bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Comparative Study Of The Double Motor Innervation In Marine Crustaceans
Authors: Wiersma C. A. G. , Harreveld A. Van 
Published: April 2021

ABSTRACT
A double motor innervation has been shown for several muscles of marine crustaceans. The adductors of the claws of Randallia and Blepharipoda and the adductor of the dactylopodite of the walking leg of Cancer were studied physiologically.
The two motor axons which innervate these muscles have a different diameter (ratio 1·4 : 1). Stimulation of the thick fibre causes a response, which, though it is not always faster than the response of the thin fibre, must be considered as a “fast” contraction. In Randallia and in Blepharipoda the slow contraction is higher than the fast with frequencies of less than ±50 per sec., in Cancer with frequencies less than 100 per sec.
The action currents of the two kinds of contraction are different. Both show facilitation, but under the same conditions of stimulation the fast-action currents are higher. The first stimulus of the thick fibre causes an action current top which is clearly distinguishable, the action currents of the slow contraction show up only after a number of stimuli. Even when the mechanical reaction on stimulation of the thick fibre is smaller than on similar stimulation of the thin fibre, the action currents are higher in the first case.
A single impulse in the thick fibre does not cause a contraction, but sets up a muscle-action current. The chronaxie of this action current in Blepharipoda and Randallia is 0·8σ and is about the same as that found for the action current of the nerve. Two impulses in the thick fibre may cause a mechanical response, as is shown by summation experiments. The pseudo-chronaxie of this contraction was measured as 3·5 σ. The second action current shows facilitation, when it follows the first within 1 sec.; a mechanical reaction results with summation intervals of two stimuli of less than 10 σ. The facilitation of the action current increases with decrease of the time interval between the two impulses ; with the shortest intervals that give summation the resulting action current is a smooth high spike.
The Role Of The Fins In The Equilibrium Of The Swimming Fish
Authors: Harris J. E. 
Published: April 2021

ABSTRACT
The paired fins of fishes are largely concerned with the production of vertical forces, and thus principally affect the pitching (rising and diving) equilibrium. In the sharks the pelvic fins increase to a small extent the static stability for pitching movements. Nevertheless, the relatively large area and forward position of the pectoral fins preponderates over the influence of the pelvics on the pitching stability, so that the contribution of the latter is very small. This is borne out by amputation experiments. In the bony fishes, the development of the actinopterygian fin leads to a much greater mobility of the fins. In consequence, the pelvic fins of the bony fishes exhibit a considerable adaptive radiation. In the percoid fishes the use of the pectoral fins as brakes produces a lift as well as a drag force. It is shown that the neutralization of this lift force by a downward force produced by the pelvic fins necessitates the forward migration of the latter. If this migration did not take place, the fish would either tilt upwards or rise bodily during the stop. The dynamical basis for this migration of the paired fins is considered in an approximate mathematical treatment of the equilibrium during the stop. This hypothesis is confirmed by amputation experiments, and also by the occurrence of a convergent fin migration in the Coelacanthidae. The absence of the forward pelvic fin migration in flying fishes also affords indirect support. There is no evidence to suggest that the pelvic fins can function as bilge keels, though they may be used actively to produce a rolling moment.
The Colour Changes In Lizards, Particularly In Phrynosoma
Authors: Parker G. H. 
Published: April 2021

ABSTRACT
The activities of the melanophore system of Phrynosoma in comparison with that of Chamaeleo may be stated categorically in the following way.
I. The blanching of Phrynosoma blainvillii is due
(1) to the action of its concentrating nerve-fibres on its melanophores, (2) to the action of a hydrohumour, probably adrenalin, on the same cells, (3) to the direct response of these cells to darkness, and (4) to high temperatures.
II. The blanching of Chamaeleo is due to the first, third, and fourth of these factors. Whether the second factor is effective in this lizard is not yet determined.
III. The darkening of Phrynosoma is due
(5) to the action of a pituitary neurohumour on its melanophores, (6) to the direct response of these cells to strong light, and (7) usually, to low temperatures.
There are no dispersing nerve-fibres known in Phrynosoma.
IV. The darkening of Chamaeleo is due to the sixth and probably to the seventh of these factors. This lizard presents strong indications of possessing dispersing nerve-fibres. Whether it darkens from a pituitary neurohumour or not is unknown.
A Manometric Respirometer for Snails
Authors: Wells G. P. 
Published: April 2021

ABSTRACT
In the course of an investigation into the physiology of the edible snail (Helix pomatia L.), it became necessary to measure the respiration individually of large numbers of animals. A system in which CO2-free air was passed over the animals and then through baryta was tried but rejected because the snails apparently dislike currents of air, tending to withdraw into their shells. Analysis of gas samples from containers in which the animals respire was not employed, partly because the accumulation of CO2 involved may conceivably affect the respiratory exchanges, and partly because the accuracy of the method is insufficient except in very experienced hands. It was therefore decided to adopt a manometric method.
The Absorption of Fluid from the Tracheal System of Mosquito Larvae At Hatching and Moulting
Authors: Wigglesworth V. B. 
Published: April 2021

ABSTRACT
During development the tracheal system of insects is at first filled with fluid. About the time of hatching from the egg and at each subsequent moult this fluid is absorbed into the tissues. The mechanism of absorption was studied in a number of insects, and earlier work on the subject reviewed, by Sikes & Wigglesworth (1931), who concluded that although secretory activity might be responsible for the presence in the tracheal system of a fluid which could be absorbed by osmosis, the final absorption was probably brought about by the osmotic pressure of the blood. At the suggestion of Prof. A. Krogh, who has taken an active interest throughout this work, the problem has been reinvestigated with a view to differentiating the part played by secretion.
The Humidity Gradient at the Surface of a Transpiring Leaf
Authors: Ramsay J. A. , Butler C. G. , Sang J. H. 
Published: April 2021

ABSTRACT
An hygrometer and an evaporimeter, capable of investigating atmospheric conditions over small areas close to the surface of a leaf, are described. In the case of rapidly transpiring leaves in a slow air stream a humidity gradient has been detected up to a height of 1.2 cm.
Host-Finding by Insect Parasites
Authors: Laing J. 
Published: April 2021

ABSTRACT
Experiments are described in which Trichogramma females were provided with Sitotroga eggs arranged at various distances from 0·05 to 0·40 in. The frequency with which the parasite found the neighbouring egg varied inversely with the distance between the eggs. The relation between frequency of contact and distance between the hosts depends chiefly, but not entirely, on chance. The rate of finding the eggs varied inversely with the distance between them. By consideration of the conditions of the experiments, this relation between the rate of finding and the distance between the eggs is seen to indicate that the Trichogramma does not seek at random over the whole area available for movement but restricts its search to the neighbourhood of hosts. From experiments with eggs of four sizes it is shown that frequency of neighbouring contact is correlated positively with the size of the eggs. The influence of size is largely mechanical ; but not entirely, for small eggs of Sitotroga are found less efficiently in proportion to their size than are larger eggs. When provided simultaneously with hosts of two different sizes, a Trichogramma finds more of the larger than of the smaller hosts. If the hosts are arranged alternately, the amount of selection that occurs by finding depends entirely upon the relative sizes of the eggs. If they are arranged in separate groups, however, relatively more of the larger eggs are found.
Tracheal Pulsation in the Flea
Authors: Herford G. M. 
Published: April 2021

ABSTRACTThe phenomenon of tracheal pulsation has been demonstrated in three different species of fleas. It is shown to be independent of the other body rhythms, such as those of the heart and gut. Experiments are described showing the effect of oxygen, carbon dioxide, evacuation and of sectioning the central nervous system. Three theories are put forward to explain the phenomenon, and their relative merits are discussed.
The Spherical form of the Mammalian Erythrocyte
Authors: Ponder Eric , Neurath Hans 
Published: April 2021

ABSTRACT
The most suggestive observation which we have regarding the remarkable disk-sphere transformation which occurs when mammalian red cells in saline are enclosed between slide and coverslip is that the velocity and extent of the shape change depends on the distance between the surfaces, and upon whether or not both surfaces are wetted by the suspension medium (Ponder, 1929). Thus the transformation occurs rapidly and completely between two glass surfaces 50μ. apart, but slowly and incompletely between two glass surfaces 1 mm. apart, and paraffining of both surfaces, or the substitution of surfaces unwetted by saline, prevents the shape change completely. That the transformation is due to electrostatic charges on the surfaces, pressure,2 or diffusion of alkali from the glass, has been disproved experimentally (Ponder, 1929, 1936), and the only suggestion which still remains is that the surfaces have an orienting effect, of an obscure nature, on a “liquidcrystal” structure in the red-cell envelope.
Regulation of Amphibian Gastrulae with Added Ectoderm1
Authors: Waddington C. H. 
Published: April 2021

ABSTRACT
If a young Urodele gastrula is cut or constricted into two along the frontal plane, so that the dorsal and ventral halves are separated, the dorsal part contains the whole organization centre but an abnormally small amount of presumptive ectoderm; nevertheless, as Spemann (1903) and Ruud & Spemann (1922) showed, it regulates to form a complete embryo of normal proportions but of small absolute size. Schmidt (1933) demonstrated the same thing for Anuran gastrulae. Thus an absence of ectoderm causes modification of the normal development of the organization centre. We have much less information of the effect of increase in the proportion of presumptive ectoderm. Bruns (1931) added fairly small pieces of ectoderm to entire gastrulae, and obtained embryos apparently indistinguishable from normal ; but the amounts added were so small that one could not expect easily visible effects. In the experiments to be reported here, very much larger quantities of ectoderm were added to normal gastrulae, and, as will be shown, it was found that the presence of this added material caused an increase in size of the invaginated roof of the gut, so that an embryo of normal proportions but increased size was developed.
The Relative Toxicity of Salts of Lead, Zinc and Copper to the Stickleback (Gasterosteus Aculeatus L.) and The Effect of Calcium on the Toxicity of Lead and Zinc Salts
Authors: Jones J. R. Erichsen 
Published: April 2021

ABSTRACT
Lethal limits of concentration are determined for lead, zinc and copper for the three-spined stickleback (Gasterosteus aculeatus L.). The addition of calcium salts to solutions of lead nitrate or zinc sulphate reduces the toxicity of these salts to Gasterosteus. 50 mg. per 1. of calcium (as nitrate or chloride) is sufficient to annul the toxicity of a 1 × 10−6 g. per c.c. solution of lead or a 2 × 10−6 g. per c.c. solution of zinc. The reactions of the fish in the solutions with and without calcium are compared, and the respiratory symptoms are described with the aid of graphs illustrating the variation in respiration rate during the survival time. It is shown that a running supply of “hard” tap water containing approximately 50 mg. per 1. of calcium as calcium bicarbonate is harmless to the minnow, Phoxinusphoxinus (L.) and to the stickleback, when there is added to it the maximum amount of lead that it can hold in solution (7 ×10−7g. per c.c.). This concentration of lead in soft water is fatal to Gasterosteus in 3812 hr. The same amount of calcium renders a 10 × 10−6 g. per c.c. solution of lead harmless to the goldfish, Carassius auratus (L.). It is concluded that, in the presence of sufficient calcium, the interaction between the lead, or zinc, and the mucus secreted by the fish does not take place. This conclusion was endorsed by experiments in vitro on the slime secreted by the eel, Anguilla anguilla (L.). The application of these results to the pollution of natural waters by effluents from lead and zinc workings is briefly discussed.
The Mechanism of Locomotion in the Leech (Hirudo Medicinalis Ray)
Authors: Gray J. , Lissmann H. W. , Pumphrey R. J. 
Published: April 2021

ABSTRACT
Considerable uncertainty still exists concerning the nature of the mechanism which maintains the normal locomotory rhythm of terrestrial animals. Two types of theory have been advanced: (i) That the rhythm is determined by the existence of a closed chain of peripheral reflexes, each phase of a complete locomotory cycle setting up automatically the particular pattern of peripheral stimulation requisite for the elicitation of the succeeding phase in the cycle, (ii) That the rhythm is, fundamentally, a property of the central nervous system which is, however, susceptible to modification or extinction by peripheral stimulation.
The Rates of Conduction of Nerve Fibres of Various Diameters in Cephalopods
Authors: Pumphrey R. J. , Young J. Z. 
Published: April 2021

ABSTRACT
The rates of conduction of nerve fibres of Sepia and Loligo varying from 30 to 718μ in diameter have been estimated from records of their action potentials. The limits of conduction velocity were found to be 2.2-22.8 m./sec. at 20° C. Although the fibres examined have different functions, and come from animals which differ considerably in structure and mode of life, yet the conduction rates of all of them can be approximately expressed as a single function of the diameter. These fibres, therefore, do not differ greatly from each other in any respect but size. Calculation of the regression coefficient of the log. of the conduction rate on the log. of the diameter of the fibres shows that the rate increases with the power 0.614+0.027 of the diameter. On account of various sources of error however the exact relation does not necessarily lie within these limits, but it is not likely to be very far from the square root. The possession of giant fibres produces a significant saving of time for the animal, it being calculated that the reaction time of a squid is about half that of a similar animal without giant fibres. The presence of rapidly conducting fibres is probably also an advantage in that it decreases the discrepancies between the times of contraction of parts of the mantle at varying distances from the central nervous system. In Loligo there is a graded series of fibres with the larger in the longer nerves, and this is apparently a further device for ensuring more nearly simultaneous contraction. The relative thickness of the myelin-like sheath increases from about 1% of the diameter of the axon in cephalopods to 5% in Crustacea and annelids and 25% in vertebrates: the conduction velocity of fibres of a given size also increases in the same series. This parallelism provides strong support for the view that the layer of oriented lipoids increases the velocity of propagation of the nerve impulse in proportion to its thickness.
Proprioception in Insects
Authors: Pringle J. W. S. 
Published: April 2021

ABSTRACTConcentrations of hair sensilla have been noted by a number of authors in the joints of the insect body and limbs. Special groups of such sensilla in the form of “hair plates” are described from three positions on the legs of Periplaneta americana. The hairs of the hair plates are mechanical sense organs with a slow rate of adaptation. In life the hairs are excited by a fold of the intersegmental membrane, the excitation varying with the position of the joint. It is suggested that these and similar structures in other parts of the bodies of insects act as “position” sense organs.
The Posture of the Abdomen during Locust Flight: Regulation by Steering and Ventilatory Interneurones
Authors: Baader Andreas 
Published: April 2021

ABSTRACT
Tethered flying locusts (Locusta migratoria) make correctional steering movements with the abdomen when stimulated with a moving artificial horizon and integrated wind jet, simulating deviation from a straight course. Neurones in the metathoracic and first abdominal neuromeres of the metathoracic ganglion have been characterized morphologically and physiologically. The selective stimulation of these cells causes movements of the abdomen. One group of neurones responds directionally to visually perceived horizon movements and is excited by wind on the head. Some of these neurones are rhythmically activated at the flight frequency while others receive tonic drive from the flight oscillator. Electrical depolarization results in bending of the abdomen; the direction of this movement is always compatible with compensatory steering. Interneurones which are active during the expiration phase of ventilation also contribute to the posture of the abdomen in flight. They are not visually responsive but their selective inhibition at the onset of flight activity helps to bring the abdomen into flight posture. Some of these Interneurones are modulated at the flight frequency. The efficiency of cooperation between different sets of Interneurones in producing behavioural patterns and the signficance of single neurone stimulation are discussed.
Glycolytic Enzyme Binding and Metabolic Control in Estivation and Anoxia in the LandSnail Otala Lactea
Authors: Brooks Stephen P. J. , Storey Kenneth B. 
Published: April 2021

ABSTRACTThe mechanisms controlling glycolytic rate were examined in foot muscle of the terrestrial snail Otala lactea (Müller) (Pulmonata, Helicidae), during short and long periods of estivation and anoxia. Binding associations between glycolytic enzymes and the particulate fraction of the cell were assessed in both states. The percentage of enzyme activity bound to particulate matter decreased significantly over the short term (4 days estivation and 14·5 h anoxia); significant changes were seen for hexokinase (HK), phosphofructokinase (PFK), aldolase and lactate dehydrogenase (LDH) in estivation and, for these enzymes plus triosephosphate isomerase and pyruvate kinase (PK), in anoxia. Over the longer term in estivation (22 days) and anoxia (45 h), enzyme binding returned to control values. Tissue content of fructose-2,6-bisphosphate, a potent phosphofructokinase activator, decreased under all experimental conditions. Total glycogen phosphorylase activity decreased during short-term anoxia (14·5 h) and during long-term estivation (22 days), but the percentage of the active a form decreased significantly during anoxia only. Significant changes in the maximal activities of several enzymes were observed during both estivation and anoxia. Decreases in the maximal activity of HK, PFK, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase (PGK) and LDH were observed during long-term estivation. Increases in PGK and PK maximal activity in short-term anoxia and aldolase and PGK in long-term anoxia were also observed. These results suggest that changes in glycolytic enzyme binding may be part of an immediate mechanism used to cause a rapid decrease in glycolytic flux and initiate glycolytic rate depression, which also includes a reduction of fructose-2,6-bisphosphate content and decreased glycogen phosphorylase activity. In the long term, however, control of snail glycolytic rate is reorganized, so that enzyme binding associations revert to the control values. In the long term, then, control is mediated by lower fructose-2,6-bisphosphate concentrations and, during estivation, also by a decrease in maximal enzyme activities.
Effects of Hypoxia and Drugs on the Cardiovascular Dynamics of the Atlantic HagfishMyxine Glutinosa
Authors: Axelsson Michael , Farrell Anthony P. , Nilsson Stefan 
Published: April 2021

ABSTRACTCardiac output, ventral and dorsal aortic blood pressure and heart rate were recorded simultaneously in unanaesthetized hagfish, Myxine glutinosa L. Mean cardiac output was 8.7 ml min−1 kg−1 and mean heart rate 22.3 beats min−1. The absence of beat-to-beat oscillations in heart rate was consistent with the lack of an extrinsic cardiac innervation in hagfish. Mean blood pressures were 1.04 kPa (ventral aorta) and 0.77kPa (dorsal aorta).Injection of adrenaline into the caudal vein significantly increased cardiac output, stroke volume, heart rate and blood pressures of both aortas. Peak cardiac output was close to 25 ml min−1 kg−1. Injection of the β-adrenoreceptor antagonist sotalol decreased resting heart rate significantly. We conclude that endogenous catecholamines from chromaffin cells of the heart are instrumental in the regulation of cardiac function in Myxine.Injection of acetylcholine had little direct effect on the recorded cardiac variables, but caused marked branchial vasoconstriction. Heart rate increased as the pressor response subsided. The cholinergic antagonist atropine had no effect on any of the resting parameters.Injection of adenosine had no direct cardiac effects but reduced the systemic vascular resistance.Severe hypoxia (kPa for 15–35 min) had very little effect on the cardiovascular variables recorded. The remarkable ability of the hagfish heart to maintain normal cardiac output during severe hypoxia is discussed with respect to the anaerobic pumping capacity of the heart.Pump-perfused, in situ gill preparations were used to examine branchial vasoactivity. Acetylcholine and adrenaline produced dose-dependent vasoconstriction, whereas isoprenaline, noradrenaline and adenosine dilated the branchial vasculature.
An Analytical Electron Microscopy Study of Iron-Rich Teeth from the Butterflyfish (Chaetodon Ornatissimus)
Authors: Sparks N. H. , Motta P. J. , Shellis R. P. , Wade V. J. , Mann S. 
Published: April 2021

ABSTRACTIron is known to be a common constituent of vertebrate teeth, yet little is known about the form it takes or the extent to which it modifies the structural properties of the tooth. Analytical electron microscopy was used to study the iron-rich tooth cap of the butterflyfish Chaetodon ornatissimus Cuvier, 1831. Images of thin sections of the tooth cap showed three distinct layers of hydroxyapatite crystals; a densely packed cuticle, a crystallographically organized superficial enameloid and a randomly oriented inner enameloid. Energy dispersive X-ray analysis (edXa) showed that iron was concentrated in the cuticular layer of the tooth cap, the concentration increasing to a maximum at the tip. Elemental analysis showed the level of calcium to be inversely related to iron concentration. An identical relationship was found for synthetic iron-doped hydroxyapatite. The implications of these results for the functional role of iron in the tooth caps are discussed.