bluuebunny/crossref_metadata_2025_split huggingface dataset:
Circulatory Mechanics in the Toad Bufo Marinus: II. Haemodynamics of the Arterial Windkessel
Authors: Gibbons Carol A. , Wick Robert E. Shad 
Published: April 2021

ABSTRACT
This study examines the importance of vascular elasticity to arterial haemodynamics in a poikilothermic vertebrate. Pulsatile blood pressure, flow and vessel diameter were recorded at several locations within the arterial tree of the toad, Bufo marinus. We then determined the dynamic elastic modulus, the pulse wave velocity and the hydraulic impedance characteristics of the aorta. The relatively low heart rate and short arterial tree, and a pulse velocity of about 2.5ms−1, combine to give a transit time for the pressure pulse through aorta that is only 3% of the cardiac cycle. Consequently, wave propagation effects seen in mammals, such as peripheral amplification, distortion and secondary pressure peaks due to reflections, are not apparent. Instead, the aorta acts as a simple Windkessel and inflation by the heart occurs almost simultaneously throughout. Pressure waveforms are nearly identical at proximal and distal locations, and flow pulsatility is reduced progressively through the elastic aorta.
Dragonfly Flight: Power Requirements at High Speed and Acceleration
Authors: May Michael L. 
Published: April 2021

ABSTRACT
Most studies of insect flight deal primarily with hovering or with forward flight at constant, moderate speed. This paper reports investigations of flight characteristics that are especially relevant to the performance of dragonflies at high and/or changing velocity. Dragonflies were filmed in free flight in the field to determine velocity and acceleration. The power required for repeated acceleration is shown to be large, in some circumstances, relative to the estimated maximum available power and probable top power requirements for steady flight. Distributions of velocity and acceleration, and concomitant power requirements, differ markedly among species, however. In addition, parasite drag was measured in winds of 2–7ms−1 and drag coefficients determined to be about 0.40 at Reynolds number greater than 104. This result implies substantially lower power requirements at high speeds, compared to previous estimates. Other aspects of power output, including the probable magnitude of inertial power, are considered in relation to published data.
Early Life Stages of Carp (Cyprinus Carpio L.) Depend on Ambient Magnesium for Their Development
Authors: Van Der Velden J. A. , Spanings F. A. T. , Flik G. , Bonga S. E. Wendelaar 
Published: April 2021

ABSTRACT
Carp eggs, fertilized in vitro, were allowed to develop in fresh water with magnesium concentrations varying from 0·001 to 0·100 mmol l−1. Magnesium concentrations below 0·010 mmol l−1 seriously impeded carp embryonic development: the incidence of deformed larvae and mortality increased steeply to 100% at water magnesium concentrations of 0·001 mmol l−1. Thus, early life stages of carp require ambient magnesium for survival and successful development. The magnesium and calcium concentrations of the developing eggs were dependent on the ambient magnesium concentration. The uptake of magnesium by eggs decreased and the uptake of calcium increased with decreasing ambient magnesium concentrations. However, the uptake of the sum of these divalent ions seemed to be independent of ambient magnesium concentration. This indicates a competition between magnesium and calcium for (passive) uptake into developing eggs.
Behavioral Analysis of the Escape Response in the Juvenile Lobster Homarus Americanus Over the Molt Cycle
Authors: Cromarty S. I. , Cobb J. S. , Kass-Simon G. 
Published: April 2021

ABSTRACT
Components of the escape response of the American lobster were compared over the molt cycle. Number of tailflips, frequency, duration and distance were measured. Velocity, acceleration, force and work were computed from the above measurements, using time-lapse video-recordings of escaping lobsters. Soft-shelled postmolt lobsters (stage B) traveled further, spent more time tailflipping and performed a larger number of tailflips than hard-shelled premolt lobsters (stage D). Hard-shelled lobsters had a more forceful initial power swim, achieved a higher overall velocity and acceleration and, therefore, produced more forceful swims with greater energy expenditure (measured by work output) than soft-shelled animals. Among hard-shelled lobsters, velocity, acceleration, force and work fell off markedly in the latter part of their subsequent swims as a consequence of the prolonged duration and reduced frequency of these swims. Soft-shelled lobsters sustained their swimming velocity, acceleration, force and work for their entire subsequent swimming response. There are likely to be large molt-related differences in energy metabolism, endocrinology and nerve and muscle physiology which lead to the observed differences in the escape response.
The Whole-Body Withdrawal Response Of Lymnaea Stagnalis I. IdentificatIon Of Central Motoneurones And Muscles
Authors: Ferguson Graham P. , Benjamin Paul R. 
Published: April 2021

ABSTRACT
Two muscle systems mediated the whole-body withdrawal response of Lymnaea stagnalis: the columellar muscle (CM) and the dorsal longitudinal muscle (DLM). The CM was innervated by the columellar nerves and contracted longitudinally to shorten the ventral head-foot complex and to pull the shell forward and down over the body. The DLM was innervated by the superior and inferior cervical nerves and the left and right parietal nerves. During whole-body withdrawal, the DLM contracted synchronously with the CM and shortened the dorsal head-foot longitudinally. The CM and the DLM were innervated by a network of motoneurones. The somata of these cells were located in seven ganglia of the central nervous system (CNS), but were especially concentrated in the bilaterally symmetrical A clusters of the cerebral ganglia. The CM was innervated by cells in the cerebral and pedal ganglia and the DLM by cells in the cerebral, pedal, pleural and left parietal ganglia. Individual motoneurones innervated large, but discrete, areas of muscle, which often overlapped with those innervated by other motoneurones. Motoneuronal action potentials evoked one-for-one non-facilitating excitatory junction potentials within muscle fibres. No all-or-nothing action potentials were recorded in the CM or DLM, and they did not appear to be innervated by inhibitory motoneurones. The whole network of motoneurones was electrotonically coupled, with most cells on one side of the CNS strongly coupled to each other but weakly coupled to cells on the contralateral side of the CNS. This electrotonic coupling between motoneurones is probably important in producing synchronous contraction of the CM and DLM when the animal retracts its headfoot complex during whole-body withdrawal.
Biomechanics of Flight in Neotropical Butterflies: Aerodynamics and Mechanical Power Requirements
Authors: DUDLEY ROBERT 
Published: April 2021

A quasi-steady aerodynamic analysis of forward flight was performed on 15 species of neotropical butterflies for which kinematic and morphological data were available. Mean lift coefficients required for flight typically exceeded maximum values obtained on insect wings under conditions of steady flow, thereby implicating unsteady aerodynamic mechanisms even during fast forward flight of some butterflies. The downstroke produced vertical forces on average 18% in excess of those necessary to support the body weight through the wingbeat, while the upstroke contributed minimal or negative vertical force. Estimated effective angles of incidence (αT of the wings averaged 39° during the downstroke and −22° during the upstroke; spanwise variation in αT was greater than the average difference between half-strokes. Total mechanical power requirements of forward flight averaged 12.5 W kg−1, for the case of perfect elastic storage of whig inertial energy, and 20.2 W kg−1, assuming zero elastic energy storage. Energetic costs of the erratic trajectories during forward flight increased mechanical power requirements by an average of 43%, assuming perfect elastic storage. Fluctuations in horizontal kinetic energy of the center of mass were principally responsible for this dramatic increase. When comparing different species, total mechanical power increased linearly with forward airspeed (assuming perfect elastic energy storage of inertial energy) and scaled with mass0.26 If no elastic energy storage was assumed, mechanical power was independent of airspeed and was proportional to mass0.36. Estimated metabolic rates during flight averaged 22 and 36 ml O2 g−1 h−1, for the cases of perfect and zero elastic storage, respectively.
Note: Mailing address: Smithsonian Tropical Research Institute, APO Miami, FL 34002, USA.
Acidosis (Measured by Nuclear Magnetic Resonance) and Ethanol Production in Anoxic Goldfish Acclimated to 5 and 20°C
Authors: VAN WAARDE AREN , DE GRAAFF INGRID , VAN DEN THILLART GUIDO , ERKELENS CEES 
Published: April 2021

Goldfish acclimated to 20 and 5°C were subjected to anoxia (3 h at 20°C and 18 h at 5°C). The intracellular pH (pHi) and the levels of high-energy phosphate compounds in the epaxial muscle were continuously monitored by in vivo31P-n. m.r. spectroscopy. Free [ADP] was calculated from n.m.r.-measured reactants of the creatine kinase reaction and the creatine kinase equilibrium constant. A rapid initial drop in pHi was followed by a sudden decrease in the rate of development of acidosis. Similar biphasic time courses were observed for the increases in the levels of free ADP and inorganic phosphate and the decrease in phosphocreatine concentration.
In a parallel series of experiments, fish were placed in the flow cell of the n.m.r. probe (outside the magnet) and anesthetized after different anoxic intervals. Metabolites in red muscle, white muscle and blood were then assayed, using classical biochemical techniques. The transition to a less rapid decline in pH appears to be primarily due to a suppression of energy demand and activation of H+ extrusion; ethanol production becomes significant only after longer periods of anoxia. Anoxic exposure has no influence on the kinetic properties of muscle alcohol dehydrogenase, but acclimation of goldfish to low temperature increases alcohol dehydrogenase activity in white muscle.
Note: Present address: PET Center, Academic Hospital, Groningen University, PO Box 30.001, 9700RB Groningen, The Netherlands.
Mechanics of Underwater Locomotion in Diving Ducks: Drag, Buoyancy and Acceleration in a Size Gradient of Specffis
Authors: LOWORN J. R. , JONES D. R. , BLAKE R. W. 
Published: April 2021

1. The effects of accelerational swimming and body size on mechanical energy costs of diving were examined by comparing canvasback (Aythya valisineria Wilson), redhead (A. americana Eyton) and lesser scaup (A. affinis Eyton) ducks (mean body mass 1.275, 1.013 and 0.817kg, respectively) in steady versus unsteady models of locomotion. Steady models assume constant speed, whereas unsteady models incorporate acceleration and deceleration with each propulsive stroke. 2. The surface areas of the ducks increased linearly with body mass (r2=0.96), with all species falling on the same curve. 3. Body drag D of frozen ducks towed under water increased with body mass M and speed U according to the relationship D = −0.946+0.826M+0.614U+0.825U2, r2=0.95. 4. In kinematic analyses, regression curves of percentage of total stroke distance versus percentage of stroke duration did not vary within individuals, sometimes varied between individuals and always varied between species. In diving ducks, analyses of a single sequence per individual and several individuals per species will usually provide an accurate kinematic description for the species. 5. The degree of acceleration and deceleration during a stroke increased with decreasing body size among species. 6. The power phase lasted for 66–70% of stroke duration, and the ducks accelerated for the first 84% of this phase. During the power phase, work against drag was 10–12%, work against buoyancy was 36–38%, and inertial work in acceleration was 49–54° of the total mechanical work done. 7. Mechanical energy costs of descent, as estimated by the unsteady model, were 47–75% higher than estimates from the steady model. Accelerational stroking had greater effects on descent costs as body size decreased.
Note:
Present address: Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
Gill Movements of Nymphal Ephemera Danica (Ephemeroptera) and the Water Currents Caused by them
Authors: Eastham L. E. S. 
Published: April 2021

ABSTRACT
The nymphs of Ephemera danica living in burrows in the sandy mud of flowing waters present a problem of current production in the water, quite different from those so far investigated (Eastham, 1932, 1934, 1936, 1937)-Percival & Whitehead (1926) collected data indicating that this species is found most commonly in water, flowing over a sandy floor, which contains about 65% coarse sand, 2% fine sand and about 1 % each of silt, fine silt and clay. Their observations also showed that from this type of environment there was little or no migration to neighbouring places where the sand was present in smaller amount and the silt and clay predominated. Experiments showed that the animals always displayed a preference for the soft surface into which burrowing could be effected, but no adequate explanation of the relationship between nymphs and sand was forthcoming. Questions regarding the unsuitability of silt or clay, in any but small quantities, remain unanswered.
Studies on the Growth of Tissues in Vitro
Authors: Trowell O. A. , Willmer E. N. 
Published: April 2021

ABSTRACT
Tissue extracts have been made from several organs of growing and adult fowls, and the growth-promoting properties of these extracts have been tested on periosteal fibroblasts growing in vitro. The growth-promoting properties are most pronounced in brain extract and diminish in the sequence : thyroid, thymus, testis, ovary, bone marrow, liver, kidney and muscle extracts. Extracts made from the spleens of adult cocks were found to be far more efficient growth-promoting agents than extracts made from the spleens of young birds. The growth-promoting power of a tissue extract cannot always be correlated with the age of the tissue from which the extract was made, with the rate of growth of that tissue, nor with its nuclear content.
A Quantitative Study of Amphibian Neural Tube Induction with A Water-Soluble Hydrocarbon
Authors: Shen S. C. 
Published: April 2021

ABSTRACT
The water-soluble carcinogenic hydrocarbon, 1 : 2 : 5 : 6-dibenzanthracene-α-β-endo-succinate, has been implanted in carefully graded doses into gastrulae of Triton alpestris. An optimal dose for neural tube formation was found at 0·0125γ per embryo, and for palisade inductions at 0·000125γ per embryo. It is suggested that the action of this hydrocarbon at least is direct, imitating the action of the naturally occurring organizer substance, and not indirect, by injuring the ventral ectoderm so as to liberate the masked organizer substance which it contains. The effective range of dosage resembles that of many biologically active substances. A parallelism exists between the frequency and the size of the neural tube inductions.
The Motor Mechanism of the Insect Leg
Authors: Pringle J. W. S. 
Published: April 2021

ABSTRACT
A double motor innervation is described from an insect muscle, the two nerve fibres producing respectively a tonic contraction and a twitch. No evidence has been found for the existence of inhibitory fibres. The nature of the two types of contraction is discussed, and compared with the similar double motor innervation of some Crustacean muscles. The distribution of motor fibres to the muscles of the metathoracic leg of Periplaneta is described in detail. The method of utilization of the leg in normal life is discussed.
Antagonism between Salts of the Heavy and Alkaline-Earth Metals in their Toxic Action on the Tadpole of the Toad,Bufo Bufo Bufo(L.)
Authors: Jones J. R. Erichsen 
Published: April 2021

ABSTRACTA brief review is given of the various types of living material and of toxic substances employed by different workers in the study of antagonism. Survival curves are described for the heavy metal salts nickel nitrate, copper nitrate and cadmium nitrate, and the alkaline-earth metal salts magnesium, calcium, strontium and barium nitrate, for the tadpole of the toad, Bufo bufo bufo (L.). A description is given of Osterhout’s method for the detection and measure-ment of antagonism by observing the effect of mixing, in varying proportions, equally toxic solutions of the two substances in question. Survival curves for tadpoles in mixtures of equally toxic solutions of nickel nitrate and strontium nitrate indicate marked antagonistic action between these salts, the effect increasing with dilution. The survival curve for mixtures of the equally toxic solutions 0·03 N copper nitrate and 0·40N strontium nitrate apparently indicate antagonism over a part of the concentration range and synergism over the remainder. This is because a 0·03 N solution of copper nitrate increases in toxicity upon dilution, its toxicity reaching a maximum at approximately 0·0015N. If the normality of the copper solution is below this critical value its mixture with an equally toxic strontium solution gives a normal antagonism curve. It is shown that the other alkaline-earth metals, calcium, magnesium and barium also reduce the toxicity of copper solutions. The strontium concentration— copper concentration—survival time relationship is studied in detail and the way in which the survival time locus is represented by a curved surface is described. The survival surfaces for copper and calcium, copper and magnesium and copper and barium are of similar type. Problems for further investigation arising out of the results are briefly discussed.
Calcium And Calmodulin Antagonists Delay Oral Regeneration In The Ciliate Stentor Coeruleus
Authors: Maloney Michael S. , Walsh Patricia R. , Rhoadarmer Kelly B. 
Published: April 2021

ABSTRACT
The regeneration of a new oral apparatus in Stentor coeruleus (oral regeneration) has been shown to be sensitive to events that inhibit calcium uptake and calmodulin function. Removal of extracellular calcium delays oral regeneration significantly. The calcium channel antagonist verapamil also delays oral regeneration, as does lanthanum, which is known to block calcium uptake. Both inhibitors are active in the concentration range 10−7-10−6 mol l−1. Verapamil acts primarily in the earliest stages of regeneration (prior to stage 5) though some minor delays occur in the later stages as well. In addition, verapamil caused an apparent ‘clumping’ of the pigment granules in the interior of the cell similar to the effects of high concentrations of theophylline and caffeine. The effects of verapamil on oral regeneration were not reversible in the presence of excess extracellular calcium but those of lanthanum were. The calmodulin antagonists trifluoperazine and W-7 were also shown to delay oral regeneration, but the dechlorinated analogue of W-7, W-5, had no effect even at concentrations 10 times those of W-7. The effects of W-7 were not reversed by excess extracellular calcium. These results suggest that calcium uptake is necessary for oral regeneration and that calmodulin is involved in the control and/or formation of the oral apparatus.
The Role of Suction in the Adhesion of Limpets
Authors: Smith Andrew M. 
Published: April 2021

ABSTRACT
Experiments were performed to determine the mechanism by which limpets attach to the substratum. Pressure measurements were made under the feet of three species of limpets as they were forcibly detached from the substratum. These measurements show that limpets actively decrease the pressure under their feet, and in almost every case this pressure decrease can account for all of their tenacity. The results are the same whether the pressure transducer is flush with the surface or connected to the surface via a tube. The tenacity of limpets is dependent on ambient pressure, as predicted for a suction mechanism. Leaks disrupt the attachment of limpets. Thus, for at least an hour after they have been moving, suction appears to be the primary attachment mechanism of limpets. Limpets using suction often have tenacities greater than 0.1 MN m−2, which corresponds to pressures under the foot lower than 0MPa.
If limpets have more than a few hours to attach, approximately 30% of them form a different, stronger attachment that appears to be based on glue. These limpets remain stationary for extended periods. It is hypothesized that limpets in the field alternate between the use of suction and glue, depending on their need for mobility.
Acid-Base Regulation in the Atlantic Hagfish Myxine Glutinosa
Authors: Mcdonald D. G. , Cavdek V. , Calvert L. , Milligan C. L. 
Published: April 2021

ABSTRACT
Blood acid-base status and net transfers of acidic equivalents to the external environment were studied in hagfish, Myxine glutinosa, infused with ammonium sulphate (4mequivkg−1 NFL+) or with sulphuric acid (3mequivkg−1 H+). Hagfish extracellular fluids (ECF) play a greater role in acid-base regulation than in teleosts. This is because hagfish have a much larger blood volume relative to teleosts, despite a relatively low blood buffering capacity. Consequently, infusion of ammonium sulphate produced only half of the acidosis produced in marine teleosts in comparable studies, and hagfish readily tolerated a threefold greater direct H+ load. Furthermore, the H+ load was largely retained and buffered in the extracellular space. Despite smaller acid-base disturbances, rates of net H+ excretion to the external environment were, nonetheless, comparable to those of marine teleosts, and net acid excretion persisted until blood acid-base disturbances were corrected. We conclude that the gills of the hagfish are at least as competent for acid-base regulation as those of marine teleosts. The nature of the H+ excretion mechanism is discussed.
A Novel Type of Ciliary Activity in Stylonychia Mytilus: Analysis of Potential-Coupled Motor Responses in the Transverse Cirri
Authors: Mogami Yoshihiro , Machemer Hans 
Published: April 2021

ABSTRACT
The motor responses of the transverse cirri of Stylonychia mytilus were investigated by applying high-speed microcinematography and step voltageclamp. As a response to hyperpolarization, the transverse cirri began to swing posteriorly from an inactive upright posture at rest. The deeply inclined posture was maintained as long as the hyperpolarizing pulse was on. Upon depolarization, the cirri began to swing towards the anterior end of the cell and continued regular cyclic beating, orienting the effective stroke anteriorly. Motor responses of the transverse cirri occurred in quasi-planar motion, allowing analysis of the bend configuration along the full length of the cirri. Beating activity induced during sustained depolarization was virtually stable, with different oscillation profiles at base and tip. Cyclic movement of the distal region was enhanced at large amplitudes of depolarization. Termination of a hyperpolarizing voltage step induced a transient depolarization-type anterior beating, and termination of a depolarizing step induced a transient posteriad inclination of the transverse cirri. In both hyperpolarization- and depolarization-induced motor responses, a shear angle analysis of the initiation of the response indicated that sliding displacement of doublet microtubules was initiated at the base and propagated towards the tip. The discovery in a ciliary organelle of a very distinct response to hyperpolarizing and depolarizing stimulation is highly useful for the analysis of ciliary electromotor coupling. The functions of intraciliary Ca2+ in the regulation of the motor responses are discussed.