Showing papers in "Philosophical Transactions of the Royal Society B in 1984"

The Limits to Peat Bog Growth

Abstract: Not less than 2% of the Earth's land surface is peat-covered, so it is important to try to understand the dynamics of peat accumulation. Peat-forming systems (mires) accumulate peat because conditions within them impede the decay of the plant material produced by their surface vegetation. This paper concerns the rate of peat production and some unexpected consequences of the processes of decay. These consequences are likely to be of interest to those concerned with mire ecology and with the history of vegetation during Flandrian times. Most peat-forming systems consist of two layers: an upper 10-50 cm deep aerobic layer of high hydraulic conductivity, the acrotelm, in which the rate of decay is relatively high; and a thicker, usually anaerobic, lower layer, the catotelm, of low conductivity and with a much lower rate of decay. Plant structure at the base of the acrotelm collapses as a consequence of aerobic decay, and the hydraulic conductivity consequently decreases. As long as precipitation continues the water table therefore rises to this level, thus engulfing material at the base of the acrotelm. The rate, p $\_c$ , of this input to the catotelm is exactly analogous to the rate, p $\_a$ , of input to the acrotelm i.e. of primary productivity of the vegetation. During passage through the acrotelm the peat becomes richer in the more slowly decaying components. The depth of, and the time for transit through, the acrotelm thus control p $\_c$ . The catotelm, however, usually forms much the largest part of the peat mass. Selective decay may continue in the catotelm. The specific composition of the peat thus becomes a progressively poorer indicator of the surface vegetation that formed it, and to a degree that is not generally realized: reconstructions of the past surface vegetation may become very inaccurate. If p $\_c$ were constant and there were no decay in the catotelm then for the centre of a peat bog the profile of age against depth (measured as cumulative mass below the surface) would be a straight line. But if either or both these conditions is untrue then the profile would probably be concave. Most of the cases for which data exist are consistent with a concave profile and a value (constant over several thousand years) of p $\_c$ of about 50 g m $^{-2}$ a $^{-1}$ and a decay rate coefficient, $\alpha\_c$ , proportional to the amount of mass remaining, of about 10 $^{-4}$ a $^{-1}$ . This rate of input to the catotelm is about 10% of the primary productivity i.e. about 90% of the matter is lost during passage through the acrotelm. The relation seems to hold in spite of short-term fluctuations such as those represented by recurrence surfaces. Although 10 $^{-4}$ a $^{-1}$ seems a very slow rate, it has important consequences. (i) The peat mass tends towards a steady state in which the rate of addition of matter at the surface, p $\_a$ , is balanced by losses at all depths: the rate of accumulation is zero. This depth is, for the cases examined, about 5-10 m. (ii) The very concept of \`peat accumulation rate' thus needs careful consideration. To calculate it as the difference between two $^{14}$ C dates divided by the depth between the samples from which they were measured, as is commonly done, may be seriously misleading. The error is likely to increase with age, depth and time span. (iii) Progress in such studies can be made only if the easily measured profile of bulk density is known. The position of the profile in the peat bog must also be known. There is some evidence that peat contains, or comes to contain, about 1% or less of the original mass in a highly refractory state, so that the concept of a steady state is unlikely to be correct if times much greater than about 50 000 years are involved. Three more consequences of the continued very slow decay in the catotelm may be of interest to mire ecologists. (iv) Most of the mass that leaves the catotelm probably does so as methane gas. The concentration of methane increases with depth and may be as high as 5 $\mu mol$ cm $^{-3}$ at 5 m depth (about 10% by volume). Diffusion alone is able to remove mass at the necessary rate and would create concentration profiles similar to those observed. The solubility of methane in water is exceeded, however, and much of the methane may in practice be lost by mass flow of bubbles to the surface. (v) The amplitude of temperature fluctuations, as well as the mean temperature, may have a significant effect on the rate of peat decay, particularly in a cold climate. (vi) If this analysis is correct then the maximum depth of peat which can accumulate in 50 000 years is determined largely by the value of the quotient p $\_c$ / $\alpha\_c$ . The usual view that the maximum depth is determined directly by climate operating through hydrology may be incorrect, though hydrology may have an indirect effect on the value of p $\_c$ , the rate of input to the catotelm at the bog centre. Away from the centre p $\_c$ is probably variable p $\_c$ and determined by hydrology. Its dependence on distance from the centre and on time is complicated: p $\_c$ /p $\_c$ may be more than, equal to, or less than 1.0. The age against depth profile away from the bog centre may be directly affected by hydrology, though the effect is not large except near the edge of the bog or near the base of the peat. There may, of course, be catastrophic failure - a bog-burst or \`flow' - before the p $\_c$ / $\alpha\_c$ limit is reached in the centre, or slower but equally destructive development of gullies and erosion.

The Aerodynamics of Hovering Insect Flight. III. Kinematics

Abstract: Insects in free flight were filmed at 5000 frames per second to determine the motion of their wings and bodies. General comments are offered on flight behaviour and manoeuvrability. Changes in the tilt of the stroke plane with respect to the horizontal provides kinematic control of manoeuvres, analogous to the type of control used for helicopters. A projection analysis technique is described that solves for the orientation of the animal with respect to a cam era-based coordinate system, giving full kinematic details for the longitudinal wing and body axes from single-view films. The technique can be applied to all types of flight where the wing motions are bilaterally symmetrical: forward, backward and hovering flight, as well as properly banked turns. An analysis of the errors of the technique is presented, and shows that the reconstructed angles for wing position should be accurate to within 1-2° in general. Although measurement of the angles of attack was not possible, visual estimations are given. Only 11 film sequences show flight velocities and accelerations that are small enough for the flight to be considered as ‘hovering’. Two sequences are presented for a hover-fly using an inclined stroke plane, and nine sequences of hovering with a horizontal stroke plane by another hover-fly, two crane-flies, a drone-fly, a ladybird beetle, a honey bee, and two bumble bees. In general, oscillations in the body position from its mean motion are within measurement error, about 1-2 % of the wing length. The amplitudes of oscillation for the body angle are only a few degrees, but the phase relation of this oscillation to the wingbeat cycle could be determined for a few sequences. The phase indicates that the pitching moments governing the oscillations result from the wing lift at the ends of the wingbeat, and not from the wing drag or inertial forces. The mean pitching moment of the wings, which determines the mean body angle, is controlled by shifting the centre of lift over the cycle by changing the mean positional angle of the flapping wings. Deviations of the wing tip path from the stroke plane are never large, and no consistent pattern could be found for the wing paths of different insects; indeed, variations in the path were even observed for individual insects. The wing motion is not greatly different from simple harmonic motion, but does show a general trend towards higher accelerations and decelerations at either end of the wingbeat, with constant velocities during the middle of half-strokes. Root mean square and cube root mean cube angular velocities are on average about 4 and 9% lower than simple harmonic motion. Angles of attack are nearly constant during the middle of half-strokes, typically 35° at a position 70 % along the wing length. The wing is twisted along its length, with angles of attack at the wing base some 10-20° greater than at the tip. The wings rotate through about 110° at either end of the wingbeat during 10-20 % of the cycle period. The mean velocity of the wing edges during rotation is similar to the mean flapping velocity of the wing tip and greater than the flapping velocity for more proximal wing regions, which indicates that vortex shedding during rotation is com parable with that during flapping. The wings tend to rotate as a flat plate during the first half of rotation, which ends just before, or at, the end of the half-stroke. The hover-fly using an inclined stroke plane provides a notable exception to this general pattern : pronation is delayed and overlaps the beginning of the downstroke. The wing profile flexes along a more or less localized longitudinal axis during the second half of rotation, generating the ‘flip’ profile postulated by Weis-Fogh for the hover-flies. This profile occurs to some extent for all of the insects, and is not exceptionally pronounced for the hover-fly. By the end of rotation the wings are nearly flat again, although a slight camber can sometimes be seen. Weis-Fogh showed that beneficial aerodynamic interference can result when the left and right wings come into contact during rotation at the end of the wingbeat. His ‘fling’ mechanism creates the circulation required for wing lift on the subsequent half-stroke, and can be seen on my films of the Large Cabbage White butterfly, a plum e moth, and the Mediterranean flour moth. However, their wings ‘peel’ apart like two pieces of paper being separated, rather than fling open rigidly about the trailing edges. A ‘partial fling’ was found for some insects, with the wings touching only along posterior wing areas. A ‘ near fling ’ with the wings separated by a fraction of the chord was also observed for m any insects. There is a continuous spectrum for the separation distance between the wings, in fact, and the separation can vary for a given insect during different manoeuvres. It is suggested that these variants on Weis-Fogh’s fling mechanism also generate circulation for wing lift, although less effectively than a complete fling, and that changes in the separation distance may provide a fine control over the amount of lift produced.

The Aerodynamics of Hovering Insect Flight. I. The Quasi-Steady Analysis

Abstract: The conventional aerodynamic analysis of flapping animal flight invokes the `quasisteady assumption' to reduce a problem in dynamics to a succession of static conditions: it is assumed that the instantaneous forces on a flapping wing are equivalent to those for steady motion at the same instantaneous velocity and angle of attack. The validity of this assumption and the importance of unsteady aerodynamic effects have long been controversial topics. Weis-Fogh tested the assumption for hovering animal flight, where unsteady effects are most pronounced, and concluded that most insects indeed hover according to the principles of quasi-steady aerodynamics. The logical basis for his conclusion is reviewed in this paper, and it is shown that the available evidence remains ambiguous. The aerodynamics of hovering insect flight are re-examined in this series of six papers, and a conclusion opposite to Weis-Fogh's is tentatively reached. New morphological and kinematic data for a variety of insects are presented in papers II and III, respectively. Paper IV offers an aerodynamic interpretation of the wing kinematics and a discussion on the possible roles of different aerodynamic mechanisms. A generalized vortex theory of hovering flight is derived in paper V, and provides a method of estimating the mean lift, induced power and induced velocity for unsteady as well as quasi-steady flight mechanisms. The new data, aerodynamic mechanisms and vortex theory are all combined in paper VI for an analysis of the lift and power requirements and other mechanical aspects of hovering flight. A large number of symbols are needed for the morphological, kinematic and aerodynamic analyses. Most of them appear in more than one paper of the series, and so a single comprehensive table defining the major symbols from all of the papers is presented at the end of this paper.

The Aerodynamics of Hovering Insect Flight. II. Morphological Parameters

Abstract: Morphological parameters are presented for a variety of insects that have been filmed in free flight. The nature of the parameters is such that they can be divided into two distinct groups: gross parameters and shape parameters. The gross parameters provide a very crude, first-order description of the morphology of a flying animal: its mass, body length, wing length, wing area and wing mass. Another gross parameter of the wings is their virtual mass, or added mass, which is the mass of air accelerated and decelerated together with the wing at either end of the wingbeat. The wing motion during these accelerations is almost perpendicular to the wing surface, and the virtual mass is approximately given by the mass of air contained in an imaginary cylinder around the wing with the chord as its diameter. The virtual mass ranges from 0.3 to 1.3 times the actual wing mass, indicating that the total mass accelerated by the flight muscles can be more than twice the wing mass itself. Over the limited size range of insects in this study, the interspecific variation of non-dimensional forms of the gross parameters is much greater than any systematic allometric variation, and no interspecific correlations can be found. The new shape parameters provide quite a surprise, however: intraspecific coefficients of variation are very low, often only 1%, and interspecific allometric relations are extremely strong. Mechanical aspects of flight depend not only on the magnitude of gross morphological quantities, but also on their distributions. Non-dimensional radii are derived from the non-dimensional moments of the distributions; for example, the first radius of wing mass about the wing base gives the position of the centre of mass, and the second radius corresponds to the radius of gyration. The radii are called \`shape parameters' since they are functions only of the normalized shape of the distributions, and they provide a second-order description of the animal morphology. The various radii of wing area are strongly correlated, as are those of wing mass and of virtual mass: the higher radii for each quantity can all be expressed by allometric functions of the first radius. The overall shape of the distribution of a quantity can therefore be characterized by a single parameter, the position of the centroid of that quantity. The strong relations between the radii of wing area, mass and virtual mass hold for a diverse collection of insects, birds and bats. Thus flying animals adhere to \`laws of shape' regardless of biological differences. Aerodynamic and mechanical considerations are most likely to provide an understanding of these laws of shape, but an explanation has proved elusive so far. The detailed shape of a distribution can be reconstructed from the shape parameters by matching the moments of the observed distribution to those of a suitable analytical function. A Beta distribution is compared with the distribution of wing area, i.e. the shape of the wing, and a very good fit is found. With use of the laws of shape relating the higher radii to the first radius, the Beta distribution can be reduced to a function of only one parameter, thus providing a powerful tool for drawing a close approximation to the entire shape of a wing given only its centroid of area. Quite unexpectedly, the continuous spectrum of wing shapes can then be described in detail by a single parameter of shape.

High Efficiency Gene Transfer into Mammalian Cells

Abstract: We have generalized the protocol of gene transfer, greatly increasing the variety of cells that can be used as recipients of foreign genes. Our approach has been to use a transient assay system that allows rapid screening of expression of foreign DNA. When the initial steps of gene transfer have been optimized with the transient system, these defined conditions are used to yield efficient stable transformation. We have seen that primate cells, including human cells, can be used in gene transfer experiments at levels sensitive enough to allow detection of single copy gene function. Recently we have also used this approach successfully with undifferentiated embryonic cells.

The Aerodynamics of Hovering Insect Flight. IV. Aeorodynamic Mechanisms

Abstract: A full derivation is presented for the vortex theory of hovering flight outlined in preliminary reports. The theory relates the lift produced by flapping wings to the induced velocity and power of the wake. Suitable forms of the momentum theory are combined with the vortex approach to reduce the mathematical complexity as much as possible. Vorticity is continuously shed from the wings in sympathy with changes in wing circulation. The vortex sheet shed during a half-stroke convects downwards with the induced velocity field, and should be approximately planar at the end of a half-stroke. Vorticity within the sheet will roll up into complicated vortex rings, but the rate of this process is unknown. The exact state of the sheet is not crucial to the theory, however, since the impulse and energy of the vortex sheet do not change as it rolls up, and the theory is derived on the assumption that the extent of roll-up is negligible. The force impulse required to generate the sheet is derived from the vorticity of the sheet, and the mean wing lift is equal to that impulse divided by the period of generation. This method of calculating the mean lift is suitable for unsteady aerodynamic lift mechanisms as well as the quasi-steady mechanism. The relation between the mean lift and the impulse of the resulting vortex sheet is used to develop a conceptual artifice - a pulsed actuator disc - that approximates closely the net effect of the complicated lift forces produced in hovering. The disc periodically applies a pressure impulse over some defined area, and is a generalized form of the Froude actuator disc from propeller theory. The pulsed disc provides a convenient link between circulatory lift and the powerful momentum and vortex analyses of the wake. The induced velocity and power of the wake are derived in stages, starting with the simple Rankine-Froude theory for the wake produced by a Froude disc applying a uniform, continuous pressure to the air. The wake model is then improved by considering a `modified' Froude disc exerting a continuous, but non-uniform pressure. This step provides a spatial correction factor for the Rankine-Froude theory, by taking into account variations in pressure and circulation over the disc area. Finally, the wake produced by a pulsed Froude disc is analysed, and a temporal correction factor is derived for the periodic application of spatially uniform pressures. Both correction factors are generally small, and can be treated as independent perturbations of the Rankine-Froude model. Thus the corrections can be added linearly to obtain the total correction for the general case of a pulsed actuator disc with spatial and temporal pressure variations. The theory is compared with Rayner's vortex theory for hovering flight. Under identical test conditions, numerical results from the two theories agree to within 3%. Rayner presented approximations from his results to be used when applying his theory to hovering animals. These approximations are not consistent with my theory or with classical propeller theory, and reasons for the discrepancy are suggested.

Ferritin: Design and Formation of an Iron-Storage Molecule

Abstract: Although essential for most forms of life, too much iron is harmful. To cope with these antagonistic phenomena an iron-storage molecule, ferritin, has evolved. The structure of horse spleen apoferritin, which has recently been refined, consists of 24 symmetrically related subunits forming a near-spherical hollow shell. In ferritin the central cavity is occupied by an iron core of 'ferrihydrite', a geologically ephemeral mineral found in hot or cold springs and in mine workings, or produced in the laboratory by heating solutions of ferric salts. Ferritin itself forms most readily from apoferritin, in the presence of dioxygen, from FeII, not FeIII. Access to its interior is through small intersubunit channels, and the protein influences both the rate of FeII-oxidation and the form of oxide produced.

Wheat storage proteins: their genetics and their potential for manipulation by plant breeding

Abstract: The genes that code for endosperm storage proteins occur at nine complex loci on six different chromosomes. Glu-A1, Glu-B1 and Glu-D1 contain the genes for high molecular mass subunits of glutenin and are close to the centromere on the long arms of chromosomes 1A, 1B and 1D respectively. On the short arms of the same chromosomes, but distant from the centromere, are Gli-A1, Gli-B1 and Gli-D1. Each of these loci carry three major gene families coding for $\omega$ -gliadins, $\gamma$ -gliadins and low molecular mass glutenin subunits. The remaining loci, Gli-A2, Gli-B2 and Gli-D2 occur near the ends of the short arms of chromosomes 6A, 6B and 6D respectively and each code for $\alpha$ - and $\beta$ -gliadins. Recombination of genes within a locus is very rare and has so far been detected only at Glu-B1, at the rate of about one recombinant in 1000 progeny. Each locus displays allelic variation and this is responsible for differences among varieties in protein quality for making bread. The protein variants that are associated with good quality are being identified, firstly by analysing segregating populations and secondly from the development of near-isogenic lines. Current, incomplete, information on the relative qualities of different alleles at each locus indicates the following order of importance: Glu-1 > Gli-1 > Gli-2. Landraces of primitive agriculture are being screened for novel proteins. The genes for some of them are being incorporated into the genomes of commercial wheats.

The Aerodynamics of Hovering Insect Flight. VI. Lift and Power Requirements

Abstract: The lift and power requirements for hovering insect flight are estimated by combining the morphological and kinematic data from papers II and III with the aerodynamic analyses of papers IV and V. The lift calculations are used to evaluate the importance in hovering of two distinct types of aerodynamic mechanisms: (i) the usual quasi-steady mechanism, where the circulation for lift is primarily determined by translation of the wing, and (ii) rotational mechanisms, where the circulation is largely governed by wing rotation at either end of the wingbeat. Power estimates are compared with the available measurements of metabolic rate during hovering to investigate the role of elastic energy storage, the maximum mechanical power output of the flight muscles, and the muscle efficiency. The quasi-steady mechanism proves inadequate for the lift requirements of hover-flies using an inclined stroke plane, and for a ladybird beetle and a crane-fly hovering with a horizontal stroke plane. Observed angles of attack rule out lift enhancement by unsteady modifications to the quasi-steady mechanism, such as delayed stall, but the rotational lift mechanisms proposed in paper IV seem consistent with the kinematics. The rotational mechanisms rely on concentrated vortex shedding from the leading edge during rotation, with attachment of that vorticity as a leading edge separation bubble during the subsequent half-stroke. Strong leading edge vortex shedding should result from delayed pronation for the hover-fly, a near fling and partial fling for the ladybird, and profile flexion for the crane-fly (the flex mechanism). The kinematics for the other insects hovering with a horizontal stroke plane are basically the same as for the anomalous crane-fly, and the quasi-steady mechanism cannot be accepted for them while rejecting it for the crane-fly. All of these insects flex their wings in a similar manner during rotation, and could use the flex mechanism for lift generation. The implication is that most, if not all, hovering animals do not rely on quasi-steady aerodynamics, but use rotational lift mechanisms instead. It is not possible to reconcile the power estimates with the commonly accepted values of both the mechanochemical efficiency of insect flight muscle (about 25%) and its maximum mechanical power output (about 20 W N $^{-1}$ of muscle). Maximum efficiencies of 12-29% could be obtained only if there is no elastic storage of the kinetic energy of the flapping wings, but this would require more than twice the accepted value for maximum mechanical power output. The available evidence suggests that substantial elastic storage does occur, and that the maximum mechanical power output is close to the accepted value. If so, then the efficiency of both fibrillar and non-fibrillar flight muscle is likely to be only 5-9%.

Cytochrome oxidase patches: a new cytoarchitectonic feature of monkey visual cortex.

Abstract: In normal macaque monkeys a histochemical stain for cytochrome oxidase activity revealed a striking pattern of regularly spaced patches in primary visual (striate, area 17, V1) cortex. The patches were most obvious in layers II and III, but also in layers I, IVb, V and VI; only in layers IVc and IVa were they absent. The patches were oval shaped, about 250 by 150 $\mu m$ and aligned into rows spaced about 350 $\mu m$ apart. Along each row a patch was located about every 550 $\mu m$ ; often patches in neighbouring rows were aligned, creating a square array. Their density was about one patch per 0.2 mm $^2$ (550 by 350 $\mu m$ ) in opercular cortex. The patches were also labelled preferentially by stains for lactate dehydrogenase, succinate dehydrogenase, acetylcholinesterase (AChE), and myelin. In V2, a coarser pattern of broad parallel stripes labelled by cytochrome oxidase, lactate dehydrogenase, and AChE was present. The cytochrome oxidase patches were absent in non-primate species like the cat, mink, tree shrew, mouse, rat, rabbit, and ground squirrel. However, they were present in all primate species examined, including the rhesus, cynomolgus, owl, and squirrel monkey, baboon, bushbaby, and human. While more species should be tested, it appears that the patches are a cytoarchitectonic feature unique to primate visual cortex. In the owl monkey patches of anterogradely transported horseradish peroxidase (HRP) were found in layers IVc $\_\alpha$ , III, and II after injection of the tracer into the lateral geniculate nucleus (l.g.n.). They coincided exactly with the position of patches in adjacent sections processed for cytochrome oxidase. A similar result was obtained in the macaque, except that patches were not present in layer IVc $\_\alpha$ . These experiments established that the cytochrome oxidase patches receive a direct, patchy projection from the lateral geniculate body. However, retrogradely filled layer VI cells in the owl monkey bore no regular relation to the patches. In the macaque, the honeycomb' of geniculate terminals in layer IVa matched a similar honeycomb pattern of cytochrome oxidase staining. In the Nissl stain three sublayers in layer IVa were identified: the honeycomb was located in layer IVa $\_\beta$ . In V2, in the owl monkey the parallel stripes of enhanced cytochrome oxidase activity received a direct projection from l.g.n. or pulvinar. In the macaque, after intraocular injection of [ $^3$ H]proline, the rows of patches in layers II and III lay in register with ocular dominance columns seen by transneuronal radioautography in layer IVc. In another macaque, one eye was removed and the cortex stained for cytochrome oxidase, AChE and Nissl substance after six months survival. In layer IVc light and dark bands corresponding to the ocular dominance columns were visible; surprisingly the dark cytochrome oxidase bands matched the light AChE and Nissl bands. The set of bands belonging to the missing eye was determined by examining cytochrome oxidase staining and proline radioautographs in another macaque that sustained severe eye injury by [ $^3$ H]proline injection. In striate cortex, bands of radioactive label from the injured eye matched ocular dominance columns appearing more lightly stained by cytochrome oxidase. In the macaque tested six months after enucleation, in every other row the cytochrome oxidase patches appeared pale and shrunken. These lighter rows fit into precise register with the lighter ocular dominance columns in layer IVc, confirming the correspondence between rows of patches and ocular dominance columns demonstrated by proline injection. AChE staining of patches was similarly affected by eye removal. The effect of visual deprivation upon cytochrome oxidase staining was tested in two monocularly sutured macaques. In the l.g.n. no effect was detected. In visual cortex wide light columns alternating with thin dark columns were observed in layer IV. In one macaque the ocular dominance columns were labelled independently by HRP injection into a deprived l.g.n. lamina. The HRP labelled ocular dominance columns fit within the pale cytochrome oxidase columns; this establishes that monocular deprivation causes a relatively greater loss of enzyme activity in ocular dominance columns belonging to the closed eye. However, there was also loss of cytochrome oxidase staining along the borders of the normal eye dominance columns, indicating that ocular dominance columns in layer IV are subdivided into core zones flanked by border strips that are susceptible to loss of cytochrome oxidase activity with suture of either eye. The core zones are the same width as the rows of cytochrome oxidase patches and correspond to the dark bands seen in Liesegang stains of normal macaque striate cortex. In two adult cats the effect of monocular lid suture at 28 d old was assessed: no effect upon cytochrome oxidase staining in l.g.n. or cortex was observed. The optic disc representation in visual cortex was studied by 2-deoxyglucose radioautography and cytochrome oxidase staining after eye removal or lid suture in macaque monkeys. It appeared as a pale oval, 1.65 times longer than the optic disc, a distortion probably required to maintain overall isotrophy in magnification factor. Patches were present in the disc representation although ocular dominance columns are absent: they appeared rounder and more widely separated. In the temporal cresent patches were also present. They were larger, rounder, and less densely spaced than patches in binocular cortex. Deoxyglucose mapping in a macaque monkey monocularly stimulated with a display of parallel black and white stripes of irregular width and spacing rotated through all orientations has resulted in patches in the upper layers over ocular dominance columns corresponding to the open eye. These patches match cytochrome oxidase patches situated in every other row, thus suggesting that cells located in cytochrome oxidase patches respond to all orientations of stimulus. Macaques binocularly stimulated with vertical or horizontal stripes show a complicated pattern of deoxyglucose uptake, overlapping extensively with the pattern of cytochrome oxidase patches. In one monkey the right eye was removed and 18 d later the animal was stimulated with vertical stripes. Deoxyglucose radioautography and cytochrome oxidase staining combined in single tissue sections each revealed a matching pattern of ocular dominance columns in layer IV. In the upper layers, dots of radioautographic label were present, matching cytochrome oxidase patches in alternate rows. In foetal monkeys at E142-144 the laminar pattern of cytochrome oxidase staining in visual cortex was remarkable for a prominent wide band of intense activity in layer IVb and upper IVc $\_\alpha$ , absent in mature macaques. In tangential section, patches were visible in layers II, III and in layer IVb-IVc $_\alpha$ , which indicates that patches form in monkey visual cortex before birth. The functional significance of the patches remains uncertain. It has been suggested that the visual field is analysed in visual cortex by small modules containing several hypercolumns of each stimulus variable. The cytochrome oxidase patches may constitute the anatomical correlate of these proposed modules.

Macromolecules in mollusc shells and their functions in biomineralization

Abstract: Mollusc shells are used as a model for studying ‘organic-matrix -mediated’ biomineralization, in which crystals are nucleated and grow in a pre-formed structural framework composed of proteins and polysaccharides. In particular, the possibility that the organic matrix functions as a template for crystal formation by epitaxial growth, is examined. In general, individual organic matrix sheets are composed of a thin layer of β-chitin sandwiched between layers of proteins adopting the antiparallel β-sheet conformation. The protein polypeptide chains are oriented perpendicular to the chitin fibrils. The matrix surfaces contain acidic proteins and polysaccharides. X -ray and electron diffraction patterns of matrices and mineral crystals from the nacreous layers of a bivalve, a gastropod and the cephalopod, Nautilus , show that the chitin fibres and the protein polypeptide chains are aligned with the a and b aragonite crystallographic axes, respectively. This strongly suggests that the mineral formed epitaxially upon the matrix surface. However, as the degree of orientation of the organic constituents is much less than the mineral constituents, it is postulated that the site of nucleation of the mineral crystals comprises only a small part of the matrix structure and is itself composed of well oriented macromolecules, probably acidic proteins. Two acidic proteins, which may constitute part of the nucleation site for calcite in a bivalve, were identified by comparing all the acidic proteins in the calcite layer with those in the aragonite layer. The two proteins were present in the calcite layer only, and in addition were found to have an aspartic-acid -containing amino acid sequence, not present in any of the other soluble matrix proteins. The concept of a matrix composed of a structural core coated with acidic macromolecules, some of which constitute a nucleation site, may well be applicable to other mineralized tissues.

Effects of differences in mineralization on the mechanical properties of bone

Abstract: There is a considerable variation in the mineralization of bone; normal, non-pathological compact bone has ash masses ranging from 45 to 85% by mass. This range of mineralization results in an even greater range of mechanical properties. The Young modulus of elasticity can range from 4 to 32 GPa, bending strength from 50 to 300 MPa, and the work of fracture from 200 to 7000 Jm-2. It is not possible for any one type of bone to have high values for all three properties. Very high values of mineralization produce high values of Young modulus but low values of work of fracture (which is a measure of fracture toughness). Rather low values of mineralization are associated with high values of work of fracture but low values of Young modulus and intermediate values of bending strength. The reason for the high value for the Young modulus associated with high mineralization is intuitively obvious, but has not yet been rigorously modelled. The low fracture toughness associated with high mineralization may be caused by the failure of various crack-stopping mechanisms that can act when the mineral crystals in bone have not coalesced, but which become ineffective when the volume fraction of mineral becomes too high. The adoption of different degrees of mineralization by different bones, leading to different sets of mechanical properties, is shown to be adaptive in most cases studied, but some puzzles still remain.

Recent Studies of the Mineral Phase in Bone and Its Possible Linkage to the Organic Matrix by Protein-Bound Phosphate Bonds

Abstract: The most widely accepted hypothesis to account for maturational changes in the X-ray diffraction characteristics of bone mineral has been the 'amorphous calcium phosphate theory', which postulates that an initial amorphous calcium phosphate solid phase is deposited that gradually converts to poorly crystalline hydroxyapatite. Our studies of bone mineral of different ages by X-ray radial distribution function analysis and 31P n.m.r. have conclusively demonstrated that a solid phase of amorphous calcium phosphate does not exist in bone in any significant amount. 31P n.m.r. studies have detected the presence of acid phosphate groups in a brushite-like configuration. Phosphoproteins containing O-phosphoserine and O-phosphothreonine have been isolated from bone matrix and characterized. Tissue and cell culture have established that they are synthesized in bone, most likely by the osteoblasts. Physiochemical and pathophysiological studies support the thesis that the mineral and organic phases of bone and other vertebrate mineralized tissues are linked by the phosphomonester bonds of O-phosphoserine and O-phosphothreonine, which are constituents of both the structural organic matrix and the inorganic calcium phosphate crystals.

Diatom analysis and the acidification of lakes

Abstract: Diatom microfossils preserved in lake sediments can be used to provide evidence for lake acidification. Unlike documentary methods of historical reconstruction, the sediment record is potentially useful at all sites, it is usually continuous and it can be extended backwards in time as desired. Cores can be taken with little disturbance, by freezing in situ if necessary, and sediments deposited since about 1800 A.D. can be dated using $^{210}$ Pb analysis. The strong relationship between diatom occurrence and water pH allows pH to be reconstructed with a standard error of between ca. 0.25 and 0.5 pH unit using either an index system or multiple regression analysis. Although there is evidence that long term acidification is a natural process for lakes in areas of resistant base-poor bedrock, diatom analyses from NW European and North American sites shows that rapid acidification has taken place within the last 150 years. The first major sign of acidification is the loss of planktonic diatoms at pH values between about 5.5 and 5.8. Acidification below pH 5.5 leads to the decline of species typical of circumneutral water, such as Achnanthes microcephala Kutz. Cymbella gracilis (Rabh). Cleve and Anomoeoneis vitrea (Grun). Ross, and the expansion of acidophilous taxa such as Tabellaria flocculosa (Roth.) Kutz. and Eunotia veneris (Kutz.) O. Muller. Acidobiontic species become common at pH values less than 5.5 and as the pH drops to 4.5 these taxa begin to replace acidophilous taxa in the assemblage. Tabellaria binalis (Ehr.) Grun. is probably the most faithful member of this group. Diatom analysis for four acid lakes in Galloway, SW Scotland show that the beginning of acidification has varied from 1840 (Loch Enoch) to 1925 (Loch Grannoch) and that pH has declined by between ca. 0.5 units (Loch Dee) and ca. 1.2 pH units (Loch Grannoch) in these lakes. Since lakes without afforested catchments have been acidified and lakes with afforested catchments were acidified before afforestation it can be concluded that afforestation is not responsible for acidification in this region.

The aerodynamics of hovering insect flight. v. a vortex theory

Abstract: A full derivation is presented for the vortex theory of hovering flight outlined in preliminary reports. The theory relates the lift produced by flapping wings to the induced velocity and power of the wake. Suitable forms of the momentum theory are combined with the vortex approach to reduce the mathematical complexity as much as possible. Vorticity is continuously shed from the wings in sympathy with changes in wing circulation. The vortex sheet shed during a half-stroke convects downwards with the induced velocity field, and should be approximately planar at the end of a half-stroke. Vorticity within the sheet will roll up into complicated vortex rings, but the rate of this process is unknown. The exact state of the sheet is not crucial to the theory, however, since the impulse and energy of the vortex sheet do not change as it rolls up, and the theory is derived on the assumption that the extent of roll-up is negligible. The force impulse required to generate the sheet is derived from the vorticity of the sheet, and the mean wing lift is equal to that impulse divided by the period of generation. This method of calculating the mean lift is suitable for unsteady aerodynamic lift mechanisms as well as the quasi-steady mechanism. The relation between the mean lift and the impulse of the resulting vortex sheet is used to develop a conceptual artifice - a pulsed actuator disc - that approximates closely the net effect of the complicated lift forces produced in hovering. T he disc periodically applies a pressure impulse over some defined area, and is a generalized form of the Froude actuator disc from propeller theory. The pulsed disc provides a convenient link between circulatory lift and the powerful momentum and vortex analyses of the wake. The induced velocity and power of the wake are derived in stages, starting with the simple Rankine-Froude theory for the wake produced by a Froude disc applying a uniform, continuous pressure to the air. The wake model is then improved by considering a ‘modified’ Froude disc exerting a continuous, but non-uniform pressure. This step provides a spatial correction factor for the Rankine-Froude theory, by taking into account variations in pressure and circulation over the disc area. Finally, the wake produced by a pulsed Froude disc is analysed, and a temporal correction factor is derived for the periodic application of spatially uniform pressures. Both correction factors are generally small, and can be treated as independent perturbations of the Rankine-Froude model. Thus the corrections can be added linearly to obtain the total correction for the general case of a pulsed actuator disc with spatial and temporal pressure variations. The theory is compared with Rayner’s vortex theory for hovering flight. Under identical test conditions, numerical results from the two theories agree to within 3%. Rayner presented approximations from his results to be used when applying his theory to hovering animals. These approximations are not consistent with my theory or with classical propeller theory, and reasons for the discrepancy are suggested.

Mapping of cytochrome oxidase patches and ocular dominance columns in human visual cortex

Abstract: The cytochrome oxidase stain was applied to autopsy specimens of human brain. In primary visual cortex patches of darker enzyme staining were present in layers II, III, IV b, V, and VI. The patches were oval, about 400 by 250 µm, with a density of one patch per 0.6-0.8 mm 2 of cortex. They were organized into rows spaced about 1 mm apart, intersecting the 17-18 border at right angles. The patches also stained preferentially for AChE activity. The lateral geniculate body was examined in two patients who died many years after losing one eye as adults. In atrophied laminae cytochrome oxidase activity was severely reduced. In the visual cortex from three cases after monocular enucleation, regular alternating light and dark columns of cytochrome oxidase activity were visible in layer IV c, presumably corresponding to ocular dominance columns. In two cases their pattern was reconstructed over 200-400 mm 2 of striate cortex. The columns appeared as roughly parallel slabs about 1 mm wide, oriented perpendicular to the 17-18 border as in the macaque. In the upper layers light and dark rows of patches were present, which fit in register with the light and dark ocular dominance columns below. In layer IV the ocular dominance columns were also visible in Nissl stained sections as a consequence of secondary anterograde transneuronal degeneration. Darker Nissl stained columns matched lighter cytochrome oxidase stained columns corresponding to the missing eye. Quantitative measurements demonstrated a 10% loss of mean cell area and 35% increase in cell density in ocular dominance columns belonging to the missing eye, which accounts for their darker appearance in the Nissl stain. Patches were not present in a foetus at six months gestation. However, they were clearly formed in a six month old baby, although they appeared smaller and more closely spaced than in the adult. These results show that patches are present in man, in addition to other primates, although they appear proportionately larger. Ocular dominance columns are also present, in common with certain species of primates like the macaque, baboon and galago. Cytochrome oxidase histochemistry promises to be a useful technique for mapping anatomical features of the human brain post mortem .

The effects of pressure on the molecular structure and physiological functions of cell membranes

Abstract: The effects of high pressure on the phase state and molecular structure of pure lipid bilayers are discussed. The relations of $\Delta$ H, $\Delta$ S and $\Delta$ V in phase transitions are straightforward and are discernible in heterogeneous bilayers in natural membranes. The effects of pressure on the dynamic properties of bilayer constituents are less clearly understood, but order parameters obtained at pressure by different techniques show agreement. The extent and significance of hydration is poorly understood. Four physiological functions are discussed: passive permeability, active transport, membrane excitability and synaptic transmission. It is shown that a full interpretation of the kinetic effects of pressure on these processes requires much more detailed molecular information than is available at present.

The Carboniferous Amphibian Proterogyrinus scheelei Romer, and the Early Evolution of Tetrapods

Abstract: Proterogyrinus scheelei Romer, from the Upper Mississippian of Greer, West Virginia, is one of the earliest known members of the amphibian infraorder Embolomeri. The primitive, eogyrinid-like skull conforms to Panchen's allometric plot of the British eogyrinids. It has no identifiable autapomorphies, but shares with two other, as yet undescribed genera attributed to the same family, a unique skull table with a raised pineal foramen rim and an acuminate median ridge on the skull table posteriorly, flanked on each side by a deep depression. The kinetic junction extends from the otic notch anteriorly to the posterodorsal corner of the orbit. The braincase, bearing no ossified roof, is composed of separate otic-occipital and sphenethmoid units, the latter bearing no sagittal or parasagittal septa. The vertebrae are similar to those of other embolomeres, except that the pleurocentrum retains a dorsal suture in adults, and the intercentrum, unossified dorsally in adults, is a ventral cresent. The presacral count is 32. The atlas-axis is reptiliomorph. The limbs and girdles are similar to those of Archeria, except that they are slightly stouter. Humerus structure is primitive. Range of limb movement, at least in the pectoral limb, is very restricted. The possession of few autapomorphies indicates that Proterogyrinus is a member of the stem family (Proterogyrinidae) of the infraorder Embolomeri. Although most of the putative autapomorphies of anthracosaurs that were formerly thought to preclude them from reptile ancestry are not considered to be valid, there are no undisputed synapomorphies with reptiles either, making it impossible to support close relationship between the two groups.

Sphagnum-dominated peat bog: a naturally acid ecosystem

Abstract: $Sphagnum$ -dominated peat bogs are naturally acid and cover perhaps 1% of the Earth's land surface. The temporal and spatial variations of pH in a peat-bog in the northern Pennines are used to illustrate the relative importance of different sources of acidity. At this site, where the pH of rain in summer was 4.0-4.2, rain and cation exchange of metal cations in the rain for H $^+$ in the newly grown Sphagnum were of about equal importance, though cation exchange probably dominated on hummocks in summer. Strongly acid `events' are likely to follow heavy rain that follows a dry spell. The effects of interconversion of sulphur- and nitrogen-containing compounds on acidity is obscure.

Role of Glycopeptides and Peptides in Inhibition of Crystallization of Water in Polar Fishes [and Discussion]

Abstract: In the ice-laden polar oceans, water temperatures of — 2 °C are common. This temperature is 1.1 °C below the equilibrium freezing point ( — 0.9 °C) of the fishes’ body fluids. Avoidance of freezing in these environments has been linked to the presence of unusual blood peptides and glycopeptides. These molecules have molecular masses ranging from 2.5 to 20 kDa and are viewed as having antifreeze properties because they lower the freezing point of water by a non-colligative process. A 2% solution of antifreeze has a freezing point of — 1.2 °C and ice formed in their presence melts at — 0.02 °C. Measurements of antifreeze concentrations in ice indicate that these molecules, unlike other proteins of similar size and conformation, are incorporated into the solid phase during freezing and adsorb to it. Adsorption of the antifreezes to ice appears to inhibit growth along the preferred axes ( a -axes) by raising the curvature of the growth steps on the basal plane. At temperatures below — 1.2 °C, crystal growth occurs in the form of long spicules whose axes are parallel to the c -axis, the non-preferred axis of growth.

Mechanism of calcification in the marine alga Emiliania huxleyi

Abstract: Coccoliths are delicate calcified structures produced by marine unicellular algae. In the species Emiliania huxleyi the calcium carbonate (mostly calcite) is closely associated with a complex, acidic polysaccharide which binds calcium ions specifically, interferes with the in vitro crystallization of calcium carbonate, and appears to be bound to a positively charged protein before the crystallization process is finished. Ultra-high resolution electron microscopy of the coccoliths reveals that the crystallographic structure differs in different parts of the constituent calcite elements. The synthesis of the coccoliths takes place intracellularly, and when this process is ended the coccoliths are extruded and incorporated into the so-called coccosphere surrounding the cell. Transmission electron microscope studies reveal the localization of polysaccharides in the calcifying organelle by means of cytochemical staining technique. The results are combined in a putative scheme describing coccolithogenesis.

Biosynthesis, processing and transport of storage proteins and lectins in cotyledons of developing legume seeds

Abstract: The storage proteins and lectins that accumulate in the protein bodies of developing legume cotyledons undergo a number of processing steps along the transport pathway from their site of synthesis to their site of deposition. The polypeptides are synthesized on polysomes attached to the endoplasmic reticulum. Synthesis of the polypeptides is always accompanied by the co-translational removal of a signal peptide. Those proteins that are glycoproteins in their mature form are co-translationally glycosylated with high-mannose oligosaccharide side chains. Co-translational sequestration into the lumen of the endoplasmic reticulum is followed by the formation of oligomers. Transport of these oligomers to the Golgi complex may occur via tubular connections between the endoplasmic reticulum and the Golgi. In the Golgi complex some of the high-mannose side chains are modified by the removal of five to six mannosyl residues, and the addition of fucosyl and terminal N-acetylglucosaminyl residues. This phenomenon has so far been observed only for phytohaemagglutinin, the lectin of Phaseolus vulgaris. From the Golgi complex the storage proteins and lectins are transported to the protein bodies. This transport is mediated by small electron-dense vesicles. In the protein bodies two types of processing occur: proteolytic processing resulting in the formation of smaller polypeptides, and glycolytic processing resulting in the removal of the terminal N-acetylglucosaminyl residues from the modified carbohydrate side chains. All storage proteins and lectins undergo some of these processing steps, and specific examples are discussed in this paper.

Collagen: the organic matrix of bone

Abstract: Collagen is the principal organic matrix in bone. The triple helical region of the molecule is 1014 amino acids long. In fibrils these molecules are staggered axially by integers of 234 residues or 68 nm (D). This axial shift occurs by self-assembly and can be understood in terms of a periodicity in the occurrence of apolar and polar residues in the amino acid sequence. Because the molecular length L = 4.47 D, there are gaps 1.5 X 36.5 nm regularly arrayed throughout the fibrils. The three-dimensional molecular arrangement is a quasi-hexagonal lattice with three distinct values for the principal interplanar spacings. Analysis of the intensity distribution in the medium-angle X-ray diffraction patterns from tendons has produced the following picture of the molecular arrangement in fibrils (Fraser et al. 1983). The molecular helices have a coherent length of 32 nm and are tilted parallel to a specific place within the lattice. A regular azimuthal interaction exists between these helices. This crystalline region could be the overlap region with a non-crystalline gap region. However, the gap is still regular axially and the molecular helices retain their structure; their lateral packing is perturbed although they retain a 'gap'. Neutron and X-ray scattering experiments have shown that calcium hydroxyapatite crystals occur in the gap and are nucleated at a specific though unknown location within the gap. The c-axis of the apatite crystals is parallel to the fibril axis and its length c = 0.688 nm is close to the axial periodicity in a protein with an extended beta-conformation. If the telopeptides at the end of a collagen molecule do have this conformation they would either have a highly heterogeneous conformation or exist in a folded manner because the overall length of the telopeptides is shorter than a regular collagen repeat of 0.029 nm would allow.

Effects of Acidic Deposition on Forest Soil and Vegetation

Abstract: The paper concerns the potential effects of acidic deposition on the nutrient status of soil and forest and on the possible toxic effect of increased Al solubility. The nutrient status of trees may be influenced by pollutants interacting with the foliage and also by changing availability of nutrients in the soil. N compounds are often absorbed by the canopy whereas base cations are lost to the soil by foliar leaching. Cation leaching increases with increased acidity of precipitation. Throughfall acidity varies with tree species, season and distance from the emission areas. The impact of increased foliar leaching of base cations is not well known. In soil, acid deposition may have three effects: (i) a fertilizer effect caused by the deposition of N, and possibly, under specific conditions, also of S; (ii) an acidification effect caused by increased leaching of base cations; and (iii) an Al toxicity effect in cases where soil acidity is increased. Results of fertilizer experiments indicate that the atmospheric deposition of N is likely to increase forest growth especially in the northern parts of North America and Europe. At more southerly latitudes, nutrients in addition to N are often deficient. Therefore the N deposition is less likely to stimulate forest growth. Sulphur deposition is not likely to increase forest growth in most areas of the temperate zone. On the contrary, S deposition will mostly increase leaching of base cations such as Mg $^{2+}$ and Ca $^{2+}$ , and possibly K. Experiments with artificial acidification together with observations of increased Mg-deficiency in central Europe, indicate that Mg-deficiency might become a problem on sensitive soils exposed to acid deposition. The possibility of Al toxicity caused by increased soil acidity is discussed on the basis of experiments with seedlings of Norway spruce. It is concluded that Al toxicity appears to be unlikely unless the Al concentrations in the soil solution increase to about 20 mg l $^{-1}$ .

The Role of Stable Complexes that Repress and Activate Eukaryotic Genes

Abstract: The state of activity or repression of 5S RNA genes is built into the chromatin in the form of stable complexes. The characteristics and composition of these complexes will be described. Stable transcription complexes that activate 5S RNA genes consist of multiple factors bound tightly to a control region of the gene. Repressed 5S RNA genes do not have these factors bound to them; their repressed state is maintained by nucleosomes.

Structure and Organization of the C4 Genes

Abstract: This 200000 M r serum protein is coded for by at least two separate loci, C4A and C4B , which map in the HLA Class III region on chromosome 6 in man Both loci are highly polymorphic with more than 30 alleles, including null alleles assigned to the two loci The complete nucleotide sequence of a full length C4A cDNA clone and a substantial part of a C4B cDNA clone has shown class differences which can be used to synthesize nucleotide probes specific for C4A and C4B Three C4 loci of approximately 16 kilobases each spaced by 10 kilobases have been identified in DNA from one individual and aligned 30 kilobases from the factor B gene by overlapping cloned genomic fragments from a cosmid library Characterization of these genes by restriction mapping, nucleotide sequence analysis and hybridization with C4A and C4B specific synthetic oligonucleotides show that these genes are very similar

Structure of the Variant Glycoproteins and Surface Coat of Trypanosoma Brucei

Abstract: The pathogenic African trypanosomes have a unique mechanism for antigenic variation. Each cell is covered by a surface coat consisting of about seven million essentially identical glycoprotein molecules drawn from a large repertoire of variants, each encoded by an individual gene. Amino acid sequence variation extends throughout the molecule but reduces from the amino terminus to the carboxy terminus, where certain features, especially the grouping of cysteine residues, are quite conserved. The range of diversity within the thousand or so variant glycoprotein genes that exist in each cell is large. New variants may arise instantaneously by segmental gene conversion. Variant surface glycoproteins are synthesized with amino terminal signal sequences and hydrophobic carboxy terminal tails. The tails are extraordinarily conserved. After synthesis, they are replaced by a complex glycolipid structure in which myristic (dodecanoic) acid serves to anchor the polypeptide to the surface membrane. Enzymic cleavage of myristic acid releases variant glycoproteins from the surface coat.

The Structural and Evolutionary Relationships of the Prolamin Storage Proteins of Barley, Rye and Wheat

Abstract: The major endosperm storage proteins of barley, wheat and rye are soluble in aqueous alcohols, either native or after the reduction of disulphide bonds, and can be defined as prolamins. They can be divided into three groups on the basis of their chemical characteristics, notably their molecular mass and amino acid composition, and the chromosomal location of their structural genes. Two of the groups, the high molecular mass prolamins and the sulphur-poor ( $\omega$ -gliadin-type) prolamins, show clear homology between the three species. The remaining prolamins are characterized by a high content of cysteine. In wheat this is a complex mixture of at least three groups of components that vary in their aggregation properties and N-terminal amino acid sequences. The precise chemical and genetic relationships of those components to each other and to the more clearly defined groups of sulphur-rich prolamins of rye and barley are still not completely understood.

Structure and Organization of the Nervous System in the Trochophore Larva of Spirobranchus

Abstract: The trochophore larva of the polychaete Spirobranchus polycerus is described, based on ultrastructural surveys and three dimensional reconstructions, with emphasis on the structure and organization of the nervous system. A complete and detailed description is provided of the larval parts of the nervous system at the cellular level for the 48 h stage, by which time the larval system is fully developed in most respects. The adult nervous system, whose rudiments form a largely separate system of nerves and nerve cells, appears progressively during later development. Its principal structures, the brain, commissures and ventral cords, are briefly described based on an examination of the metatrochophore. The larval nervous system is entirely presegmental and is divisible into two parts: (1) a system of pretrochal cells and nerves arising from them that innervates the prototroch, linking it to the apical organ and the single larval eye, and (2) a system of intratrochal and intraepithelial nerves supplying the feeding apparatus of the larva. The latter consists of two nerves that encircle the pharynx and join basally beneath the cluster of cells that make up the basal pharyngeal complex. The pharyngeal nerves are then linked by means of a suboral complex of four sensory cells and their nerves to the nerves supplying the metatroch and neurotroch. The two parts of the larval system are anatomically separate and develop separately, each in association with its own organizational centres. These are: the apical organ and its central plexus in the case of the pretrochal system, and the suboral and pharyngeal complexes in the case of the oral and pharyngeal nerves. Like the larva itself, the larval nervous system is specialized and highly reduced. There are comparatively few cells, but a number of distinctive cell types. At 48 h, the larval system comprises 36 cells, including among these between 16 and 18 recognizably different types of sensory and non-sensory nerve cells and non-neural accessory cells. The majority of the cells are individually identifiable by morphology, ultrastructure and location, and are invariant or nearly so from larva to larva. The development of the system as a whole involves production of fibres by certain of these followed by fibre growth either along preestablished pathways, for example along the trochal bands or cells derived from these, or towards identifiable targets, for example, the apical plexus or pharyngeal complex. The resulting system varies little from larva to larva, and neurogenesis appears therefore to be a very precisely controlled developmental process. However, the individual cellular events that occur as parts of this process, do exhibit considerable diversity, both in terms of the cell types involved and of the types of interactions that occur between them, which raises the question of how the degree of developmental precision required by Spirobranchus is achieved. Cell lineage and lineage-dependent phenomena are clearly important, but it is not clear how concepts arising from linage studies in other organisms, e.g. in nematodes or other spiralia, should be applied in dealing with this particular case. Besides being anatomically separate, the two main parts of the larval nervous system evidently also have different evolutionary origins. Comparison of the Spirobranchus trochophore with the closely related M uller’s larva of polyclads supports the idea that the pretrochal system of the former is derived secondarily from the adult nervous system of some ancestral form despite the fact that it innervates a strictly larval organ, the protrotroch. Conversely, the nerves supplying the trochophore oral apparatus, which includes secondarily-derived adult structures like the pharynx, are of larval origin, probably derived by rearrangement from the nerves of a series of primitive trochal bands. The basic features of the oral apparatus in both Muller’s larva and the trochophore can be accounted for by assuming the existence of an ancestral larva with three circumferential trochal bands. Two of these would then be incorporated into the stomodeum as it evolved, with their nerves being retained as stomodeal structures in modern forms. This interpretation emphasizes (1) the evolutionary conservatism of the larval nervous system, i.e. larval nerves change less in organization and arrangement than the structures they innervate, which makes them important phylogenetic indicators, and (2) the importance of the evolutionary continuity of the mouth in protosomes as a justification for comparative studies of the oral apparatus in spiralian larvae that seek to establish homologies between them. In the case at hand, it is concluded that the oral apparatus of M uller’s larva and the trochopore, excluding the anus of the latter, are homologous. The functional operation of the larval nervous system in Spirobranchus is discussed briefly and in general terms. The larval nerve cells show a low degree of morphological differentiation, and specialized cell junctions (e.g., synapses) are largely absent, so only a rudimentary understanding of the circuitry of the larval system is possible. Further, it is not clear to what extent the morphological and ultrastructural differences between the various larval cell types and between larval and adult nerve cells reflect significant functional and physiological differences. It would be most interesting if such differences did exist: the trochophore would then have to be accorded independent status as an organism physiologically quite different from the adult polychaete with, in particular, a far more primitive nervous system.

The chemistry of legume storage proteins

Abstract: Evidence is summarized that provides a structural description of the glycinin subunits from soybeans and the structural genes that produce them. Each subunit consists of an acidic polypeptide component that is linked to a basic one by a single disulphide bond. The subunits are initially produced as a precursor that consists of amino acids for the signal sequence, followed by the sequence for first the acidic and then the basic polypeptide. Comparison of the nucleotide sequence for a subunit gene with the complete prim ary structure of that subunit permits identification of a num ber of post-transcriptional and post-translational events that occur during expression of the gene.