bluuebunny/crossref_metadata_2025 huggingface dataset:
The Distribution and Exchange of Some Ions and Molecules in the Central Nervous System ofPeriplaneta AmericanaL.
Authors: Treherne J. E.
Published: April 2021

The rapidly exchanging 24Na fraction was found to account for approximately a third of the sodium contained in desheathed terminal abdominal ganglia which had been previously made radioactive by the injection of labelled ions into the haemolymph. This rapidly exchanging sodium was associated with the extracellular spaces which, with the aid of 14C-inulin, were shown to contain 18·2 % of the ganglion water. Using this figure it was possible to calculate that the extracellular sodium concentration exceeded that in the haemolymph by a factor of 1·8 and was 2·5 times greater than that in the cellular fraction of the ganglion. Experiments using 22Na, 42K, 45Ca, 36Cl and 3H0H showed that the concentrations of the ions in the rapidly exchanging extracellular fractions of isolated abdominal nerve cords were different from those of the external medium. The three cations were maintained at considerably higher concentrations in the extracellular spaces, chloride ions being present at a much lower concentration than in the external solution. It was concluded that the ions were distributed between the extracellular spaces and the external solution according to a Donnan equilibrium. The evidence would seem to indicate that a significant proportion of the free anion groups in the extracellular spaces may be those of protein molecules in solution. An appreciable portion of the cations may also, however, be associated with the free anion groups of structural elements such as collagen and mucopolysaccharides. It is suggested that the relatively rapid depolarization observed in desheathed preparations, as compared with intact nerves, in conditions of high external potassium concentration may result from the effects of the disruption of the Donnan equilibrium as well as to any properties of the nerve sheath as a diffusion barrier. It was shown that because of their positive charges the diffusion of the cations in the extracellular spaces occurred more slowly than would be expected on the basis of their free-diffusion constants. The efflux of 14C-inulin also occurred more slowly than would be expected from its free diffusion, an effect probably caused by the passage of the polysaccharide molecules through relatively small spaces in the extracellular system.
Pharyngeal Proprioceptors in the Dogfish Squalus Acanthias L.
Authors: Satchell G. H. , Way H. K.
Published: April 2021

Hughes (1960) described the respiratory cycle of Scyliorhinus as commencing with a contraction of the oro-and para-branchial cavities; this phase occupies about one quarter of a cycle and is succeeded by an expansion of these cavities which is rapid at first and terminates in a pause before the next respiration. A similar series of events occurs in the dogfish Squalus acanthias L.
Osmotic Regulation in the Green Toad (Bufo Viridis)
Authors: Gordon Malcolm S.
Published: April 2021

The osmotic and ionic regulatory abilities of adults of a freshwater population of the green toad (Bufo viridis) have been studied. These toads tolerated environmental salinities as high as 19%,, at temperatures near 25°C. Two individuals of another population of this species tolerated salinities as high as 23 ‰. Changes in body weight of toads transferred to different environmental salinities indicate that the skin of this form is permeable to water. Rapid return to control levels of body weight indicate that drinking of external medium may be an important part of the initial adjustment to high salinities. Above salinities of about 8%0 plasma Δ rises with increasing environmental Δ. Marked hypertonicity of the plasma is maintained in low salinities, but isotonicity with the medium is approached in higher salinities. Increases in plasma concentration above freshwater levels are due primarily to increased NaCl concentration (about 84%), partly to increased concentrations of urea (5–10%) and other osmotically active substances. Urinary Δ is much lower than plasma Δ in dilute media, but becomes identical with plasma Δ above salinities of about 15 ‰. Increases in urine concentration above freshwater levels are also due primarily to NaCl increase (74%). Considerable quantities of salt are lost via the urine. The kidneys seem to lose much of their ability to regulate urinary salt concentrations in high-salinity media. Measurements of electrical potential and short-circuit current indicate that active uptake of inorganic ions by the skin continues in concentrated media, but at reduced rates. Changes in muscle water, Na and K contents indicate the occurrence of some redistribution of water and salts between various body-fluid compartments as part of the salinity adaptation process. In preference experiments, B. viridis chooses the land over any aquatic environment. Among aquatic environments it prefers those with salinities below 8‰. When combined with some earlier data by other workers who studied other populations of B. viridis, the present data indicate great uniformity of ionic and osmotic regulatory abilities among populations of this species. The marked differences between salinity tolerances of different populations are indicated to be due to differences in tissue tolerance of high body-fluid salinities.
Force Exerted by a Single Cilium of Mytilus Edulis
Authors: Yoneda Mitsuki
Published: April 2021

A cilium can be stopped by applying the tip of a glass microneedle during the effective stroke. The force required to stop the cilium has been measured by the author by the displacement of a flexible needle on the basis of its compliance. This force was expressed in terms of a torque, at the base of the cilium, which was 4× 10−7 dyne. cm. The second step would be to know the magnitude of the torque when the cilium is beating freely without constraint. Such a study would require a hydrodynamical treatment, as was given in the case of swimming spermatozoa (Taylor, 1951, 1952; Hancock, 1953; Gray & Hancock, 1955; Machin, 1958; Carlson, 1959).
Proprioceptive Control of Posture in the Crayfish Abdomen*
Authors: Fields Howard L.
Published: April 2021

Sense organs responsive to the changes produced by an animal’s own musculature are common in complex, flexible motor systems, and it is probably safe to assume that proprioceptive feedback is required for these systems to operate with precision. The crustacean muscle receptor organ (MRO) first described by Alexandrowicz (1951) has, because of its accessibility, ease of isolation and hardiness, proven particularly amenable to electrophysiological study. However, the study of this receptor has until recently been confined to mechanisms of transduction and to the excitatory and inhibitory control of its output.
The Motion of Euglena Viridis: The Role of Flagella
Authors: Holwill M. E. J.
Published: April 2021

Analysis of high-speed cine-films of Euglena viridis reveal that the organism traverses a complex three-dimensional path while helical waves are propagated from base to tip along the flagellum. Theoretical analysis shows that the rapid forward velocity of the organism cannot be produced by the body movement alone. The propulsive force generated by the flagellum is sufficient to maintain the observed velocities. Although the euglenoid flagellum bears mastigonemes the thrust produced by it is in the direction to be expected if the flagellum were smooth. Possible explanations of this observation are given.
Gradients in the Insect Segment: The Orientation of Hairs in the Milkweed Bug Oncopeltus Fasciatus
Authors: Lawrence Peter A.
Published: April 2021

During metamorphosis in Oncopeltus the hair-forming cells orient to some unseen influence in the epidermis. The hairs can thus be used as indicators of the polarity of this influence. Excision of the intersegmental membrane can cause a total inversion of the direction of hair outgrowth in the nearby region. Individual insects, each with a large gap in the intersegmental membrane and an associated pattern of hairs which are unusually oriented, occur occasionally in the culture. A study of these defects, and of Locke’s observations on the segmental gradient of Rhodnius, leads to the development of a sand model which can be applied not only to the experiments of Locke on the ripple pattern of Rhodnius, but also to those of Piepho on the orientation of scales in Galleria. The sand model helps in a description of the hypothetical chemical basis of the gradient in the insect segment. The relationship between the gradient and pattern is briefly discussed.
Sodium Regulation in the Amphipod Gammarus Duebeni from Brackish-Water and Fresh-Water Localities in Britain
Authors: Sutcliffe D. W.
Published: April 2021

A quantitative study of sodium influx and loss rates was made on Gammarus duebeni obtained from brackish-water localities. Both influx and loss rates were immediately doubled by a rise in temperature from 10 to 20 ° C. It is estimated that when animals are fully acclimatized to a series of media decreasing from 50 to 2 % sea water the rate of sodium uptake at the body surface is doubled to balance the rate of sodium loss, which is also doubled. The increased loss rate is due equally to an increase in the rate of diffusion across the body surface and to loss in hypotonic urine containing about 160 − 190 mM/1. sodium. Diffusion losses normally account for at least 35 % of the total losses, even when the urine is isotonic with the blood. The sodium-transporting system at the body surface is fully saturated at an external concentration of about 10 mM/1. NaCl (2% sea water). The system has a low affinity for sodium ions and is only half-saturated at 1·5 − 2·5 mM/1. sodium. The overall rate of uptake is increased to its maximum rate to balance sodium losses when in fresh water. When acclimatized to fresh water (0·25 mM/1. NaCl) the sodium loss rate is greatly reduced. This was partly due to a lower rate of diffusion across the body surface following a fall in the blood sodium concentration, and mainly due to elaboration of a very dilute urine. It is suggested that increases in sodium uptake in the antennary glands, resulting in a hypotonic urine, are linked with increases in uptake at the body surface. Both uptake systems are possibly activated by a single internal regulator responding to changes in the blood concentration. Sodium regulation at concentrations below 10 mM/1. NaCl was examined in G. duebeni obtained from fresh-water streams on the Lizard peninsula, the Kintyre peninsula, and the Isle of Man. The regulation of sodium uptake and loss is very similar to regulation in brackish-water animals, and the sodium-transporting system has the same low affinity for sodium ions at concentrations below about 10 mM/1. It is suggested that fresh-water localities in north-west Europe, excluding Ireland, have been colonized from brackish water without any modifications in the sodium-regulatory mechanism. But the fresh-water animals tolerate very low sodium concentrations better than brackish-water animals. This is apparently due to natural selection of individuals in which the sodium uptake rate is higher than the average uptake rate in brackish-water animals.
Case Construction, Movement, Spatial Distribution and Substrate Selection in the Larva of Chironomus Riparius Meigen
Authors: Edgar W. D. , Meadows P. S.
Published: April 2021

Larvae of Chironomus riparius construct their cases from algae in a stereotyped manner. Mud and a mixture of mud and algae can be used instead of algae, although not so successfully. Larvae cannot build cases from sand, and when presented with this substrate they alternate periods of active swimming with resting on the substrate. This is reminiscent of the behaviour of marine larvae as they test substrates before settling. Larvae space out on an algal substrate. Nearest-neighbour analysis has been used to quantify spacing out, and has shown that under experimental conditions initially clumped animals become regularly distributed over a period of time. As larvae age, they move more slowly and are also less likely to move. In substrate-choice experiments larvae prefer an algal to a sand/gravel substrate. Substrate selection is less marked in old larvae. This could be due either to a loss of ability to discriminate between substrates with age, or to a reduction in the rate of movement with age.
Burst Activity and Cellular Interaction in the Pacemaker Ganglion of the Lobster Heart
Authors: Connor John A.
Published: April 2021

The patterned burst activity of cardiac pacemaker ganglion cells in Homarus americanus has been studied by means of intracellular recording electrodes. Burst activity, highly similar to that seen in cells of intact ganglia, has been demonstrated in ganglion sections containing as few as two large-cell bodies. Studies of the sectioned preparations have shown that potential deflexions during the burst period are mainly endogenous activity of the respective cells and not post-synaptic potentials. The behaviour of the cells in the period between bursts suggests the action of an inhibitory conductance change in each of the cells during this period.
Water Uptake and Embryonic Development in Eggs of Chorthippus Brunneus Thunberg (Saltatoria: Acrididae)
Authors: Moriarty F.
Published: April 2021

The pattern of water absorption by eggs of Chorthippus brunneus varies greatly between individuals. The time at which water is absorbed does not have a close relationship with the stage of embryonic development. Water absorption is not essential for prediapause development. Eggs can only undergo blastokinesis and further development, after diapause is broken, if some water has been absorbed. The rate of water loss or gain varies with the osmotic pressure of sodium chloride solutions. Eggs which have started to absorb water appear to become desiccated more rapidly than eggs which have not.
Locust Wind Receptors
Authors: Camhi Jeffrey M.
Published: April 2021

The cervical connective of the desert locust contains interneurones giving responses of four different types to wind stimulation of the facial wind receptor setae. The four categories are : (a) ‘Wind-indicator cells’, giving a slowly adapting response to wind from any of a wide range of directions. (b) ‘Wind-direction cells’, displaying fairly slowly adapting responses, and sensitive to wind only within a very narrow range of directions. Pivoting wind into a cell’s optimal direction evokes a full response. (c) ‘Recentre cells’, showing rapidly adapting responses to wind onset from a fairly wide directional range. Rapidly shifting the wind direction from only one preferred side into the centre evokes a vigorous burst. (d) ‘Acceleration cells’, giving a rapidly adapting response which is especially pronounced for rapid wind accelerations. Interneurones connect with several sensory setae, whose spatial distribution and angles of curvature are unique to each interneurone type. A suggested integrative mechanism relates the angles of curvature of the input setae to the direction response of each interneurone type. The responses suggest roles for certain interneurone categories in flight maintenance and yaw-correcting reflexes.
Membrane Properties of the Somatic Muscle (Obliquely Striated Muscle) of the Earthworm
Authors: Hidaka T. , Ito Y. , Kuriyama H.
Published: April 2021

The membrane properties of the longitudinal muscle fibre of the earthworm Pheretima communissima were investigated by intra- and extracellular stimulating methods. The membrane potential was − 35·4 mV., and spontaneous discharges with overshoot (mean +18 mV.) and after-hyperpolarization (− 60 mV.) were recorded. Tetrodotoxin (10−7 g./ml.) blocked nervous activity but did not influence the spontaneous discharges or the spikes elicited in the muscle fibre by intracellular stimulation. The critical membrane potential required to elicit a spike was not constant, and the falling phase of the spikes was markedly dependent on the level of the membrane potential. The chronaxie, measured from the intensity-duration relation to elicit a spike by intracellular stimulation, was 55 msec. When nervous activity was excluded the propagation of excitation in longitudinal muscles was decremental.
Neuromuscular Transmission in the Longitudinal Layer of Somatic Muscle in the Earthworm
Authors: Hidaka T. , Ito Y. , Kuriyama H. , Tashiro N.
Published: April 2021

The properties of the miniature inhibitory junction potentials (M.I.J.P.) and the inhibitory junction potentials (I.J.P.) elicited by nerve stimulation were investigated in longitudinal muscle fibres of the earthworm. Histograms of the amplitudes (mean, 0·71 mV.) and the intervals (mean, 101 msec.) of the M.I.J.P. showed skew curves. The polarity of the M.I.J.P. was reversed at about —60 mV. When the external chloride was substituted by glutamate the M.I.J.P. disappeared as an external chloride concentration of 15-20 mM, and further reduction reversed their polarity. Picrotoxin blocked generation of the M.I.J.P. and the I.J.P. The cross-over point of the current-voltage relation curves, with and without presence of GABA, occurred at a membrane potential of − 54 mV. in potassium-free solution, and at − 56 mV. in potassium-excess solution. Iontophoretic application of GABA produced slow hyperpolarization. The equilibrium potential of the GABA-potential was about − 60 mV. During the time course of the GABA-potentials an increase in the membrane conductance was observed. Miniature excitatory junction potentials (M.E.J.P.) and excitatory junction potentials (E.J.P.) could be recorded from the longitudinal muscle, but the M.E.J.P. were rare. D-tubocurarine, but not atropine, completely blocked the M.E.J.P. and E.J.P. Prostigmine enhanced their amplitude and duration. The reversal potential level for the E.J.P. was about o mV. Sodium-free solution lowered the reversal potential level for the M.EJ.P. to −20 mV.
The Mechanical Properties of the Longitudinal Muscle in the Earthworm
Authors: Hidaka T. , Kuriyama H. , Yamamoto T.
Published: April 2021

A study of the mechanical properties of longitudinal muscle in relation to the membrane properties was carried out under isometric conditions. When the stimulus duration exceeded 50 msec., active tension development was followed by sustained contraction. The sustained contractions were not related to spike generation. The critical potassium concentration to produce the contracture depolarized the membrane from –36 to –20 mV. Reduced sodium concentration and increased calcium and increased potassium (up to 27 mM) concentrations enhanced the amplitude of the active tension. Reduced sodium concentration enhanced the amplitude and duration of the sustained tension, but increased potassium and calcium concentrations reduced them. Caffeine (12 mM) induced contractures of the muscle, and reduced the membrane resistance and capacitance. Spikes were not elicited by intracellular stimulation. 5-Hydroxytryptamine (10−6 g./ml.) blocked the generation of the sustained contraction but no effect was observed on the phasic tension.
Common Inhibitory Motoneurones in Insects
Authors: Pearson K. G. , Bergman S. J.
Published: April 2021

The innervation patterns of the metathoracic posterior coxal levator muscles of the cockroach, Periplaneta americana, have been investigated, and the mechanical effects produced by activity in the axons to these muscles studied. These muscles are innervated by four excitatory and two inhibitory axons. The three smallest excitatory axons may be classified as slow and the largest as fast. Some single muscle fibres are quintuply innervated by all but the fast axon, and some may be innervated by all six. One of the inhibitory axons is a branch of a common inhibitory neurone. This neurone sends branches out all but one of the ipsilateral nerve trunks to innervate synergic and antagonistic muscles. A similar common inhibitory motoneurone has been found in both the locust species, Locusta migratoria and Schistocerca gregaria. In the locust two branches of this common inhibitory neurone correspond to the inhibitory axon innervating the extensor tibiae muscle and the inhibitory-conditioning axon innervating the anterior coxal adductor muscle. Possible functions of common inhibitory neurones in insects are discussed. In the cockroach this neurone may have a dual function: (a) to regulate leg position when the animal is standing, and (b) to facilitate relaxation of the depressor muscles; this allows a more rapid and stronger leg levation when the animal is walking.
Salt and Water Regulation in the Embryos of Freshwater Pulmonate Molluscs
Authors: Beadle L. C.
Published: April 2021

The envelope and capsular membranes which separate the eggs from the external water are freely permeable to water and inorganic ions. The capsular membrane of B. sudanica is permeable to sucrose (M.W. 342) but not to raffinose (M.W. 504), that of L. stagnalis is permeable to raffinose but not to Carbowax (polyethylene glycol, M.W. 3000 – 3300). By means of 22Na it was shown that, as expected, the concentration of sodium in the capsular fluid of B. sudanica is approximately equal to that in the external water. The initial colloid osmotic pressure of the capsular fluid of B. sudanica is equivalent to that of approximately 1·5 mM/1. solution of non-electrolyte and of L. stagnate to that of 4 – 5 mM/1. Observations on embryos of B. sudanica extracted from the capsular fluid and kept in lake water support the contention that, at least from late cleavage stages onwards, they are capable of active salt and water regulation.
Salt and Water Regulation in the Embryos of Freshwater Pulmonate Molluscs
Authors: Beadle L. C. , Beadle S. F.
Published: April 2021

By means of 22Na it is shown that the embryo takes up sodium from the water via the capsular fluid so that its sodium content is increased more than seven times between the blastula and hatching. Experiments with water of low sodium content (Text-fig. 3): (a) suggest that sodium is taken up by the preblastula embryo, and (A) demonstrate that the embryo can develop with a sodium content less than one-seventh of the normal. Embryos at blastula or even cleavage stages, when deprived of access to external water and ions by mounting over paraffin, can still accomplish the greater part of their development, thus confirming the conclusion 2(b). These experiments also suggest other ions than sodium can be considerably reduced without harm to the embryo. There is evidence, however, that the ecologically inhibiting effect of very low salinity water is due to the low level of ions other than sodium. Reduction of dissolved oxygen to o· 1-0· 2 mg./l. for 12 hr. completely inhibits sodium uptake and visible development. These are both reversible but, though the normal rate of development is resumed at once, the rate of sodium uptake is not restored for several days after re-aeration. The ultimate effect of this treatment on some, but not all, embryos is an upset of water balance shown by swelling and the suppression of the final stages of development.
Salt and Water Regulation in the Embryos of Freshwater Pulmonate Molluscs
Authors: Beadle L. C.
Published: April 2021

Subjection of 2-cell stages, later cleavage stages and blastulae of Biomphalaria sudanica to anoxia, 1 MM/1. cyanide and a temperature of about 7° C. causes a great swelling of the cleavage cavity and blastocoel. This effect is reversible if the treatment is not too prolonged. Such temporary treatment at early stages has no apparent permanent effect on many of the embryos, but in some the water-regulating mechanism breaks down again at a later stage (postgastrula). The subject may become enormously distended by swelling of the body cavity, and development is halted. Swelling in both (1) and (2) is apparently confined to the extracellular cavities, the cells remaining intact and not obviously swollen. The older embryos subject to delayed swelling (2) can remain in this condition for many days after control embryos from the same mass have hatched. Experiments with MNa on a delayed swollen embryo suggested that, though water control was seriously impaired, the mechanism for the uptake of sodium into the body cavity was still functioning. The possible significance of these observations in relation to the mechanism for fluid control in the normal embryo is discussed. Many problems remain unsolved and suggestions are made for further work.
Organization of the Giant Axons of the Cockroach Periplaneta Americana
Authors: Spira M. E. , Parnas I. , Bergmann F.
Published: April 2021

Stimulation of the connectives between the suboesophageal and prothoracic ganglia of the American cockroach induced ipsilateral descending spikes in the abdominal giant axons with an average delay of 0·6 msec, per thoracic ganglion. Nicotine at 5 μ g./ml. had no effect on conduction in the abdomen but blocked ascending responses sequentially at the 6th abdominal ganglion then at the levels of T1; T2, and T3. Simultaneous descending and ascending impulses resulted in mutual extinction along the nerve cord with the point of collision depending on the interval between stimuli. It is suggested that a common pathway subserves ascending and descending giant impulses and models for bi-directional conduction are discussed.
Studies on the Permeability To Water Of Selected Marine, Freshwater And Euryhaline Teleosts
Authors: Evans David H.
Published: April 2021

Measurements were made of the flux of tritiated water across various marine, freshwater and euryhaline teleosts. The effects of temperature, body size, species differences, salinity, stress and anaesthetization were studied. The Q10 of the flux of water across teleosts is approximately 1·90 and the flux is related to the o-88 power of the body weight. All of the freshwater species studied were more permeable to water than the marine species. Euryhaline teleosts appear to have about the same permeability as species to which they are most closely related. While the flounder and the yellow eel are more permeable to water in fresh water than in sea water, the silver eel and the brown trout do not change their permeability and the 3-spined stickleback is less permeable to water in fresh water than in sea water. While stress markedly increases the permeability to water of large brown trout, it has no effect on small brown trout and seems to decrease the water permeability of the plaice. Anaesthetization has no effect on the water permeability of the goldfish but markedly increases the permeability to water of the silver eel. The relationship between the flux of water and either the drinking rate in sea water or the urine flow in fresh water is discussed.
Discrimination Between Movements of Eye and Object by Visual Interneurones of Crickets
Authors: Palka John
Published: April 2021

One large neurone on each side of the cervical and thoracic ventral nerve cord of crickets responds to object motion anywhere in the visual field of the ipsilateral compound eye, but not to the forced or voluntary movement of the eye itself. This discrimination between self-movement and object-movement is accomplished by an inhibitory mechanism mediated by the same eye. Inhibition must be present because a potent moving stimulus becomes ineffective if presented during a forced eye movement. Its visual origin is demonstrated in two ways : (a) abolishing all known mechano-sensory feedback does not disrupt the mechanism, but (b) alteration of visual conditions does so in a predictable way. Sweeping the eye past a complex visual environment suppresses the neurone’s response to a concurrently or subsequently presented moving target, whereas the same movement past a simplified or homogeneous environment produces little or no inhibition. Responses to eye movement itself are greatly enhanced in appropriately simplified visual fields, reinforcing the conclusion that the inhibition preventing response in complex fields is of visual origin. Suggestive evidence for an additional inhibitory mechanism associated with voluntary movement is presented.
Energetics of Ciliary Movement in Sabellaria and Mytilus
Authors: Sleigh M. A. , Holwill M. E. J.
Published: April 2021

High-speed cinephotography has been used to study the movements performed by compound cilia from the segmental gills of Sabellaria and from the abfrontal face of the gill filaments of Mytilus. The two types of cilium have distinctly different beat patterns. Equations are derived which allow the calculation of the energy necessary to overcome viscous resistance during the effective and recovery strokes of a cilium in terms of its dimensions and angular frequency. In Sabellaria cilia the energy needed to overcome viscous forces is greater for the effective stroke than for the recovery stroke, but the reverse is true for Mytilus abfrontal cilia. Estimates of the work done to overcome elastic forces are probably too high, but it appears that the elastic work done in the recovery stroke is greater than that in the effective stroke for cilia of both types if the stiffness remains constant throughout the beat. The energy released if each fibrillar arm causes the breakdown of one ATP molecule per beat cycle is greater than that required to overcome viscous resistance to ciliary motion.
The Site of Synaptic Activity and Impulse Initiation in an Identified Motoneurone in the Crab Brain
Authors: Sandeman D. C.
Published: April 2021

Recordings with an extracellular focal electrode have been taken from different points along the length of an identified motoneurone in the crab brain. Measurements of changes in the conduction velocity, wave-form and amplitude of orthodromic and antidromic spikes show that the site for impulse initiation is separated from the synaptic site by about 300 μm of axon which does not actively propagate spike potentials. The regenerative axon spike invades this non-excitable region electrotonically, the current being focused at two points: one close to the synapse and one near the impulse-initiating site.
The Orientation of Plaice Larvae (Pleuronectes Platessa L.) in Water Currents
Authors: Arnold G. P.
Published: April 2021

An apparatus is described to study the response of fish larvae to water currents. Close to the wall of the water tunnel all pelagic larval stages of the plaice showed a typical rheotropic response. Vector analyses of orientation showed that the response occurred only within 3 cm. from the wall and was absent in midwater. Although the ability to swim against the current increased with age, significant upstream movement only appeared in stage III larvae. Laterally flattened stage IV larvae were less able to swim upstream, but on touching the bottom lay on their sides and showed the behaviour of fully metamorphosed stage V larvae and older fish. In dim light ( < 2·5 m. candles) orientation to the current at the side of the tank also disappeared, but observations with an infra-red viewer and source showed that larvae which touched the wall in the dark could still orientate. It was concluded that the mechanism of the rheotropic response was primarily visual, although it could also be produced by tactile clues. There was no evidence that larvae could respond to the velocity gradients at the tank wall.
Gill Dimensions for Three Species of Tunny
Authors: Muir B. S. , Hughes G. M.
Published: April 2021

Measurements of gill dimensions have been made for many species of fish (e.g. Byczskowska-Smyk, 1957, 1958, 1959; Gray, 1954; Hughes, 1966; Price, 1931; Saunders, 1962; Hughes & Morgan, 1969) with the purpose of estimating the total area of the respiratory surface. Of these, only Price (1931) and Hughes & Morgan (1969) have made a serious effort to determine the relation between size and area within single species. Price reported that for Micropterus dolomieu the total area was related to body weight by the power of 0·78. For the roach and several other species, Hughes and Morgan have found that the relationship is closer to the power of 0·9. For the large number of species ranging from ‘sluggish’ to ‘active’ that he examined, Gray (1954) reported about an order of magnitude of range in the total gill area per gram of fish, but specimen size varied considerably. I. E. Gray (personal communication to G.M.H., 1959) has pointed out that it is important to compare fish of approximately the same size. In his 1954 paper he included Scomber scombrus and Gymnosarda alleterata (= Euthynnus alletteratus) and has also reported (personal communication to G. M. H.) data on the blackfin tuna and the yellowfin tuna. Except for this preliminary work, few studies appear to have been reported on members of the genus Thunnus, which is of considerable interest as it includes some of the largest and most active teleosts.
Sound Production in A Brazilian Cicada
Authors: Aidley D. J.
Published: April 2021

Some aspects of the physiology of sound production in the Brazilian cicada Fidicana rana Walker have been investigated. Three types of natural song are described. Singing can also be induced by electrical stimulation of the head. The tymbal muscles are neurogenically activated and contract alternately. The directional properties of the sound field produced by clicking of the tymbal are described, and the physical properties of the system necessary to produce this directionality are discussed. Removal of the abdomen does not decrease the sound intensity during song produced by electrical stimulation, hence it is concluded that the abdominal air sac does not act as a resonant chamber. The means whereby the sound intensity is varied are discussed. A brief account is given of the occurrence of the different types of song in the natural habitat.
Sound Reception in the Brazilian Cicada Fidicina Rana Walk*
Authors: Enger Per S. , Aidley David J. , Szabo Thomas
Published: April 2021

Sound reception in the Brazilian cicada Fidicina rana has been studied by recording the electrical activity in the auditory nerve in response to various sound stimuli. The highest sensitivity to pure tones is in the frequency range of 6-9 kHz. A considerable and rapid adaptation occurs. The response to trains of clicks consists of a series of compound action potentials. At repetition rates above loo/sec. this response also shows adaptation. The response to the natural continuous song of the cicada is not very different from the response to trains of artificially produced clicks. In the two other types of natural song the adaptation of the auditory response is circumvented. Thus the response to the ‘zeep’ call (during which the intensity of consecutive cficks increases) consists of a series of compound action potentials of about the same amplitude, and the response to the distress call consists of a short burst of action potentials for each burst of clicks. It is suggested that these songs therefore constitute very effective methods of intraspecific signalling.
A Functional Analysis of the Aquatic and Aerial Respiratory Movements of An African Lungfish, Protopterus Aethiopicus, with Reference to the Evolution of the Lungventilation Mechanism in Vertebrates
Authors: McMahon B. R.
Published: April 2021

Recent palaeontological evidence (Jarvik, 1967; White, 1966) indicates that the Dipnoi should be regarded as a specialized group of fishes, which have been structurally different from the Rhipidistia (now thought to have included the prototetrapods) for as long as the fossil record can yet show. However, the homology of the dipnoan lung with that of the tetrapod, and the similarities of organization and development between living Dipnoi and Amphibia, might indicate a closer relationship between the two groups than can be revealed by palaeontological studies. The level of organization seen in the living Dipnoi is not thought to be basically different from that of the Devonian forms and a study of the physiology of these animals must expand our knowledge of the development of vertebrate physiological mechanisms. Since the Dipnoi are adapted to a habitat very similar to that in which the first terrestrial verte-brates are thought to have evolved, and since they possess functional aerial and aquatic respiratory systems, a study of respiratory function in these animals may help to elucidate the manner in which the ancestral tetrapods became able to colonize the terrestrial habitat.
Structure of the Retinae of the Principal Eyes of Jumping Spiders (Salticidae: Dendryphantinae) in Relation to Visual Optics
Authors: Land M. F.
Published: April 2021

The retinae of the principal (AM) eyes of jumping spiders contain four layers of receptors, one behind the other with respect to the incident light. The distribution of receptors in each layer has been determined. The deepest layers (1 and 2) cover the whole area of the retina, and have the greatest density of receptors. The minimum receptor separation is 1.7 μm., or 11 min. visual angle. The more superficial layers (3 and 4) are confined to the central region of the retina. In layers 1, 2 and 3 the rhabdomere-containing segments are rod-shaped, and are parallel to the incident light. In layer 4 they are ovoid, and are oriented approximately at right angles to the light. At the first optic glomerulus the primary fibres from each receptor layer appear to terminate in separate regions of neuropile. The focal lengths, radii of curvature and refractive indices of the lenses of the principal and side eyes have been measured. For the principal eyes, estimates have also been made of the diffraction limit, the depth of focus, and the magnitudes of chromatic and spherical aberration. The normal position of the image in the eye was found by ophthalmoscopy. For blue-green light, the best image of distant objects is formed on the next-to-deepest layer (2). The deepest layer (1) is conjugate with a plane about 2 cm. in front of the animal for blue-green light, or with infinity for red light, because of the eye’s chromatic aberration. Two theories are offered to account for the retinal layering. Either the spider uses different layers to examine maximally sharp images of objects at different dis tances; or each layer exploits the sharpest image of distant objects, but for light of different wavelengths. Optical considerations indicate that either theory is possible, but the seconds (wavelength) theory is the more probable, because jumping spiders are known to possess colour vision. It predicts that layer 1 receptors contain red-sensitive, layer 2 blue-green sensitive and layer 3 violet-ultraviolet Sensitive pigments. The structural peculiarities of the most superficial layer (4), and the fact that it is not conjugate with any plane in front of the animal for any visible wavelength, suggest that it is not resolving an image, but performing some other function. Reasons are given for thinking that this might be the analysis of the pattern of polarization of skylight.
Movements of the Retinae of Jumping Spiders (Salticidae: Dendryphantinae) in Response to Visual Stimuli
Authors: Land M. F.
Published: April 2021

Movements made by the principal eyes of jumping spiders (Phidippus and Metaphidippus spp.) have been investigated using an ophthalmoscopic technique which permits simultaneous observation and stimulation of the retinal surface. The eye-movements are produced by six muscles. Four are attached to the carapace, and displace each retina latero-medially and dorso-ventrally. The remaining pair are thin bands of muscle which encircle the eye-tube. TThe nerve supplying these muscles contains only six axons. Each axon terminates in one of the six muscles. The nerve supplying these muscles contains only six axons. Each axon terminates in one of the six muscles. Four types of eye-movements are observed. These are spontaneous activity, saccades, tracking and scanning. All movements are usually conjugate. Spontaneous activity consists of a very variable, periodic side-to-side motion of the retinae. It is associated with states of high excitability, and occurs whether or not there is any structure in the field of view. Saccades occur when a small stimulus (e.g. a dark dot) is presented to, or moved upon, the retinae of either the principal eyes or the antero-lateral eyes. In a saccade the retinae move towards the image of the target so that they come to rest with their central regions fixated on the target. If the target moves the retinae track it, maintaining central fixation. Scanning normally follows a saccade. It consists of an oscillatory, side-to-side movement of the retinae across the stimulus, with a period of 1-2 sec., and a simultaneous torsional movement in which the retinae partially rotate about the visual axes, through an angle of approximately 50° and with a period of 5-15 sec. Jumping spiders distinguish other jumping spiders from potential prey by the geometry of their legs. It is suggested that scanning is a pattern-recognition procedure in which the torsional movements are concerned with the spatial alignment of line or edge detectors, and the horizontal component with providing relative motion between these detectors and the stationary stimulus.
Rapid Contractions and Associated Potentials in A Sand-Dwelling Anemone
Authors: Pickens Peter E.
Published: April 2021

Two kinds of electrical potentials can be recorded from the surface of the. retractor muscle of the anemone, Calamactis, during rapid contraction. These are large muscle action potentials and smaller pulses which are thought to be nerve spikes The latter resemble nerve impulses of higher organisms in that they are all-or-none and of short duration. A nerve spike follows each of a pair of electrical stimuli, but the muscle potential and contraction occur only after the second shock, indicating that facilitation is required at the neuromuscular junction. The size of the muscle potential and of the contraction are correlated with the interval between paired electrical stimuli. Maximum size is reached when stimuli are zoo msec. apart even though the minimum effective interval is 30 msec. A muscle potential precedes contraction only along the upper part of the retractor muscle and this is the part that contracts rapidly during the withdrawal response. The lower retractor does not contract. Conduction velocity along the upper retractor is higher than along the lower. The histological correlate of rapid conduction is a nerve net with large, long, longitudinally oriented fibres. The refractory period of the conducting system of the upper retractor is shorter than that of the lower retractor. Consequently, spread of excitation toward the aboral end is limited if paired stimuli are further apart than 250-300 msec. A mechanical stimulus which is just strong enough to elicit a withdrawal response evokes a single muscle potential of maximum size, suggesting that two nerve impulses closer together than 200 msec. precede the muscle potential. Stronger mechanical stimuli evoke a burst of muscle potentials.
Reflex Organization in the Swimmeret System of the Lobster
Authors: Davis W. J.
Published: April 2021

The intrasegmental feedback reflexes in the swimmeret system of the lobster Homarus americanas were activated while recording the responses from the swimmeret nerves and muscles. Two main sources of sensory feedback were identified; proprioceptors in the coxal region of the swimmeret, and sensory setae on the edges of the two rami of each swimmeret. The reflexes activated by these inputs are described. Reflexive feedback from the powerstroke movement to the powerstroke excitatory motor neurones is positive, further reinforcing the movement. Intrasegmental reflexes capable of independently initiating or terminating the powerstroke activity are absent, however. Therefore the powerstroke movement of each cycle can begin and end only in response to a purely central nervous motor command. It follows that the intrasegmental swimmeret reflexes are incapable of contributing to the periodicity seen in the motor output pattern which underlies swimmeret beating. In addition to strengthening the powerstroke, the intrasegmental reflexes strengthen the linkage between the powerstroke and the returnstroke within each movement cycle. The reflexes may also reinforce the reciprocity between excitor and inhibitor axon activity to the main powerstroke and returnstroke muscles. It is shown, however, that these three features of the motor output pattern are programmed into the CNS independently of the sensory feedback. The intrasegmental reflexes thus act as subservient amplifying devices for cyclic motor patterns which are produced independently by purely central nervous mechanisms.
Active Transport and Sodium Fluxes at Moult in the Amphipod, Gammarus Duebeni
Authors: Lockwood A. P. M. , Andrews W. R. H.
Published: April 2021

The sodium fluxes of individual Gammarus duebeni, which moulted in sea water, have been followed daily from the morning following moult for at least 6 days. Sodium influx from sea water declined from 15·1µM/animal/hr. on the first morning after moult to 1·7 µM/animal/hr. by the tenth day after moult. Sodium influx from 10 mM/l. NaCl plus sucrose solution isotonic with sea water declines from 4·48 µM/animal/hr. to 0·14 µM/animal/hr. in inter-moult animals. Thionine inhibits over 90% of the influx from 10 mM/l. NaCl plus isotonic sucrose on the first day after moult, and this, together with other evidence, suggests that the major part of the influx from this medium is due to active sodium uptake. The rate of active uptake is comparable with, or faster than, the rate of uptake by animals acclimatized to fresh water. The influx occurs primarily across the body surface. It is suggested that the high level of sodium uptake is associated with the water uptake which occurs at moult.
The Input-Output Organization of A Pair of Giant Neurones in the Mollusc, Anisodoris Nobilis (Macfarland)
Authors: Gorman A. L. F. , Mirolli M.
Published: April 2021

Each of the two gastro-oesophageal ganglia of the nudibranch mollusc, Anisodoris nobilis, contains one giant neurone (G cell) whose axon is directed toward the oesophagus in the gastro-oesophageal nerve. In the absence of stimulation the G cells are normally silent. However, they receive inhibitory and excitatory synaptic inputs from more central ganglia and a predominantly excitatory input from the periphery. The inputs from the central ganglia are bilaterally distributed to both G cells, whereas the inputs from the periphery are limited to the ipsilateral G cell. Intracellular stimulation shows that there is no interaction between the G cells, nor between the G cell and other cells in the same or contralateral gastro-oesophageal ganglia. The axon of the G cell makes synaptic contact with a series of peripheral cells (P cells). In most P cells the post-synaptic potential elicited by intracellular stimulation of the G cell is constant in amplitude and latency and probably results from a unitary monosynaptic contact. Intracellular stimulation shows that the P cells are not connected to the G cell. The P cells are inter-connected by low-resistance electrotonic junctions which allow slow potentials of either polarity to spread between cells. These junctions exist between distant as well as adjacent peripheral neurones. Our results show that the G cell functions as a command interneurone for an aggregate of electrically interconnected peripheral neurones.