the tip of the microneedle was in contact with the flagellum, propagation of the bending wave beyond the microneedle was inhibited. The part of the flagellum between the base and the microneedle continued beating in some cases and stopped beating in other cases. The flagellum beyond the arrested part stopped beating and remained straight. When the microneedle was removed, the bending wave which existed in the part of the flagellum proximal to the microneedle, or the wave which was passively formed de novo at the time of the removal of the microneedle, propagated over the arrested part towards the tip. A flagellum amputated by a microneedle in a medium containing ATP continued beating with a small amplitude, small curvature, small bend angle and low frequency. When the amputated flagellum was passively bent by a microneedle at the region near the point of amputation, this bend propagated towards the tip with a constant bend angle. The beating frequency of the flagellum could be modulated by the application of a rhythmic external force generated by vibrating a microneedle near the flagellum. The beating was completely synchronized with vibration of the microneedle in the frequency range from 23 Hz to 43 Hz.
Temperature Regulation and Heat Dissipation During Flight in Birds
Authors: Torre-Bueno Jose R.
Published: April 2021

Core and skin temperature were measured by radiotelemetry in starlings (Sturnus vulgaris) during 30 min flights in a wind tunnel. Core temperature was independent of ambient temperature from o to 28 °C. The temporal mean of the monitored core temperature during flight was 42·7 °C in one bird and 44·0 °C in another. These temperatures are 2–4 °C higher than the resting temperature in starlings, and are among the highest steady-state temperatures observed in any animal. Skin temperature on the breast was within a few degrees of core temperature. In some locations skin temperature was higher at low ambient temperatures than at intermediate ambient temperatures. An analysis of the data shows that a high core temperature does not function as an aid to heat dissipation. On the contrary, insulation is adjusted to maintain a high temperature, presumably because it is necessary for flight. The increase in skin temperature at low ambient temperatures is believed to be a result of a decrease in heat flow through the breast feathers brought about by feather adjustments, to compensate for an unavoidable increase in heat flow in unfeathered or poorly feathered parts of the body.
The Physical Properties of Spider’s Silk and Their Role in the Design of Orb-Webs
Authors: Denny Mark
Published: April 2021

Determinations were made of several physical properties of the viscid and frame silks of the orb-webs built by the spider Araneus sericatus (Cl.). Both types of silk show a breaking stress of approximately 1 GN/m2 and an initial resilience of approximately 0·35. The breaking extension ratio of viscid silk (λ = 3·00) is much greater than that of frame silk (λ = 1·25), and the viscid silk relaxes to a relatively greater extent. These properties are correlated with the degree of crystallization of the protein from which the silk is made, this factor being controlled by the sequence of amino acids in the protein. The physical properties of the viscid and frame silks allow them to function effectively as shock absorbers and structural elements, respectively; and allow the orb-web to function as an aerial filter with a minimum expenditure of material and energy.
Solute Secretion by the Tube Foot Epithelium in the Starfish Asterias Forbesi
Authors: Prusch Robert D.
Published: April 2021

The K+ and Cl− levels and osmotic concentration of the tube feet fluid in intact starfish (Asterias forbesi) are higher than that in the external sea water or perivisceral (coelomic) fluid. The increase in K+ in the fluid in the tube feet lumen is brought about by the active secretion of K+ by the tube feet epithelium. No exchange of material from the external environment with the more distal portions of the water vascular system across the madreporite was observed in this study. It is suggested that the fluid volume in the tube feet is maintained by active K+ secretion, by the tube feet epithelium, which creates an osmotic driving force for water into the lumen of the tube feet.
The Effect of Prolonged Exercise on the Lateral Musculature of the Brown Trout (Salmo Trutta)
Authors: Davison William , Goldspink Geoffrey
Published: April 2021

Hatchery-reared brown trout (Salmo trutta L.) were exercised continuously for periods of several weeks at swimming speeds of 1·5, 3·0 and 4·5 body lengths/s and their rates of growth were determined. Changes in the major muscle constituents were determined by biochemical analysis and changes in muscle cells using histochemistry and electron microscopy.

At the lowest speed the fish grew much more rapidly, and converted food into fish flesh much more efficiently than their controls kept in still water. Large stores of glycogen and lipid were built up. Gross changes were observed mainly in red muscle cells, with enlargement of the mitochondria being very noticeable.

The fish swimming at intermediate speed showed greater growth than the controls, although the energy expended in swimming against the water current led to an inefficient food conversion rate. Large stores of glycogen were built up, but lipid levels fell, suggesting that this was the major fuel for swimming at this speed. Changes in all the muscle fibre types were observed.

The energy required to maintain the fish in the water flow at the highest speed was so great as to have serious detrimental effects on the fish, and many did not survive. Those which did survive showed signs of gross depletion.
The Significance of Ground Effect to the Aerodynamic Cost of Flight and Energetics of the Black Skimmer (Rhyncops Nigra)
Authors: Withers Philip C. , Timko Patricia L.
Published: April 2021

The kinematics and aerodynamics of flapping and gliding flight by the black skimmer were investigated to evaluate the significance of ground effect to the foraging and daily energy budget of skimmers. Ground effect is an increase in lift and decrease in drag of an aerofoil when close to the ground.

The duration of upstroke and downstroke, the wing movements and the pronation/supination of the wings during flapping flight of the skimmer are similar to other birds. Wing-beat frequency was 3·1 s−1 and flight velocity was 9·1 m s−1. The wing stroke was markedly asymmetric, with the majority of the stroke occurring above the plane of the body. During skimming, wing beats are intermittent and of low amplitude; flight velocity is 10·3 m s−1.

Induced power, parasite power and profile power of skimmers were calculated after Tucker (1973) in the absence of ground effect, and the glide angle and sink velocity were calculated for gliding skimmers. Ground effect was shown to markedly reduce induced power requirements, and hence total power requirement, of flapping flight, and reduce the glide angle and sink velocity during gliding.

The hydrodynamic drag of the lower mandible was estimated to be 10−4 N, which is insignificant compared to the total aerodynamic drag (0·4 N).

Ground effect was shown to markedly increase foraging efficiency and facilitate the attainment of a positive daily energy balance. The significance of ground effect to other flying vertebrates was discussed.
Circadian Rhythm of Output from Neurones in the Eye of Aplysia
Authors: Benson Jack A. , Jacklet Jon W.
Published: April 2021

The compound action potential (CAP) output from the isolated eye of Aplysia, in darkness at constant temperature, exhibits a circadian rhythm of CAP frequency and a circadian rhythm of CAP amplitude when recorded in culture medium for up to two weeks. Deuterated culture medium lengthened the period of the CAP frequency rhythm linearly from 26-7 h in normal culture medium to 33·7 h in 50% D2O culture medium. In 60 % D2O culture medium, the rhythm of CAP frequency was abolished after a single cycle. Lowering temperature had a direct inhibitory effect on the CAP generating mechanism, so that CAP production was virtually abolished below 7 °C. Lowering temperature decreased the amplitude and increased the period of the rhythm, and in eyes maintained at 9·5 °C the rhythm damped out after several cycles. Between 15 and 22·5 °C there was almost complete temperature compensation (Q10 1·07). It is suggested that the CAP generating cells of the eye may be similar in mechanism to central endogenous bursters in Aplysia and other gastropods, and that the circadian rhythm of CAP frequency and CAP burst frequency may be due to a clock-controlled change in frequency of a membrane potential oscillation in the electrotonically coupled secondary neurones.
Circadian Rhythm of Output From Neurones in the Eye of Aplysia
Authors: Benson Jack A. , Jacklet Jon W.
Published: April 2021

The circadian clock that controls CAP frequency was stopped at or near its lowest phase point by long duration cold pulses of 6 °C. On return to normal recording temperature (15 °C), the rhythm was always reinitiated from this phase point. Following long cold pulses, there was often a transient peak of CAP activity lasting 2–6 h. It is thought that this was an effect of rise in temperature after prolonged cooling and not an effect on the clock itself. Twelve h cold pulses, spanning the rhythm peak, caused phase delays. 9 °C pulses caused small delays (e.g. 1·7 h) while large phase delays (e.g. 6·7 h) followed pulses of 5 °C. Some pulses at an intermediate temperature (8·5 °C) caused abnormal post-pulse cycles lasting several days, and resulting in very large phase delays (10-14 h). The abnormal CAP frequency curves following 12 h cold pulses of 8·5 °C spanning the rhythm peak are interpreted as rhythm splits. It is postulated that part of the population of coupled oscillators comprising the circadian clock was slightly delayed by the cold pulse, while the other part was driven further towards the ‘stopped’ state, thus producing a large phase angle difference between the two subpopulations. These drew one another back into phase during several cycles to reform a normal circadian rhythm. It is hypothesized that the circadian oscillations of the two subpopulations did not sum to produce the observed CAP frequency curve; rather the level of CAP output was controlled by whichever subpopulation was discharging at the higher frequency.
Further Evidence for Na/NH4 Exchange in Marine Teleost Fish
Authors: Evans David H.
Published: April 2021

Four species of marine teleosts were shown to possess an external-NH4- inhibited Na uptake from 1 mM-NaCl solutions. The inhibition was not due to changes in the transepithelial potential. Injection of 2 μM-NH4/g fish stimulated Na uptake by Opsanus beta and also stimulated ammonia efflux, 50% of which was dependent upon external Na. The ammonia efflux from three species was partially dependent upon external Na. Na/NH4 exchange in O. beta could be reversed so that 22Na efflux could be stimulated by the addition of 200 mM-NH4 to the external solution. These studies show clearly that marine teleosts possess an Na/NH4 exchange system in sea water which results in a net influx of Na into the fish.
Control of Cuticle Extensibility in the Wings of Adult Manduca at the Time of Eclosion: Effects of Eclosion Hormone And Bursicon
Authors: Reynolds Stuart E.
Published: April 2021

The wings of pharate adult tobacco hornworm moths, Manduca sexta, are relatively inextensible until 3 or 4 h before emergence from the pupal case. At this time the wing cuticle becomes plasticized, so that by the time of eclosion, the wings are readily extensible. This change in the mechanical properties of the wing cuticle is shown to be under the control of a factor from the head. This factor is present in the corpora cardiaca/corpora allata complex, and in the protocerebrum of the brain, being released into the blood prior to eclosion. It is able to act directly on isolated wings. The active principle was found to be indistinguishable in a number of ways from the hormone which triggers emergence from the pupal case, the eclosion hormone. Partial purification of the eclosion hormone failed to separate activity causing eclosion from activity causing wing cuticle plasticization. It is concluded that the same hormone is probably responsible for both effects. The cuticle plasticizing activity of the eclosion hormone forms the basis for a new, highly sensitive bioassay.

Another factor, distinct from the eclosion hormone, is able to cause wing cuticle plasticization. This factor is found in the abdominal nerve cord, and is only released into the blood after eclosion has occurred. It is probably identical with the tanning hormone, bursicon, which is released at this time. The factor in the nerve cord which causes cuticle plasticization is indistinguishable from bursicon in a number of ways, including partial purification by gel filtration. Bursicon evidently causes a further increase in wing cuticle extensibility after eclosion, at the time of wing inflation.
Evidence That Octopus is Colour Blind
Authors: Messenger J. B.
Published: April 2021

Six octopuses were trained on a series of visual discrimination tasks where the discriminanda were presented simultaneously, and where different tasks alternated in a single training session. All the octopuses could make discriminations based on brightness and orientation over the same period of time. Over a period in which all octopuses discriminated a black from a white vertical rectangle none discriminated a yellow vertical rectangle from a grey (of matching brightness). Over a period in which all octopuses discriminated a vertical from a horizontal grey rectangle none discriminated a violet vertical rectangle from a matching grey. The behaviour of the octopuses was qualitatively different in the hue versus grey situations, their attacks being considerably slower and less certain. These results, which agree with previous behavioural findings and a variety of morphological, physiological and biochemical evidence, make it increasingly probable that Octopus vulgaris is colour blind.
The Role of the Cardiac Vagus in the Response of the Dogfish Scyliorhinus Canicula to Hypoxia
Authors: Taylor E. W. , Short S. , Butler P. J.
Published: April 2021

During normoxia, heart rate was governed by a vagal tone which increased at higher acclimation temperatures. This tonic influence was exerted predominantly via the branchial cardiac nerves. The increase in heart rate following atropinization or cardiac vagotomy was associated with a reduction in stroke flow in the ventral aorta in accordance with Starling’s Law of the heart. During slowly induced hypoxia there was a reflex bradycardia, the onset and extent of which varied with acclimation temperature, and which was mediated predominantly via the pair of branchial cardiac vagi. The branchial cardiac vagi were also wholely responsible for the transient marked bradycardia at the onset of rapidly induced hypoxia. Direct measurement of blood flow to the anterior two pairs of branchial arteries demonstrated that they received approximately 37 % of total cardiac output in normoxia and that this proportion was unchanged during hypoxia. The bradycardia during hypoxia in control animals was partially offset by a rise in cardiac stroke volume so that cardiac output decreased slightly. Injection of the adrenergic βreceptor blocker, Propranolol, abolished the increase in stroke flow during hypoxia, but did not effect the bradycardia, and the total blood flow was therefore reduced. The values of during hypoxia from fish acclimated to 17 °C were significantly reduced from the control values following atropinization and either branchial cardiac vagotomy or total cardiac vagotomy. The apparent power output of the heart was reduced during hypoxia at high acclimation temperatures due to the marked bradycardia.
The Relative Importance of Nervous, Humoral and Intrinsic Mechanisms in the Regulation of Heart Rate and Stroke Volume in the DogfishScyliorhinus Canicula
Authors: Short S. , Butler P. J. , Taylor E. W.
Published: April 2021

Experiments involving supra-maximal electrical stimulation of the vagus have indicated that the stimulation of the peripheral cut ends of the branchial cardiac branches produces a more intense cardio-inhibition than the stimulation of visceral cardiac branches. It is suggested that the visceral cardiac branches may have a mainly sensory function. In no case could cardioacceleration be obtained during vagal stimulation either before or after injection of atropine, and any increases in stroke volume that occurred accompanied reductions in heart rate. This relationship was considered to be a manifestation of Starling’s Law of the heart and it has been concluded that there is no augmentary sympathetic innervation to the dogfish heart. Evidence also indicates that the Starling relationship is responsible for the increase in stroke volume which accompanies the bradycardia during hypoxia. Circulating catecholamines do not appear to be of importance in this response although they are concerned in cardio-vascular regulation during normoxia.
The Nervous Control of Limb Autotomy in the Hermit Crab Pagurus Bernhardus (L.) and the Role of the Cuticular Stress Detector, CSD1
Authors: Findlay Ian , McVean Alistair
Published: April 2021

Limb autotomy results from the fracture of a preformed breakage plane within the second limb segment. Fracture is produced by the contraction of the large anterior levator (AL) muscle at the same time as its synergist, the posterior levator (PL) muscle. The AL force is thus directed on to a small portion of the breakage plane; withdrawal of this plug initiates cuticular fracture. Autotomy is a response to damage inflicted on the limb. In the absence of sensory information from the second limb segment there is less activity in the units serving the PL. It is shown that stimulation of the sense organ, cuticular stress detector one, provides feedback to PL motor neurones. The feedback is an integral part of the nervous control of limb autotomy.
Estimation of Shunting, Systemic and Pulmonary Output of the Heart, and Regional Blood Flow Distribution in Unanaesthetized Lizards (Varanus Exanthematicus) by Injection of Radioactively Labelled Microspheres
Authors: Berger P. J. , Heisler N.
Published: April 2021

Circulatory parameters in a lizard (Varanus exanthematicus) were determined using the microsphere method. Microspheres (MS) (slightly larger than the erythrocytes and labelled with different γ-emitting isotopes) were injected into a pulmonary vein or the left atrium for determination of the left-to-right (L-R) shunt and the regional distribution of the ventricular systemic output. Injections were also made into the sinus venosus for determination of the right-to-left (R-L) shunt. The relative blood flow was obtained as the ratio of the MS activity found in the various tissues over the total activity injected. Absolute calibration of the method was performed by introduction of an ‘artificial organ’into the circulatory system (Hales, 1973).

Ventricular systemic output (VSO), in five animals, averaged 121 ml/ (min.kg) and ventricular pulmonary output 119 ml/(min.kg). The value of VSO was significantly higher than those observed in other lizard species. In all experimental animals both R-L as well as L-R shunting of various extent occurred. The reliability of the microsphere method as applied in lizards is discussed and is considered to be relatively accurate even under conditions of incomplete mixing of shunted and unshunted blood in systemic heart output.
The Influence of Diet, Age and State of Hydration on Na+, K+ and Urate Balance in the Fat Body of the Cockroach Periplaneta Americana
Authors: Tucker Lois E.
Published: April 2021

The effect of diet, age, sex and state of hydration on the relationship between Na+, K+ and urate in the fat body tissue of the cockroach Periplaneta americana has been investigated. There is a significant correlation between K+ and urate concentrations in the fat bodies of both males and females in late nymphal and adult stages. Animals fed on a dextrin/casein diet, which had a K+ content of about one-third that of the rat pellets normally used for food, had a lower than normal K+/urate ratio. In both the normally fed and dextrin/casein-fed groups of animals, dehydration caused a decrease in the K+/urate ratio. Dehydration (and starvation) caused an increase in the amount of urate per unit weight of fat body. Some of the urate in the fat body is present in small spherical cellular inclusions. There is also a correlation between the K+ concentration and the number of spherules. The ratio of spherules/urate is significantly higher in hydrated animals than in dehydrated ones.
Respiratory and Cardiovascular Responses of the Pigeon to Sustained, Level Flight in A Wind-Tunnel
Authors: Butler P. j. , West N. H. , Jones D. R.
Published: April 2021

Five pigeons were trained to fly in a boundary-layer wind-tunnel at a velocity of 10 m s−1 for at least 10 min, and a number of respiratory and cardiovascular variables were recorded. For comparison, heart rate, respiratory frequency and E.M.G. from the pectoralis major muscles were also recorded, using radio-telemetry, from free-flying pigeons. For the flights in the wind tunnel there were immediate increases in respiratory frequency and heart rate upon take-off; these variables continued to increase during the flight, eventually becoming on average 411 breaths min−1 (20 × resting) and 670 beats min-1 (6 × resting) respectively. There was a 1:1 relationship between ventilation and wing beat. Oxygen uptake and carbon dioxide production reached their highest values of 12·5 × and 14·4 × resting respectively within 1 min of take-off and then declined to steady levels of 200 ml kg−1 min S.T.P.D. (1O × resting) and 184 ml kg−1 min S.T.P.D. (10·7 × resting) 4 min after take-off. If allowances are made for the weight and drag of the mask and tubes, these stable values are at least 12 % higher than would occur in an unloaded bird. Body temperature rose steadily after take-off, reaching a stable value of 43·3 °C, which was 2 °C above resting, after 6 min of flight. There was a 1·8 × rise in content difference and little change in cardiac stroke volume during night, so that the rise in heart rate was the major factor in transporting the extra O2 to the active muscles. Respiratory quotient rose from 0·85 at rest to 0·99, 30 s after take off, and then fell to 0·92 after 7 min of flight. Blood lactate rose to 59·8 mg% (6·5 × its resting value). Comparisons with the free-flying birds indicated that the pattern of flight in the wind tunnel was somewhat abnormal, especially at the beginning of a flight, and this may account for the value of being higher at the start of a flight and then declining to a steady value as the flight progressed. Upon landing, heart rate, and body temperature began to fall immediately, and within 2 min, heart rate, and had returned to the ‘tunnel on’ resting values. Respiratory frequency increased upon landing and its decline closely matched the fall in body temperature. R.Q. rose above unity immediately upon landing as CO2 was removed in excess of its metabolic production, and then fell below the resting value as CO2 was retained, presumably to maintain acid/base balance during the metabolism of lactic acid.
The Influence of Age, Diet and Lipid Content on Survival, Water Balance and Na+ and K+ Regulation in Dehydrating Cockroaches
Authors: Tucker Lois E.
Published: April 2021

In dehydrating conditions late instar nymphs lose weight more slowly and survive longer than adult Periplaneta americana. This appears to be due, at least in part, to the larger lipid stores which are found in the fat bodies of the nymphs. When the water loss from an animal is greater than the amount of metabolic water obtained from the catabolism of stored foods, water is removed from the haemolymph in order to maintain water balance in the tissues. Dehydration for 6 days causes the haemolymph volume to decrease markedly in most adults, but the haemolymph Na+ and K+ concentrations increase only slightly. During dehydration the mean Na+/K+ ratio of the fat body tissue increased in adults, except in those which had been fed on pure carbohydrate prior to dehydration. Although not always statistically significant on account of the large variances, the changes in mean Na+, K+ and in the Na+/K+ ratio suggest there is an increase in Na+ and decrease in K+ in the fat body of animals where the haemolymph volume is markedly reduced by dehydration.
Regulation of Ions in the Haemolymph of the Cockroach Periplaneta Americana During Dehydration and Rehydration
Authors: Tucker Lois E.
Published: April 2021

Experiments using 22Na-uptake and serial sampling techniques showed that during dehydration Na was taken up by the fat body in adult Periplaneta americana, but not in nymphs. Generally, accumulation of Na in the fat body was highest in animals which had little reserve lipid and in those which excreted the smallest amounts of Na during the dehydration period.

Dehydration caused little change in the Cl− concentration in the haemolymph. From results of 36Cl-uptake experiments, it appears that the fat body is not involved in the regulation of haemolymph Cl− during dehydration. In old adults, the hindgut was the tissue in which dehydration caused the greatest increase in 36C1 uptake.

The mechanisms which enable cockroaches to withstand dehydrating conditions are discussed.