Showing papers in "The Journal of Experimental Biology in 1958"

The Speed of Swimming of Fish as Related to Size and to the Frequency and Amplitude of the Tail Beat

Abstract: 1. An apparatus is described in which it is possible to study and record the continuous swimming of fish at speeds up to 20 m.p.h. 2. Records made of the swimming at different speeds of dace, trout and goldfish measuring up to 30 cm. in length are reproduced. 3. Speed at any particular frequency of tail beat is shown to be directly related to the length of the specimen, measured from the tip of the snout to the most posterior extremity of the tail. 4. Above a frequency of 5 tail beats per second speed is directly dependent upon frequency up to the maximum values recorded. The results for all sizes and species recorded may be adequately expressed by the formula V = ¼{ L (3 f - 4)}, where V is the speed in cm. per sec., f is the frequency in beats per sec. and L is the body length in cm. 5. The distance travelled per beat (and hence the speed) is directly dependent upon the amplitude of the tail beat. 6. The amplitude increases with increasing frequency up to a maximum reached at about beats per second. This maximum amplitude is the same for all fish tested and is about one-fifth of the body length. 7. The maximum frequency attainable decreases with increasing size of the specimen. This decrease is slight in the trout and more pronounced in the dace and goldfish. Estimation of the possible maximum frequencies of much bigger fish allows for prediction of the maximum speeds they may be able to attain. Such predicted speeds are in accord with the few measurements that have been made and are of the order of 10 body lengths per second up to a size of 1 m.

On the Function and Evolution of Electric Organs in Fish

Abstract: 1. The electric discharges of Gymnarchus niloticus and of representative species of seven genera of the Mormyridae have been examined in their natural habitat in Africa and in the laboratory. 2. Comparable investigations of the South American Gymnotidae have shown the existence of two discharge types in both these unrelated fish families. 3. The first type of electric discharge consists of very regular sequences of continuously emitted, monophasic pulses, varying from species to species in frequency, and within narrower limits from individual to individual. 4. Fish emitting this first type of pulses include Gymnarchus , Hypopomus and Eigenmannia . The frequency range for these fish lies between 60 and 400 discharges/sec. 5. The frequency does not alter with the state of excitation of the fish. The duration of individual pulses is relatively long, i.e. 2-10 msec. 6. The second type of discharge is less regular in frequency, the pulse duration much shorter and the pulse shape more complex. The individual discharge from the whole electric organ lasts about 0.2 msec, in Petrocephalus . 7. This type of discharge is found in all the examined species of the Mormyridae and in such forms as Gymnotus carapo and Staetogenes elegans . 8. The basic discharge rate of a resting mormyrid is somewhat variable and not strictly rhythmical. It usually lies between 1 and 6 pulses/sec. 9. Stimuli which excite the mormyrids cause an increase in the discharge frequency. The recorded maximum is about 130 pulses/sec. 10. Suitable stimuli can inhibit the discharges of the Mormyridae for prolonged periods. 11. In Gymnotus carapo and Staetogenes elegans the basic discharge rate is higher and of regular rhythmicity. Depending on temperature the frequencies lie between 30 and 87 pulses/sec. When these fish are excited the frequencies are increased up to 200 pulses/sec, for a short time. 12. The shape of the electric field, which is set up with each pulse around the fish, has been examined. 13. A theory has been proposed which suggests that these fish, by means of their electric pulses, can locate objects if their electrical conductivity differs from that of water. 14. These fish have shown themselves extremely sensitive to influences affecting the electric field. This has been studied by applying artificial electric stimuli, by studying the effects of conductors and non-conductors introduced into the field, and the reactions towards magnetic fields and electrostatic charges. 15. Conditioned reflex experiments with Gymnarchus niloticus and Gymnotus carapo have shown that these fish can detect the presence of a stationary magnet, and that they can discriminate between conductors and non-conductors. 16. The prey of these fish does not appear to be affected by the discharges. Inter alia , the electric pulses have a social significance. 17. This locating mechanism may be considered as an adaptation to life in turbid water. 18. Gymnotidae and Mormyridae (taken to include Gymnarchus ) show striking features of convergent evolution. 19. Unusual locomotory adaptations such as swimming by means of the dorsal fin ( Gymnarchus ), the anal fin (Gymnotidae) and ‘Gemminger9s bones’ (Mormyridae) may be considered as a means which tends to make the axis of symmetry of the fish and of its electric field coincide during active movements. 20. A new theory for the evolution of electric organs has been suggested. A major prerequisite appears to be a receptor sensitive to electrical stimulation. 21. It is suggested that special sensory and nervous differentiations of the lateralis system (‘mormyromasts’, valvulae cerebelli) are concerned with the perception and integration of electric stimuli. 22. Muscular action potentials have been recorded in the water at some distance from non-electric fish. 23. The easiest explanation for the evolution of strong electric organs would appear to start from such muscular action potentials, and proceed via weak electric organs used for orientation, to the powerful offensive and defensive electric organs.

The Mechanism of Object Location in Gymnarchus Niloticus and Similar Fish

Abstract: 1. Experiments with moving electrostatic and magnetic fields show that Gymnarchus niloticus is sensitive to a potential gradient of about 0.03 µ V./cm. 2. Alternative explanations of some previous experiments are given in terms of this high d.c. sensitivity. 3. An explanation in similar terms is given of experiments in which Gymnotus carapo is trained to detect a stationary magnet. 4. The mechanisms available for the location of objects by electric fish are reviewed. It is concluded from the results of a critical experiment (described in a succeeding section) that Gymnarchus niloticus can detect objects by the disturbance of its own electric field in the water. 5. The approximate theory of this method of object location is derived. The effect on the receptors of the perturbing field due to an object depends on the electrical properties of the receptors: in the extreme cases the stimulation of the receptors is proportional either to the potential or to its second derivative. Graphs are given showing the effect of an object on the potential and on its second derivative around the surface of the fish. 6. Experiments are described using Gymnarchus niloticus which ( a ) confirm that the mechanism of object location employs electric field distortion; ( b ) indicate the limits of the sensitivity of the fish. 7. The second derivative mode appears to be the most probable one operating in Gymnarchus . The experimentally determined limits of detection are discussed in relation to the random noise in the receptor circuit: it is concluded that both spatial and temporal integration are likely to be employed. 8. The thresholds for object location and for response to direct currents are compared: it is concluded that the same receptors are probably operating in both cases.

Studies on the Feeding and Nutrition of Tuberolachnus Salignus (Gmelin) (Homoptera, Aphididae)

Abstract: 1. The aim of this investigation has been to determine the sugar and nitrogen composition of the phloem sieve-tube sap ingested by Tuberolachnus salignus (Gmelin) feeding on Salix acutifolia stems, and to compare it with that of the honeydew excreted by the aphids. 2. A cage suitable for confining T. salignus on the willow stems is described. 3. Details are given of a technique, outlined by Kennedy & Mittler (1953) for collecting the fluid, termed stylet-sap, which exudes from the cut end of severed embedded stylet-bundles. 4. A method is described for collecting honeydew droplets immediately they are excreted by feeding T. salignus . 5. The nitrogenous matter ingested by T. salignus is in the form of free amino-acids and amides. The same amino-acids and amides are ingested but in greater amounts than they are excreted. 6. The number and concentration of the amino-acids and amides in stylet-sap and honeydew fluctuate with the seasonal development of the host plant. 7. The honeydew contains sucrose, fructose, glucose and melezitose. These sugars are derived from sucrose, the only sugar normally ingested. 8. The evidence for the identity of stylet-sap with the unchanged sieve-tube sap of the host plant is discussed.

Wave Propagation along Flagella

Abstract: 1. The types of bending waves which can propagate along a thin elastic filament immersed in a viscous medium are derived. 2. It is not possible to account for the form of the waves observed on actual flagella if the flagellum is regarded merely as a passive elastic filament driven from its proximal end. 3. The observed wave forms can be explained by assuming active contractile elements distributed along the length of the flagellum. These elements could be activated by local bending.

The Effects of Temperature and of Egg-Laying on the Longevity of Drosophila Subobscura

Abstract: 1. The adult life span of Drosophila subobscura has been measured at temperatures varying from 20° to 33° C. A sharp increase in the slope of the curve of log survival time against temperature occurs at temperatures above 31° C. 2. Changes which occur in individuals at 33° C. or above are reversible, at least in part, at 20° C.; but changes occurring at 30·5° C. are irreversible in the sense that the total survival time at 30·5° C. is not increased by intervening periods at 20° C. 3. Exposure of young adult flies to 30·5° C. for a period of about half their expectation of life at that temperature significantly increases the further expectation of life of females at 20° C. but does not alter the expectation of life of males. Such exposure causes a partial regression of the ovaries of females, a permanent change in their behaviour and a reduction in their rate of egg-laying; exposure does not alter the behaviour or seriously reduce the fertility of males. 4. ‘Ovariless’ females and virgin females live for significantly longer than do normal mated females. The expectation of life of ‘ovariless’ females at 20° C. is not altered by exposure to 30·5° C. It is concluded that egg-laying accelerates the ageing of females at 20° C., and that the prolongation of life of females exposed to 30·5° C. is due to the reduction in the rate at which such females subsequently lay eggs.

Tidal and Diurnal Rhythms of Locomotory Activity in Carcinus Maenas (L.)

Abstract: 1. Spontaneous locomotory activity was recorded continuously for several days in Carcinus maenas (L.). 2. A complex rhythm was observed which could be analysed into two components, one of diurnal frequency (24 hr.), with peaks of activity during the hours of darkness, and one of tidal frequency ( ca . 12.4hr.), with peaks at the time of high tide. 3. The rhythms persist in constant dim light at constant temperatures, whether the crabs are kept moist in air or continuously immersed in sea water. 4. The resultant effect of the two rhythms is to produce particularly high activity peaks during periods which recur with a semi-lunar frequency. 5. Experimental results relate to observed behaviour on the shore.

Studies on the Feeding and Nutrition of Tuberolachnus Salignus (Gmelin) (Homoptera, Aphididae) : II. The Nitrogen and Sugar Composition of Ingested Phloem Sap and Excreted Honeydew

Abstract: 1. The aim of this investigation has been to determine the sugar and nitrogen composition of the phloem sieve-tube sap ingested by Tuberolachnus salignus (Gmelin) feeding on Salix acutifolia stems, and to compare it with that of the honeydew excreted by the aphids. 2. A cage suitable for confining T. salignus on the willow stems is described. 3. Details are given of a technique, outlined by Kennedy & Mittler (1953) for collecting the fluid, termed stylet-sap, which exudes from the cut end of severed embedded stylet-bundles. 4. A method is described for collecting honeydew droplets immediately they are excreted by feeding T. salignus. 5. The nitrogenous matter ingested by T. salignus is in the form of free amino-acids and amides. The same amino-acids and amides are ingested but in greater amounts than they are excreted. 6. The number and concentration of the amino-acids and amides in stylet-sap and honeydew fluctuate with the seasonal development of the host plant. 7. The honeydew contains sucrose, fructose, glucose and melezitose. These sugars are derived from sucrose, the only sugar normally ingested. 8. The evidence for the identity of stylet-sap with the unchanged sieve-tube sap of the host plant is discussed.

The Co-Ordination of Insect Movements: III. Swimming in Dytiscus, Hydrophilus and a Dragonfly Nymph

Abstract: 1. Movements of the legs during the swimming of adult Dytiscus marginalis and Hydropphilus piceus have been analysed from films. In both beetles the middle and hind pairs of legs play an active part and the front pair is held stationary beneath the thorax. 2. The two legs of a segment are retracted simultaneously in Dytiscus , the two limb pairs acting alternately. In Hydrophilus retraction of a hindleg is simultaneous with that of the contralateral middle leg. Movement is rectilinear in both insects, but the head of Hydrophilus rotates a little to the side opposite that on which the hindleg is retracting. 3. Following amputation of a single hindleg, Dytiscus swims along a relatively straight path as a result of modifications in the movements of the two middle legs and the remaining hindleg. Contrary to the description of Bethe & Woitas, the hindleg continues to alternate with the contralateral middle leg, the only change in rhythm being a delay in the retraction of the other middle leg. Some of the changes in action of these legs are similar to those used in turning of the normal insect and those which produce circling in unilaterally blinded insects. 4. Forced rotation of Dytiscus elicits compensatory movements which tend to produce circling in the opposite direction. The eyes, antennae and legs are the sites of receptors whose asymmetric stimulation produces this response. It is suggested that a similar asymmetry in the inflow from these sense organs is responsible for the modified movements following limb amputations. 5. In the swimming of nymphs of Anax the legs retract slightly before shortening of the abdomen takes place. Although all the segments take part, a large proportion of this shortening occurs in segments 6-8 which contain the branchial chamber. Water is ejected through a small aperture during this contraction but when water is drawn in the anal valves are open wide. 6. The pressure in the branchial chamber rises to about 30 cm. water within 0.03 sec. and the reaction from the jet enables the animal to attain speeds of 30-50 cm./sec. within the first centimetre of propulsion. The duration of this pressure and of the impulse on the animal correspond with the time during which the abdomen contracts longitudinally.

The Osmotic and Ionic Regulation of Artemia Salina (L.)

Abstract: 1. It has been possible to adapt Artemia to sea-water media varying from 0.26% NaCl to crystallizing brine. In fresh water or distilled water survival is relatively short. 2. The osmotic pressure of the haemolymph is relatively independent of the medium and increases only slightly as the medium is made more concentrated. In the more concentrated media the haemolymph is very markedly hypotonic. In media more dilute than 25% sea water the haemolymph is hypertonic. In distilled water there is a rapid fall of haemolymph concentration. The haemolymph of nauplii from sea water is hypotonic. 3. The sodium, potassium, magnesium, and chloride concentrations of the haemolymph have been determined. The bulk of the haemolymph osmotic pressure is accounted for by sodium and chloride ions. The ionic ratios of the haemolymph are relatively constant, and very different from those of the medium. 4. The concentrations of ions in the whole animal have been studied. The chloride space is extremely high. Such changes in haemolymph osmotic pressure that do occur as the medium concentration is varied are due more to net movements of NaCl into or out of the body than to water movements. 5. Evidence is collected to show that an appreciable degree of permeability exists. Most of this permeability is localized to the gut epithelium, the external surface being much less permeable. 6. It is clear that Artemia must possess mechanisms that can actively excrete NaCl and take up water in hypertonic media. It has been demonstrated that Anemia can lower the haemolymph osmotic pressure by excreting NaCl from the haemolymph against the concentration gradient.

The absorption of glucose from the alimentary canal of the locust Schistocerca gregaria (Forsk.).

Abstract: 1. The absorption of glucose from the alimentary canal of Schistocerca gregaria has been studied by filling the gut with a saline solution containing 14 C-labelled glucose together with a dye, Amaranth, which was used as a marker. The net percentage absorption was calculated from the glucose/dye ratio in the various parts of the alimentary canal. 2. The bulk of the glucose was absorbed from the mid-gut caeca, smaller amounts being absorbed by the ventriculus. 3. Glucose absorption was studied at concentrations of 0.002, 0.02 and 0.20M/l. in solutions in which the total osmolarity was maintained by altering the NaCl concentration. The percentage absorption was similar at concentrations of 0.002 and 0.02M/l., but was significantly less at 0.20M/l. 4. The fate of the 14 C-labelled glucose was followed using paper chromatography. The glucose was shown to be rapidly converted to trehalose in the haemolymph. At a concentration of 0.20M/l. this mechanism became saturated and excess glucose accumulated in the haemolymph. 5. The absorption of glucose in vitro , from a gut suspended in a relatively large volume of poisoned saline, was found to be similar to that in the intact insect. 6. From these observations it is suggested that glucose is absorbed by diffusion across the gut wall and that the process is facilitated by the rapid conversion of glucose to trehalose in the haemolymph, which tends to maintain a steep concentration gradient across the gut wall.

Excretion by the Malpighian Tubules of the Stick Insect, Dixippus Morosus (Orthoptera, Phasmidae): Amino Acids, Sugars and Urea

Abstract: 1. Contrary to expectation, it is found that metabolically useful substances pass into the urine and are reabsorbed in the rectum. 2. The kinetics of penetration have been investigated for six amino acids, three sugars and urea. 3. The evidence indicates that these substances enter the urine by passive diffusion. 4. The role of the Malpighian tubules in the insect9s excretory system is discussed in the light of these findings. It is suggested that the tubule is primarily a means whereby all soluble substances of low molecular weight are removed from the haemolymph and that in this respect it has analogies with the glomerulus as well as with the tubule of the vertebrate nephron.

The Inorganic and Amino Acid Composition of Some Lamellibranch Muscles

Abstract: 1. Measurements have been made of the inorganic ion and free amino acid content of a number of lamellibranch muscles. The volumes of extracellular fluid in the muscles have also been determined so that the intracellular concentrations can be calculated. 2. The fast portion of the adductor muscle of Pecten contains about 160 mM. K/kg. fibre water and only 43 mM. Na/kg. fibre water and 34 mM. Cl/kg. fibre water. The potassium and chloride are approximately in a Donnan equilibrium with the potassium and chloride in the blood. 3. In the slow portion of the adductor muscle of Pecten and in the two parts of the adductor and in the byssus retractor of Mytilus , the concentrations of potassium in the fibres are from 150 to 160 mM./kg fibre water, of sodium 73 to 95 mM./kg. fibre water and chloride 94 to 152 mM./kg. fibre water. The potassium and chloride in the fibres are not in a Donnan equilibrium with the potassium and chloride in the blood. 4. The fast and slow fibres of the adductor muscles of Anodonta contain 21 and 17 mM./kg. fibre water of potassium respectively, 5·3 and 7·2 mM./kg. fibre water of sodium, and 2·4 and 5·4 mM./kg. fibre water of chloride. The potassium and chloride in the fibres is not in a Donnan equilibrium with the potassium and chloride in the blood. 5. The fast fibres of Mytilus adductor contain 295 mM./kg. fibre water of free amino acids and 39 mM./kg. fibre water of acid-soluble phosphate compounds. The fast fibres of Anodonta adductor contain only 11 mM./kg. fibre water of amino acids and 19·8 mM./kg. fibre water of phosphate compounds. 6. Mytilus muscles fibres adapt to a reduced blood concentration, partly by an increase in water content and partly by a reduction in the sodium, chloride and free amino acid content. 7. Anodonta muscle fibres adapt to an increased blood concentration, partly by a reduction in the water content and partly by an increased sodium and chloride content. 8. The significance of these results is discussed. It is concluded that the ionic contents of the lamellibranch smooth muscles are consistent with equilibria systems in which the permeability to sodium is significant compared with the permeability to potassium and in which both a sodium and a potassium pump operate.

Factors Controlling the Change of Shape of Certain Nemertean and Turbellarian Worms

Abstract: 1. Nemerteans and turbellarians have an inextensible fibre system around them in the form of a lattice of left- and right-handed spirals. The effect of this system on the change of shape on these worms has been analysed theoretically and compared with the observed behaviour of nine species of turbellarian and nemertean from widely differing habitats. 2. The following theoretical relationships have been studied: ( a ) Variation of the angle between the geodesics and the longitudinal axis of the worm during changes in length, and the role of the fibre system in limiting changes in length of the animal. ( b ) The change in cross-sectional shape during changes in length. ( c ) The extension of the fibres and the extensibility of the worms, assuming the fibres of the lattice to be elastic. 3. The species investigated conform with the theoretical predictions to varying degrees and have been grouped accordingly: ( a ) Geonemertes dendyi and Rhynchodemus bilineatus have low extensibilities and fit the prediction well. They are nearly circular in cross-section at all lengths as a result of their low extensibility and this is related to their terrestrial habit and need for water conservation. ( b ) Amphiporus lactifloreus, Lineus gesserensis and L. longissimus are moderately flattened in the relaxed position and have extensibilities between 6 and 10. They are marine crawling forms using cilia for locomotion and so must present a fairly large ciliated surface to the substratum. The fibre system does not limit contraction; the compression of the epithelial cells causes the observed extensibilities to fall a little short of the theoretical values. ( c ) Cerebratulus lacteus, Malacobdella grossa, Polycelis nigra and Dendrocoelum lacteum are very flattened forms and have very high theoretical extensibilities, but very low observed ones. The factors causing this are the thickness of the body-wall musculature ( Cerebratulus ), the limiting effect of longitudinal and circular reticulin fibres in the muscle layers, and the presence of dorso-ventral and diagonal muscles. Their flattened form is correlated with ecological factors (with swimming in Cerebratulus , with its parasitic life in the mantle of bivalves in Melacobdella ) or with physical ones in turbellarians where a permanently flattened form is necessary for these worms to move by ciliary action.

The absorption and metabolism of some sugars in the locust, Schistocerca gregaria (Forsk.).

Abstract: 1. The uptake of 14 C-labelled glucose, mannose and fructose from the alimentary canal of Schistocerca gregaria (Forsk.) has been studied using the dye Amaranth as a reference substance. 2. Absorption was confined to the mid-gut, the proportion absorbed by the caeca depending on the type of sugar and its concentration in the gut lumen. 3. The absorbed sugars were converted, in varying degrees, to trehalose which accumulated in the haemolymph. The extent of the conversion appeared to parallel the rate of absorption of the sugars at the various concentrations. 4. The sugars passed through the gut wall at similar rates in experiments in which the isolated alimentary canal was suspended in a large volume of circulating poisoned saline. The passage through the gut wall under these conditions was equivalent to the rapid absorption obtained in vivo when there was a rapid conversion to trehalose. 5. It is suggested that these observations support the hypothesis that the sugars are absorbed by diffusion across the gut wall and that the process is facilitated by the rapid conversion to trehalose in the haemolymph, which tends to maintain a steep concentration gradient. 6. At very low concentrations in the gut lumen, glucose was at a similar level to the relatively small amount of glucose in equilibrium with the trehalose in the haemolymph. When the specific activity of injected 14 C in the haemolymph approximated to that in the gut lumen the absorption of the labelled glucose from the mid-gut caeca was reduced at very low concentrations. Thus at these levels it is suggested that most of the absorption of labelled glucose can be attributed to an exchange with that in the haemolymph. At a concentration of 0.01 M/1. the proportion exchanging became negligibly small and the absorption of the labelled glucose molecules approximated to the net glucose absorption.

The Mechanism of Osmotic Regulation in Artemia Salina (L.): The Physiology of the Branchiae

Abstract: 1. The uptake of silver ions by Artemia has been investigated. The staining is localized to the first ten pairs of branchiae. There is no staining of the eleventh pair or of any other part of the animal. The uptake of silver is due to a purely passive precipitation of AgCl within the thickness of the branchial cuticle. 2. The effects of KMnO 4 and methylene-blue solutions have also been studied. Their effect is localized to the epithelium under the cuticle of the first ten pairs of branchiae. 3. It is concluded that all these staining reactions demonstrate that the cuticle over the first ten pairs of branchiae is the only part of the external cuticle that is appreciably permeable. 4. Animals whose branchial epithelium has been damaged by a brief exposure to saturated KMnO 4 solution have lost the ability to osmo-regulate. They are closely isotonic with their medium, and the range of external concentration tolerated is much restricted. 5. This isotonicity is not due simply to increased permeability, but is due to specific destruction of the mechanism normally excreting NaCl in hypertonic media. 6. Correlation of the physiological effects of KMnO 4 treatment with the sharp localization of damage, and the evidence for localized permeability indicates that the epithelium of the first ten pairs of branchiae is the site of active NaCl excretion in hypertonic media, and probably of active uptake from hypotonic media. 7. The ontogeny of this mechanism is traced. In nauplii the dorsal organ is apparently concerned in NaCl excretion. When the branchiae develop the dorsal organ degenerates.

The Mechanism of Gill Ventilation in Three Freshwater Teleosts

Abstract: 1. A study has been made of the respiratory movements of three species of freshwater fish. The time course of pressure changes in the buccal and opercular cavities was recorded and movements of the mouth and operculum plotted from cine films taken simultaneously. 2. Opening and closing of the mouth precede respectively abduction and adduction of the operculum by about one-fifth of a cycle. 3. The most prominent part of the buccal pressure curve is a positive pressure associated with mouth closing. The size of a negative pressure as the mouth opens is small in the trout but may be relatively large in the tench. 4. Abduction of the operculum produces a marked negative pressure in the opercular cavity of all three species and there is a slight positive pressure during its adduction. 5. The respiratory system is divided into a buccal and two opercular cavities and the concept of gill resistances separating them is introduced. 6. The respiratory cycle is made up of four phases which succeed one another. These are: phase (1) opercular suction pump predominant; phase (2) transition with a reduction in differential pressure between the buccal and opercular cavities; phase (3) buccal pressure pump predominant; and phase (4) transition with reversal of differential pressure. 7. With the exception of phase (4), which occupies only about one-tenth of a cycle, the pressure in the buccal cavity exceeds that in the opercular cavity throughout the cycle. It is therefore concluded that water will flow across the gills for almost the entire cycle but may reverse for this brief period. The quantitative relationship between the pressures and the volume of water flowing across the gills during different parts of the cycle will depend upon the properties of the gill resistances.

The Blood Volumes of Some Representative Molluscs

Abstract: 1. Individuals of Cryptochiton stelleri, as representatives of the class Placophora, distributed inulin in blood volumes yielding a mean of 43.8% of the wet body weight without shell. Mean cellular water was estimated to be 76%. 2. The two opisthobranch gastropods examined were found to have very large mean blood volumes. Aplysia californicus distributed haemoglobin in 76.2% and mild silver proteinate in 73.1% of the wet body weight. Inulin was distributed in a significantly larger space averaging 79.3% of the body weight, which probably included pericardial and renal spaces. Archidoris sp. distributed inulin in 65.4% of the wet body weight. Mean cellular waters were 74-79% in Aplysia and 83% in Archidoris. 3. Two pulmonate gastropods were studied with inulin which was distributed in a mean space 40.3% of the wet body weight without shell of Achatina fulica, and 36.6% of the wet body weight in Arion ater. The computed cellular waters were 77 and 79%, respectively. 4. Excellent agreement was shown between a marine pelecypod, Mytilus californianus, and a fresh-water pelecypod, Margaritana margaritifera, of similar body size and form. Inulin in the former was distributed in 50.8%, and in the latter inulin and T-1824 in 49% of the wet body weight without shell. The cellular water contents were 80 and 76%, respectively. 5. In a single representative of the Cephalopoda--Octopus hongkongensis, it was possible to demonstrate with T-1824 and with HgS a blood volume averaging 5.8% of the wet body weight, constituting a fluid space distinctly different from the tissue fluid space. Inulin was distributed in the entire extracellular space amounting to 28% of the wet body weight. The cell water which was calculated from the mean values obtained was 77%.

Osmoregulation in the Muscle Fibres of Carcinus Maenas

Abstract: 1. Measurements have been made of the freezing-point depression of single muscle fibres of Carcinus maenas and of the concentrations of the non-protein nitrogenous components of the muscle. 2. When the blood is diluted the osmotic activity of the muscle fibres always falls in proportion. The fibres are probably always in osmotic equilibrium with the blood. 3. The osmotic activity of the fibres can be accounted for in terms of the concentrations of the muscle ions together with nitrogen-containing compounds, such as free amino acids, taurine and trimethylamine oxide. These organic substances account for over 60% of the total osmotic pressure. 4. In crabs from dilute sea water the concentrations of the nitrogenous compounds are reduced below the level expected from the increase in water content of the muscle. It is suggested that the muscle fibre can prevent excessive water intake by the removal of nitrogenous substances, thus reducing the internal osmotic activity. The process is reversible. 5. The importance of the mechanism in relation to the adaptability of the cell to reduced blood concentration is discussed.

The Movement of the Spermatozoa of the Bull

Abstract: 1. The maximum extent to which an element of the tail of a bull9s spermatozoon bends during its contractile cycle is not the same for all elements; the nearer the element lies towards the tip of the tail the greater is the amount of bending. 2. The phase difference between successive elements varies along the length of the tail; and consequently the speed of propagation of the bending wave decreases as the latter moves backwards. 3. The amplitude of transverse movement relative to the head increases progressively along the tail towards the distal end. 4. Distal elements execute figure-of-eight movements relative to the head. 5. The frequency of the bending cycles and the propulsive velocity of the whole cell vary considerably. The average frequency for thirty-one cells was 9.1/sec., and the average propulsive speed for 235 cells was 94 µsec. 6. Cells moving freely in water ‘flashed’ with a frequency similar to that of the bending waves. The rotation of the head about its longitudinal axis appears to be due to the fact that all elements of the tail are not executing their transverse movements in exactly the same plane during the whole of their contractile cycles. 7. The rate at which an element can propel itself forward cannot be greater than about one-third to one-quarter of its average transverse velocity. 8. The distal elements of the tail exert their propulsive effort against the fulcrum provided by the proximal elements. 9. It is impracticable to relate the speed of propulsion to the form and speed of propagation of the waves passing along the tail.

The Induction and Termination of Facultative Diapause in the Chalcid Wasps Mormoniella Vitripennis (Walker) and Tritneptis Klugii (Ratzeburg)

Abstract: 1. Experiments have been conducted to determine the extrinsic factors that cause facultative diapause in two parasitic chalcid wasps, Mormoniella vitripennis and Tritneptis klugii , and to analyse the mechanism of diapause termination. 2. In both species diapause occurs in the last larval instar after the feeding period has ended and just prior to defaecation. The diagnostic feature of the diapausing larva is that it does not immediately moult into a pupa. 3. In Mormoniella exposing females to low temperature during oogenesis causes their progeny to enter diapause at the end of the last larval instar. Low temperature thus causes the female to lay an egg that is qualitatively different from an ordinary egg in that the larva emerging from it eventually enters diapause. This action of low temperature on the female wears off after several days and the wasp returns to producing non-diapausing offspring. 4. In Tritneptis low temperature also produces diapause, but in this species low temperature, to be effective, must act on the larva itself between the second and final instar to produce diapause in that generation. 5. The diapause of Mormoniella was considered in relation to maternally induced diapause in other species and two possible mechanisms for the action of low temperature were suggested, namely, a direct action on the ovaries or an indirect action through the maternal production of a diapause hormone. 6. It was found that exposure to low temperatures enables larvae of both species to break diapause and complete their development when subsequently placed at 25° C. 7. The mechanism of action of low temperature in terminating diapause was examined in Mormoniella by exposing larvae to various temperature regimes in the presence and absence of oxygen. 8. Ten weeks at 5° C. enabled nearly 90% of the larvae to terminate diapause when returned to 25° C.; after 6 weeks at 5° C. less than 10% developed. Chilling at 2° C. was more effective than 5 or 1o° C., while temperatures above 15 or below -6° C. were ineffective. 9. Although diapause was never terminated by keeping larvae continually at temperatures above 15° C., a period of exposure to temperatures above 15° C. prior to chilling decreased the amount of chilling necessary to terminate diapause. 10. Larvae chilled in the absence of oxygen for as long as 28 weeks failed to break diapause but developed when subsequently rechilled in air. 11. After receiving a threshold exposure to low temperature larvae could not be returned to diapause by temperature shocks as high as 45° C.; however, the effects of subthreshold chilling were reversed by exposure to 25° C. Thus, animals chilled for a total of 20 weeks, with 1 week of warming after each week of chilling, failed to develop. Similarly, it was found that interrupting 8 weeks of chilling on the 25th day by 4 days of warming partially undid the chilling. 12. When warming was conducted in the absence of oxygen it failed to undo the effects of subthreshold chilling and the termination of diapause was markedly accelerated. Indeed, when larvae were chilled for a subthreshold period, a brief interval of anaerobic warming sufficed to enable some of the larvae to terminate diapause. 13. In addition to the above, a variety of other experiments were conducted with alternating periods of chilling and warming in the presence and absence of oxygen. These led to a hypothesis which seems to account for the action of low temperature in terminating larval diapause. 14. The hypothesis focuses attention on the neurosecretory cells of the insect9s brain and suggests that low temperature slows down an aerobic breakdown reaction within the larval brain and permits the synthesis of a substance necessary for neurosecretory activity. The initial stages of the synthetic reaction are aerobic but later stages are favoured by anaerobic warming. The nature of these reactions was discussed.

The Migration of Spermatozoa in the Female of Rhodnius Prolixus Stal

Abstract: 1. Removal of the opaque accessory glands from a male Rhodnius prevents the normal migration of the spermatozoa in a female which is inseminated by it. 2. The opaque accessory secretion induces rhythmic contractions in the oviducts, probably by acting through a peripheral nervous system. 3. Paralysis of the muscles of the female without interfering with the motility of the spermatozoa prevents the ascent of the spermatozoa. 4. Killing the spermatozoa in the bursa has no effect on their subsequent migration. 5. The central nervous system is not essential for the migration. 6. It is concluded that the migration of spermatozoa in the female of Rhodnius proxlixus is a result of rhythmic contractions set up in the oviduct by the opaque accessory secretion of the male acting through a peripheral nervous system. Evidence in the literature suggests that the mechanism may operate in a number of spermatophore-forming species.

Effects of the ant, Lasius niger L., on the feeding and excretion of the bean aphid, Aphis fabae Scop

Abstract: 1. To test the idea of Herzig (1937) that the excretion and feeding rates of aphids are stimulated by attendant ants, bean plants ( Vicia faba ), on which groups of nymphs of Aphis fabae were feeding, were made radioactive with 32 P in water culture, so that the aphids took up the isotope and excreted it in their honeydew. The radioactivity of the honeydew taken from them by attendant Lasius niger was then compared with that of the honeydew excreted concurrently by unattended control aphids on separate plants. 2. By increasing their uptake of plant sap the ant-attended aphids produced twice as much radioactivity in their excreta as did the ant-free aphids. 3. The aphids directly control their rates of excretion and feeding, which are not determined solely by forces within the plant. 4. The aphid apparently controls its feeding by the ‘sucking pump’ in its head. It is suggested that the pump is normally closed but that periodically it opens to admit sap into its lumen and then closes ventrally to force the ingested sap into the stomach. During normal feeding the pump probably opens and closes at regular intervals; but when the aphid is ant-attended it could operated more frequently so as to force sap into the stomach more often. The uptake of sap by normally feeding aphids is apparently not continuous.

The Effect of Temperature on the Water-Proofing Mechanism of an INSECT

Abstract: 1. Previous methods for determining the temperature characteristics of the permeability to water of insect cuticle are criticized on five fundamental points, and in particular it is shown that they do not measure the temperature of the cuticle which will be substantially different from that of the surrounding air. 2. The physical principles for accurate measurement are outlined, involving the accurate control of air temperature and air circulation, the measurement of cuticle temperature and of water loss within a sealed enclosure, and the assessment of true saturation deficiency. Apparatus for meeting these requirements and making these measurements is described. 3. Determinations have been made of the permeability of the cuticle of Periplaneta americana nymphs. When the permeability is plotted against cuticle temperature a sudden and substantial increase in permeability is seen to take place at around 30° C. The temperature at which this change occurs is higher the longer the time which has elapsed since the nymph previously moulted. 4. A method of measuring the permeability of the cuticular grease, when spread as a layer over an isolated water droplet, is described. This layer, whose thickness is of molecular dimensions, has much greater absolute impermeability to water than the thick grease on the insect. It also exhibits a sudden increase in permeability at about 30° C., and the order of change is considerably greater than that found with intact cuticle. 5. The findings are quantitatively compatible with the postulate that, at lower temperatures, the grease on the cockroach consists of an orientated ‘monolayer’ organized by the attraction of its polar groupings for the aqueous cuticle surface underlying it, together with a much greater thickness of unorganized grease above it. In absolute units, the grease is about five times as permeable to water as is the ‘monolayer’, but at the transition temperature the measurements agree with the supposition that the molecular organization of the ‘monolayer’ breaks down into the disorganized state of the major part of the grease with a corresponding increase in permeability. 6. The suggestion that films of grease on water, and the lowermost portion of the grease on the animal, have orientated molecular organization is supported by some observations on the effect of dust particles on the films and by information previously published.

The Mechanism of Osmotic Regulation in Artemia Salina (L.): The Physiology of the Gut

Abstract: 1. Artemia is continuously swallowing its medium, whether it is hyper-, iso-, or hypotonic to the haemolymph, and taking up water from the gut lumen. 2. The osmotic pressure of the gut fluids is appreciably greater than that of the haemolymph, but in the more concentrated media is considerably below that of the medium. This indicates that considerable amounts of NaCl must be passing across the gut epithelium into the haemolymph. 3. The concentration of both sodium and chloride ions in the gut fluids is always less than that in the haemolymph, indicating that there must be an active uptake of NaCl across the gut epithelium. 4. It is considered that the gut of Artemia has become adapted as a mechanism for the active uptake of water, controlling water balance and preventing dehydration in hypertonic media. 5. The adaptations for maintaining the NaCl and the water balances in Artemia are compared to those found in the marine teleosts, and are shown to be extremely similar.

The Survival of Artemia Salina (L.) in Various Media

Abstract: 1. The survival of Artemia salina adults in various media has been studied. 2. Prolonged survival is only possible in media in which certain sodium salts (principally NaCl) predominate. 3. Certain substances are found to be highly toxic. 4. It is confirmed that the high toxicity of potassium ions can be antagonized by sodium ions. 5. The results indicate that the animal is appreciably permeable.

Oxygen Consumption as a Function of Size and Salinity in Metapenaeus monoceros Fab. From Marine and Brackish-Water Environments

Abstract: 1. The oxygen consumption in relation to the salinity of the medium has been studied in a marine and a brackish-water population of the prawn, Metapenaeus monoceros Fab. 2. It has been shown that the regression coefficient of oxygen consumption against weight is not the same for media of different salinity and for the two populations. 3. In both the groups of prawns an increase in the oxygen consumption was observed, with a decrease in the salinity of the medium below that of the habitat. But the marine prawns showed higher rates in 50 and 25% sea water compared to the brackish-water prawns. On the other hand, the brackish-water prawns exhibited a higher rate of oxygen consumption in 100% sea water and in tap water. 4. It is suggested that these differences might be due to (i) an osmotic adaptation, and (ii) the operation of a metabolic homoeostatic mechanism in relation to osmotic regulation.

Observations on the Temperature Regulation and Food Consumption of Honeybees (Apis Mellifera)

Abstract: 1. Bees have been kept in groups whose numbers ranged from 10 to 200 bees, at temperatures ranging from 0-40° C. 2. At 40° C. bees in groups of 200 had a higher death-rate than bees in smaller groups. At temperatures of 25-35° C. the death-rate was low and about the same in all groups . Below 25° C. the more bees in a group, the longer they survived. 3. The temperatures of all groups increased with that of their environment, the larger a group, the higher its temperature. The difference between the external temperature and that of the groups decreased with increase in the former until at 35 and 40° C. groups of all sizes were at or slightly below environmental temperature. 4. At temperatures from 20-40° C. the percentage of bees in a group that were clustering was directly related to the size of their group, bees in groups of 10 or 25 hardly clustering at all. At each temperature at 15° C. or below, about the same high percentage of bees clustered in all groups. 5. The amount of food (sugar syrup) consumed per bee increased with decrease in the environmental temperature. Very little water was drunk at environmental temperatures of 25° C. or lower but, at 35° C. and above, relatively enormous quantities were taken. 6. These results have been discussed especially in relation to information on the temperature regulation and food consumption of colonies in winter. RESP-4055

Studies on the Feeding and Nutrition of Tuberolachnus Salignus (Gmelin) (Homoptera, Aphididae) : III. The Nitrogen Economy

Abstract: 1. The investigation concerns the ingestion, excretion, and assimilation of dietary nitrogen by Tuberolachnus salignus (Gmelin) developing on Salix trees in various stages of leaf development. 2. Apterous and alate forms of T. salignus differ in their rates of development and nitrogen assimilation and in their behaviour. 3. The aphids assimilate considerably more nitrogen when developing on willows having a phloem sap rich in nitrogen than on willows having a phloem sap relatively poor in nitrogen. 4. For a given amount of nitrogen assimilated the aphids ingest a larger volume of a phloem sap poor in nitrogen than of a phloem sap rich in nitrogen. 5. Nitrogen balance experiments have shown that T. salignus nymphs assimilate only as much nitrogen as they are able to absorb from their food. 6. The evidence for and against the fixation of atmospheric nitrogen by aphids through the agency of their symbionts is briefly discussed. T. salignus do not supplement their dietary nitrogen supply by fixing atmospheric nitrogen.

Some Experiments on Form Perception in the Nymphs of the Desert Locust, Schistocerca Gregaria Forskål

Abstract: 1. Nymphs of the desert locust are spontaneously attracted to simple forms in the visual environment, and show a preference for certain figures. 2. Experiments are described which analyse certain of the important properties which make a figure attractive to this insect. The insects show a preference for long straight vertical edges as opposed to short straight vertical edges. Straight vertical edges are preferred to straight oblique edges and vertical figures with straight edges are preferred to vertical figures with wavy or serrated edges. In the absence of straight vertical edges a preference is shown for the figure with the more complex contour (for figures of comparable size). 3. It is postulated that in this insect form discrimination is based on the number of stimulus changes per unit time produced by moving contours and on the spatial and temporal distribution of such changes. 4. The results are compared with those of previous workers and in particular with those of Hertz and of Wolf and Zerrahn-Wolf on the bee.