bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sequential Changes in the Adenosinetriphosphatase Activity and the Electrolyte Excretory Capacity of the Nasal Glands of the Duck (Anas Platyrhynchos) during the Period of Adaptation to Hypertonic Saline*
Authors: Fletcher G. L. , Stainer I. M. , Holmes W. N. 
Published: April 2021

ABSTRACT
Regardless of the composition of the incubation medium, the nasal gland tissue from ducks adapted to hypertonic saline always released inorganic phosphate from the ATP in the medium at a higher rate than tissue derived from freshwater-adapted ducks. Changes in the nasal gland ATP-ase activities during the period of adaptation to saline followed the same time course as the changes which occurred in the sodium-excretory capacity of the tissue. Adaptation to saline resulted in a three-to fourfold increase in the weight-specific ATP-ase activity which was accompanied by a three-to fourfold increase in the weight-specific sodium-excretory capacity. In the saline-adapted birds a positive correlation was found between the sodium-excretory capacity of the nasal gland tissue and the corresponding ATP-ase activity. The moles of sodium excreted per mole of ATP hydrolysed was constant irrespective of whether the birds were adapted to either fresh water or salt water. Concommitant with the changes in weight-specific sodium excretion and ATP-ase activity, an increase in the sodium concentration of the nasal gland fluid was observed. An approximately twofold increase in nasal gland weight also occurred during this period. All changes which were observed to occur during the period of adaptation to saline were reversed when the birds were returned to fresh water. The observed changes in enzyme activity and sodium excretory rates of the nasal glands are discussed in relation to possible cellular changes which might occur and their importance relative to the birds’s ability to adapt to a marine environment.
Metachronal Co-ordination of the Comb Plates of the Ctenophore Pleurobrachia
Authors: Sleigh M. A. 
Published: April 2021

ABSTRACT
The activity of comb plates of Pleurobrachia was analysed from cine films. The interval between successive beats of a comb plate varied from several seconds to about 50 msec, in normal sea water; this variation in frequency was accompanied by a variation wave velocity. There was an almost linear relationship between wave velocity and frequency, ranging from a minimal wave velocity of about 20 mm./sec. at low frequencies to a maximal wave velocity of about 80 mm./sec. at the highest frequencies. The wave velocity was accelerated at low frequencies by increased Mg2+ concentrations, by ouabain and by curare, and the same substances decreased the wave velocity at high frequencies. The frequency of beat was accelerated by certain concentrations of adrenaline, serotonin, Mg2+, ouabain and curare. Decreases of frequency were found in acetylcholine (and eserine) and strychnine. These substances act on the excitability of the pacemaker. It is concluded that metachronal transmission is by a flow of electric current from one comb plate to the next. Depolarization, either by a recent excitation of the comb plate or by agents like ouabain causes increased excitability and a more rapid transmission. The minimum phase difference between adjacent comb plates was about 5 msec. The comb plates are almost entirely dependent on a conducted impulse for their excitation; occasionally a spontaneous excitation occurs. The membranelles of Stentor depend more on excitation within the ciliary base and less on the conducted impulse. The two systems are believed to share common features, but differ in the relative importance of these features. Reverse waves involving the beating of comb plates in the normal direction were observed. The wave velocity of these waves increased only slightly over a wide frequency range. Reverse waves of this type are believed to be transmitted by mechanical contact between the comb plates.
Active Transport by the Cecropia Midgut
Authors: Nedergaard S. , Harvey W. R. 
Published: April 2021

ABSTRACT
Although the addition of 32 mM/l. choline chloride to the standard bathing solutions depresses the short-circuit current of the isolated midgut, the replacement of the added choline chloride by either sodium or lithium chloride has no further affect on the current. No net flux of either sodium or lithium is measureable by atomic absorption spectrometry. Therefore neither sodium nor lithium is actively transported across the midgut. Rubidium is able to substitute fully for potassium in maintaining a short-circuit current. The net fluxes of rubidium and potassium are approximately in the same ratio as their concentrations in the solutions bathing the blood-side of the isolated midgut. Therefore the midgut is unable to distinguish between potassium and rubidium. Ammonium is unable to replace potassium in sustaining a current. In double-label experiments using 42K to measure one unidirectional flux and 86Rb to measure the other, the net potassium-rubidium flux accounts for about 87 % of the short-circuit current. The short-circuit current increases with increasing potassium concentration, at least in the range from 2 to 64 mM/l., although the exact function depends on the conditions under which the measurements are made. The midgut isolated from the Cecropia silkworm appears to possess a ‘potassium pump’ with the simple ionic requirement that potassium be present in the solution bathing the blood-side and presumably that potassium be present in the cells.
Ionic Regulation of the Baltic and Fresh-Water Races of the Isopod Mesidotea (Saduria) entomon (L.)
Authors: Croghan P. C. , Lockwood A. P. M. 
Published: April 2021

ABSTRACT
The isopod Mesidotea entomon has colonized the Baltic and certain Swedish lakes since the end of the last Ice Age. The ionic regulation of Baltic animals and fresh-water animals (L. Mälaren) has been compared. It has been possible to adapt Baltic animals to very dilute media, but 5 % Askö sea water (5·5 mM/l. Na) appears to be the limit of adaptation. The haemolymph sodium concentration of Baltic animals from the very dilute media was considerably lowered. The haemolymph sodium concentration in Mälaren animals is high (250 mM/l. Na) and comparable with that in Baltic animals in much more concentrated solution. The haemolymph ionic ratios of the Baltic and freshwater animals are similar. The Cl : Na ratio rises slightly in the more concentrated haemolymph samples. From the concentration of ions in the haemolymph and in the total body water, the relative volume of the haemolymph was calculated. Mälaren animals appear to have a much larger haemolymph volume. The permeability of the animals was determined from the rate of loss of sodium into de-ionized water. The permeability of the Mälaren animals is considerably reduced compared to the Baltic animals. Permeability is not related to the medium to which the animals had been adapted. The sodium influx was determined using 22Na. The rate of active uptake was calculated from this. The maximal rate of active uptake was similar in Baltic and Mälaren animals. The sodium concentration of the medium at which active uptake was half maximum (KM) was considerably lower in Mälaren animals than in Baltic animals. The evolution of Mesidotea as a fresh-water animal is interpreted as a result of a reduction in permeability of the external surfaces to NaCl and an increase in the affinity of the active transport mechanism enabling the animal to maintain the haemolymph NaCl concentration in a steady state in fresh water.
Active Transport by the Cecropia Midgut
Authors: Haskell J. A. , Harvey W. R. , Clark R. M. 
Published: April 2021

ABSTRACT
The electrical potential across the isolated midgut of five developmental stages of the Cecropia silkworm was studied by changing the concentration of single cations in solutions bathing each side of the midgut. The stages included feeding fourth-instar insects, insects moulting from the fourth to the fifth instar, feeding fifth-instar insects, insects which had evacuated their midguts, and insects spinning cocoons. Average values of the initial maximal potential exhibited by the midgut in solutions containing K, Mg, and Ca but no Na, for the stages mentioned above, were 68, 83, 90, 124, and 2 mV., respectively. In all of the developmental stages studied except the ‘spinning larva’, reducing the potassium concentration from 32 to 2 mM/l. on the blood-side of the isolated gut lowers the potential, on the lumen-side of the gut raises the potential and on both sides gives an intermediate value. When the potential prior to a decrease in concentration of potassium on the blood-side is over 100 mV., the Nernst slope approaches 59 mV. A tenfold reduction in the concentration of magnesium or the addition of 32 mM/l. sodium to the solutions bathing the isolated gut has no systematic effect on the potential. A tenfold drop in the concentration of calcium in the solutions causes changes in the potential in the opposite direction from those predicted by the Nernst equation. The pH of the midgut contents rises from early fourth instar to late fifth instar. The hydrogen-ion concentration of the blood is about 1000 times more than that of midgut contents in fifth-instar insects. Neither synthetic ecdysone, partially purified natural ecdysone nor juvenile hormone has an effect on the potential or current of the isolated midgut over periods as long as 30 min.
Visual Thresholds and Spectral Sensitivity of Herring Larvae
Authors: Blaxter J. H. S. 
Published: April 2021

ABSTRACT
Herring larvae are characterized by eyes with no rods and no retinomotor responses, though both are present in the adult. By observing the extinction of phototactic behaviour and feeding in herring larvae of different ages held at low intensities of white and coloured light, it was possible to obtain a measure of both threshold light intensities and spectral sensitivity for a pure-cone eye. The phototaxis was positive at higher intensities, the threshold being 100 to 10−1 m.c. Below this threshold a negative phototaxis was observed which disappeared at a much lower threshold, about 10−5 to 10−6 m.c. The threshold for feeding varied with age and the type of food organism, lying between 10−1 and 10−2 m.c. The high sensitivity for negative phototaxis was probably a visual response and not one mediated by a dermal light sense. Spectral sensitivity varied depending on age and behavioural criteria. Using feeding and positive phototaxis the action spectrum was broad and plateau-like with a maximum in the yellow-green and would appear to be similar to other photopic curves. The action spectra for negative phototaxis showed a number of peaks. At hatching three peaks at 450, 520 and 600 mμ might represent three types of cone as postulated by the Young-Helmholtz theory of colour vision.
Respiratory Exchange and Evaporative Water Loss in the Flying Budgerigar
Authors: Tucker Vance A. 
Published: April 2021

ABSTRACTOxygen consumption of 2 budgerigars (Melopsittacus undulatus) was measured during level, ascending and descending flights lasting 5–20 min. in a wind-tunnel at speeds between 19 and 48 km./hr. In level flight oxygen consumption was lowest at 35 km./hr. with a mean value of 21·9 ml. (g. hr.)−1 or 12·8 times the standard value calculated for these birds (weight = 35 g.). At a given speed oxygen consumption was highest for ascending flight and lowest for descending flight. Carbon dioxide production was measured on one bird flying level at 35 km./hr. for 20 min. The ratio of carbon dioxide production to oxygen consumption was 0·780, indicating that the bird was oxidizing primarily fat. The efficiencies of level, ascending and descending flight are discussed. The measurements indicate that for the budgerigar 42 km./hr. is the most economical speed for covering distance, and below 27 km./hr. undulating flight is more economical than flight at a constant altitude. Evaporative water loss in level flight was measured in two birds for 20 min. at 35 km./hr. at temperatures of 18–20° and 29–31° C. At 36–37° C. the birds became overheated and would not fly for as long as 20 min. Evaporative water loss at 18–20° C. was 20·4 mg. (g. hr.)−1. It increased to 63·9 mg. (g. hr.)−1 at 36–37° C. After accounting for metabolic water production and faecal water loss, budgerigars flying at 18–20° C. had a net water loss of 11 mg. (g. hr.)−1. At this temperature 15 % of the estimated heat production in flight was lost by evaporation of water, while 47% was lost by evaporation of water at 36–37° C. Lung ventilation, tidal volume and partial pressure of carbon dioxide in expired air were estimated for flying budgerigars from evaporative water-loss data. In level flight at 18–20° C and 35 km./hr. these quantities had values of 398 ml. (g. hr.)−1, 0·033 ml. (g. breath)−1 and 37 mm. Hg. respectively. Respiratory rate in level flight was measured in 2 birds at speeds between 19 and 48 km./hr. Respiratory rate depended on speed and was lowest at 35 km./hr. Since wing-beat frequency was constant at 840 beats/min. at all speeds, respiratory rate and wing-beat frequency were not synchronized. Published data and analysis of dimensional relations of birds suggest that in birds the size of a budgerigar or smaller a respiratory rate equal to the wing-beat frequency would be too high for efficient ventilation of the lungs. Birds the size of a pigeon or larger probably have synchronous wing beats and respirations.
Structure and Physiology of A Chordotonal Organ in the Locust Leg
Authors: Usherwood P. N. R. , Runion H. I. , Campbell J. I. 
Published: April 2021

ABSTRACT
The structural and physiological properties of a chordotonal organ found in the metathoracic femoral segments of the locust and grasshopper are described. Recordings from the afferent fibres of this mechanoreceptor reveal two patterns of activity: a static or tonic discharge and a dynamic or phasic, rapidly adapting discharge. The frequency of the tonic discharge varies with the femur-tibia angle, while the phasic discharge occurs in response to angular movements of the tibia of &gt; 3’. The frequency of the phasic response is related to the velocity of tibial displacement. The responses recorded during flexion of the tibia are different from those recorded during extension. Removal of either of the metathoracic chordotonal organs produces significant changes in walking and postural behaviour. Leg reflexes involving the femoral chordotonal organ and femoral muscles appear to play a very significant role during postural and walking activity.
Sodium Regulation and Adaptation to Fresh Water in Gammarid Crustaceans
Authors: Sutcliffe D. W. 
Published: April 2021

ABSTRACTSodium uptake and loss rates are given for three gammarids acclimatized to media ranging from fresh water to undiluted sea water. In Gammarus zaddachi and G. tigrinus the sodium transporting system at the body surface is half-saturated at an external concentration of about 1 mM/l. and fully saturated at about 10 mM/l. sodium. In Marinogammarus finmarchicus the respective concentrations are six to ten times higher. M. finmarchicus is more permeable to water and salts than G. zaddachi and G. tigrinus. Estimated urine flow rates were equivalent to 6·5 % body weight/hr./ osmole gradient at 10° C. in M. finmarchicus and 2·8 % body weight/hr./osmole gradient in G. zaddachi. The permeability of the body surface to outward diffusion of sodium was four times higher in M. finmarchicus, but sodium losses across the body surface represent at least 50 % of the total losses in both M. finmarchicus and G. zaddachi. Calculations suggest that G. zaddachi produces urine slightly hypotonic to the blood when acclimatized to the range 20 % down to 2 % sea water. In fresh water the urine sodium concentration is reduced to a very low level. The process of adaptation to fresh water in gammarid crustaceans is illustrated with reference to a series of species from marine, brackish and freshwater habitats.
Effects of Sub-Lethal High Temperature on An Insect, Rhodnius prolixus (Stål.)
Authors: Okasha A. Y. K. 
Published: April 2021

ABSTRACT
The effect on moulting of exposing 1st-, 2nd-, 3rd- and 4th-stage larvae of Rhodnius to 36.5° C. immediately after feeding was studied. After transfer to normal temperature (28° C.) moulting is delayed; the duration of the delay is directly proportional to the period of exposure to high temperature. Unfed larvae exposed to high temperature exhibit delayed moulting when placed at normal temperature after feeding, and prolonged exposure also inhibits micturition which normally occurs directly after feeding. Since the Malpighian tubules appear to function normally, it is suggested that the inhibition of the mechanisms responsible for emptying the rectum results in the cessation of micturition. The harmful effects on moulting of heat-treatment of unfed larvae can be eliminated by placing the exposed insects at normal temperature for an appropriate period before feeding. Exposure to high temperature either before or after feeding results in the decrease and malformation of the sensory bristles and plaques in the next larval stage.
Molecular Sieving of Hydrophilic Molecules by the Rectal Intima of the Desert Locust (Schistocerca gregaria)*
Authors: Phillips J. E. , Dockrill A. A. 
Published: April 2021

ABSTRACT
The permeability of perfused intimal sacs to fourteen non-ionic, hydrophilic molecules of graded molecular size was estimated by radioisotope flux. The rectal cuticle acts as a molecular sieve severely restricting the rate of penetration of molecules with increasing hydrated size. The penetration of test molecules was as predicted by the Renkin equation for a uniform population of water-filled pores having radii of 6.5 Å. The properties of cuticles from the rectum and the integument are compared and the role of the rectal intima in the excretory process in the desert locust is discussed.
Recurrent Inhibition in the Giant-Fibre System of the Crayfish and its Effect on the Excitability of the Escape Response
Authors: Roberts Alan 
Published: April 2021

ABSTRACTA single impulse in any one of the central giant fibres of the crayfish is sufficient to evoke a full escape response. Following such a single impulse a search was made for inhibitory processes of similar duration to the driving movement of the escape response. There is no inhibition of flexor motoneurones or muscles to prevent response to impulses in the central giant axons during the escape response. However, following an impulse in any central giant, intracellular recording showed that there is inhibition of excitatory input to the lateral giants in the abdomen. This inhibition suppresses impulse generation for the duration of the escape response. The inhibition coincides with slow, depolarizing potentials in the lateral giants. These have an equilibrium potential between the normal resting potential and the threshold for spike initiation in the lateral giants. During these slow potentials there is a postsynaptic resistance decrease coinciding very closely in time course with the inhibition of excitatory input. The slow potentials are therefore identified as IPSPs (inhibitory postsynaptic potentials) because of their close association with a postsynaptic inhibitory process. This conclusion is endorsed : (a) by the absence of similar slow potentials in the abdominal medial giants which have no excitatory input at this location, and (b) by the diminution of the slow potentials by picrotoxin, a drug known to block inhibition at many crustacean synapses. When evoked repetitively, even at low frequencies like 0·25 per sec., the IPSPs decrease in amplitude. No other ‘after effects’ of repeated activity were found. Attempts to localize the inhibitory synapses are frustrated by the large space constant of the lateral giants. However, the evidence is compatible with the notion that inhibition originates within each abdominal ganglion. There is occlusion and crossed response decrement between the central giant axons evoking lateral giant inhibition. This suggests that the different presynaptic fibres excite some common inhibitory pathway in each ganglion. Further experiments showed that pathways producing inhibition in one ganglion can be excited in others. Interneuronal arrangements to explain properties of the inhibitory pathways are discussed. Two functions are suggested for the recurrent inhibition in the crayfish lateral giants. First, it may limit the number of impulses that are evoked by a single afferent excitatory volley. Secondly, it may coordinate successive escape responses by suppressing impulse generation in the lateral giants during such responses.
Aestivation and Ionic Regulation in Two Species of Pomacea (Gastropoda, Prosobranchia)*
Authors: Little Colin 
Published: April 2021

ABSTRACT
The ionic composition of the haemolymph, and the concentrations of uric acid and protein, have been determined for the amphibious prosobranchs Pomacea lineata and P. depressa. Ionic composition of the haemolymph is similar to that of freshwater gastropods. The urine is decidedly hypo-osmotic to the haemolymph, reabsorption of ions occurring in the anterior chamber of the kidney. The rate of production of urine is approximately 1 μl./g./min. at 25° C. The onset of aestivation appears to be related to a loss of 20 % of the normal wet weight of the tissues. The loss of weight during aestivation averages 0·009 % of initial wet weight/hr., and aestivation may continue for over 400 days. During aestivation the osmotic pressure of the haemolymph may rise to twice its normal value; but this is 30 mM/l. NaCl less than that predicted from weight losses. The relative composition of the haemolymph alters little, except that the percentages of sodium and chloride increase. Uric acid accumulates round the blood vessels during aestivation, especially in the lung. Relatively little accumulates in the two chambers of the kidney, and only that in the posterior chamber is excreted later. Since the volume of fluid in the posterior chamber falls to about 10 % of its normal value, while the total loss of weight of the snail is about 50 %, the fluid in the posterior chamber acts as a water reserve. Recovery from aestivation occurs in about 24 hr., when the snails are placed in water. The posterior chamber of the kidney excretes high concentrations of uric acid during this time. The characteristics of aestivation are discussed, and compared with those shown by the Pulmonata.