The electrical power demand in aircraft has shown a very marked increase in recent years consequent on the development of many new airborne electrical devices in the field of armaments, communications and the control of flight. Whereas not many years back the total demand on the largest aircraft could be supplied from a small windmill driven generator of fractional kilowatt output, designs are now in existence requiring 24 kW. generating capacity, while larger loads are projected for future types.

The power distribution problem has therefore been widely modified and the increased importance of the electrical services performed has considerably raised the status of a onetime Cinderella.

Dysphagia and aspiration pneumonia are prevalent but infrequently studied complications following severe traumatic brain injury (TBI). Aspiration pneumonia is responsible for a significant number of long-term deaths in this population, however, the reported number of deaths attributed to aspiration pneumonia may be inaccurate. This multicentre inception cohort (n = 2545) study analysed consecutive discharges from 3 metropolitan inpatient brain injury rehabilitation units from January 1990 to October 2007 following inpatient rehabilitation following primary TBI. Subject data was linked to national death registries to determine cause of death where relevant. This study aimed to (a) evaluate the prevalence of aspiration pneumonia, percutaneous endoscopic gastrostomy (PEG) insertion and dysphagia following TBI, (b) identify the number of deaths ascribed to aspiration pneumonia, and (c) characterise associated risk factors for long-term aspiration pneumonia related deaths compared to all other causes of death. In-hospital PEG insertion occurred in 18.4% of the sample, two thirds of whom remained dysphagic at discharge. In-hospital aspiration pneumonia was recorded in 3.6% of the sample. Postdischarge, people with TBI were 79 times more likely to die from aspiration pneumonia than the general population. Risks were higher for subjects discharged to a nursing home, with severe ongoing functional disability, dysphagia at discharge, in those who had experienced in-hospital aspiration pneumonia or required PEG insertion. Early identification and risk management of dysphagia and aspiration pneumonia in TBI nursing home populations may maximise these individuals' quality and length of life.

A study was carried out in a group of 91 HIV positive gay men to investigate the relationship between social support, measures of affect and health; the changing nature of support over time; and the causal direction of this relationship. Overall levels of support for this group were found to be moderately high and consistent over 6 months and were associated with greater psychological well-being. Individuals in receipt of quantitatively different levels of support were found to differ on measures of depression, stress, coping efficacy and self-esteem, while individuals in receipt of deficient levels of support were found to be more depressed. However, initial support levels were found to be the most powerful predictors of subsequent support levels. The implications of these findings are discussed.

The general morphology of the antennary and maxillary glands, which form the major renal system of adult Crustacea, has been described and reviewed by Goodrich (1945). However, studies on the fine structure are restricted mainly to the antennary glands of decapods, including Orcotiectes sp. (formerly Cambarus sp.) (Anderson & Beams, 1956; Beams, Anderson & Press, 1956), Orconectes affinis (Kümmel, 1964), Procambarus clarkii (Miyawaki & Ukeshima, 1967; Schaffner & Rodewald, 1978), Procambarus blandingi (Peterson & Loizzi, 1974), Austropotomobius pallipes pallipes (Riegel & Cook, 1975) and Uca mordax (Schmidt-Nielsen, Gertz & Davis, 1968). The maxillary gland of Artemia salina is the only excretory system of a non-decapod which has been studied in detail (Tyson, 1968, 1969a, b). Morelli & Tobolla worked independently on the antennary glands of amphipods, Gammarus sp. (cited Kümmel, 1973), but their studies were restricted to the site of filtration.

The glands which secrete the byssus in bivalve molluscs are located in the foot. Some glands discharge into a duct at the proximal end of the foot whilst others discharge into a ventral groove which runs forward from the opening of the duct for about two thirds of the length of the foot. In Mytilus edidis a stem or ‘rachis’ is formed by the gland which surrounds the duct (Brown, 1952). The secretions of this gland are formed into flat sheets or ribbons as a result of being discharged between numerous lamellae which occupy the blind end of the duct. The secretions are derived from two types of secretory cell. One produces large granules, packed with banded filaments, which are secreted into the crypts formed by the lamellae (Tamarin, 1975). The other produces smaller, cylindroid shaped granules which are secreted along the two faces of each lamella. The stem serves as a point of attachment for collagenous threads, produced in the groove (Mercer, 1952; Pujol, 1967 a, b) by the collagen gland which secretes globules displaying regular banding (Pujol, Houvenaghel & Bouillon, 1972). The proximal end of each thread is attached to the stem by means of a collagenous cuff, each one overlapping the previous one to form a concentric arrangement of cuffs around the stem. The distal ends of the threads are attached to the substratum by a holdfast.

The R, F and B cells of the hepatopancreas of Carcinus maenas are derived from undifferentiated (E) cells at the distal end of the tubules. Observations with the scanning electron microscope on freeze fractured tubules show that (a) most of the concentrically structured granules are confined to the R cells with few in F or B cells, (b) within individual R cells, granules are of similar size, and (c) the further R cells are situated from the distal end of the tubule, the greater is the mean diameter of the granules that they contain.

Biological precipitation of barite (barium sulphate) is highly unusual (Bowen, 1966, p. 129). This mineral forms statoliths in certain ciliates (Hubert et al. 1975), but the only animals in which it is known to occur in significant quantities are xenophyophores, a group of giant deep-sea protozoans placed in a separate class within the Rhizopoda (Levine et al. 1980). The importance of these previously obscure organisms at abyssal, and bathyal depths in the oceans has lately become increasingly appreciated, mainly through the work of Tendal (1972, 1973, 1975a, b, 1980a, b; Tendal & Lewis, 1978).

Within the hepatopancreas of the shrimp Penaeus semisulcatus the functional develop ment and subsequent decay of M-‘midget’ cells is described and linked with the moult cycle. During the feeding stages the frequency of M-cells increases and they each form a large dense vacuole which contains proteinaceous material. Precursors for this material are probably derived from the haemolymph as the cells have no direct contact with the lumen of the gland. During the non-feeding stages before and after ecdysis the contents of the vacuole are progressively removed, probably to the haemolymph. Finally the cells die before the animals recommence feeding.

In the North Atlantic, the tubular agglutinated foraminifer Bathysiphon major occurs at bathyal depths off the coasts of North Carolina and north-west Africa. Apart from its large size (up to almost 10 cm long), the most distinctive feature of this species is the appearance of the test wall which has a sooty black outer layer, about 20μm thick, overlying a much thicker layer, pure white in colour and consisting of sponge spicules and small quartz grains. The black layer is composed of irregularly shaped, plate-like particles, 1–25 (xm in size. The nature and composition of these particles has been studied using light and electron microscopy, x-ray microanalysis, electron diffraction analysis and infrared spectroscopy. The particles contain calcium and phosphorous and have electron diffraction patterns and infrared spectra consistent with a hydroxyapatite composition. Minor amounts of iron are probably responsible for their black colour. We believe that this represents the first report of apatite-like (phosphorite) particles occurring in the test of an agglutinated foraminifer. The particles are most likely to originate as phosphorite grains which are agglutinated by the foraminifer, although the possibility of authigenic precipitation cannot be eliminated. The function of the outer black layer is unknown.

When the free-swimming larva of the polychaete tubeworm Spirorbis spirorbis settles permanently on a suitable substratum, it forms a thin, mucous, anchoring tube, which covers only the posterior half of the body. Within 3 h the worm has built a comparatively thick, calcareous tube onto the anterior end of the initial, mucous tube, which later becomes a compressed and folded remnant (Nott, 1973). The volume of calcareous material forming the tube cannot be stored within the body of the larva before settlement and must, therefore, be taken up rapidly from sea water or ingested material.

Previous studies with the marine gastropod Littorina littorea have shown that cadmium is concentrated in the digestive gland and that cytosolic metallothionein-like proteins sequester a large proportion of the accumulated burden. In the current investigation, an electron microscope cryo-preparation method and X-ray microanalysis have revealed that some cadmium, in association with sulphur, is localised in the region of the limiting membrane of the mineralised granules which detoxify certain metals as an insoluble phosphate salt. It appears, therefore, that there could be interaction between the sulphur and phosphate systems for binding metals within the basophil cells of the digestive epithelium.

Aspects of the digestive cycle of Carcinus maenas have been studied by transmission and scanning electron microscopy, X-ray microanalysis and light microscopy. Movements of ingested material have been followed by feeding the crabs with Mytilus edulis (L.) labelled with colloidal particles of gold or thorium oxide.

The current nomenclature for cells in the hepatopancreas of decapods is based on the classification of Jacobs (1928) and Hirsch & Jacobs (1928). They described the E-(embryonic), F-(fibrillar), B-(blister-like) and R-(resorptive or absorptive) cells. More recently the M-(midget) cell has been described (Al-Mohanna, Nott & Lane, 1984).

Accounts of the structure of these cells are reviewed by Gibson & Barker (1979) and the B-cells most closely resemble those described and illustrated in this paper for the period 24 h after feeding.

Following primary settlement and metamorphosis in Myiilus edulu (L.), the original larval stem glands (S1 and S2) increase enormously in size in the plantigrade. These glands, packed with mature secretion, discharge into a multi-partitioned posterior ducted system which is transitional in form between that of the larva and the adult. The gross enlargement of the stem glands appears to be an adaptation for frequent and copious production of byssus material during the bysso-pelagic and attachment phases of early post-larval life. This interpretation is supported by the fact that the volume ratio of the stem glands to the foot declines during subsequent growth of the young mussel and that other glands take over the function of byssus stem formation in mature mussels. Enhanced dispersal of post-larvae by bysso-pelagic drifting would account for the widespread and heavy fouling of offshore platforms by the almost exclusively intertidal mussel, particularly where these structures are far distant from coastal stocks.

It has been observed previously that the digestive gland of the carnivorous gastropod mollusc, Murex trunculus, does not accumulate metals which occur in high concentration in the digestive gland of its prey, the detritus-feeding gastropod, Cerithium vulgatum. It is proposed that mechanisms of metal detoxification which operate in C. vulgatum render metals biologically unavailable to M. trunculus. In the present work, this scheme is tested by feeding tissues containing detoxified metals from a gastropod, bivalve and barnacle to carnivorous gastropods. Metals in the prey are accumulated in insoluble granules in the digestive gland of the gastropod, kidney of the bivalve and gut connective tissue of the barnacle. These tissues are fed to the carnivores and the granules pass through the entire length of the gut. They are egested as clean preparations within the faecal pellets and they still contain the metals introduced by the tissues of the prey. This transfer of detoxification between species indicates that the food chain progression of material can result in the reduction of the bioavailability of metals. The observations are recorded by scanning electron microscopy and X-ray microanalysis.

INTRODUCTION

It is apparent, in a review on the decapod hepatopancreas (Gibson & Barker, 1979) that there is some consensus of opinion that the epithelium consists of E-, R-, F- and B-cells and M-cells (Al-Mohanna, Nott & Lane, 1985). Also, it is agreed that the gland produces enzymes and absorbs, digests and stores nutrients and excretes waste material. However, the apportionment of these functions to the different cells and the descriptions of the cytological processes involved are variously explained. Thus, the activity of proteases and amylases has been demonstrated in the secretion produced by the gland but the source of these enzymes is attributed to different cells and various modes of secretion are proposed. Also, no secretion granules of the zymogen type have been seen.

There are probably two main reasons for the inconsistent interpretation of the activities of the cells. First, the different stages of the feeding and moult cycles are not taken into account and both these affect the cytology of the gland. Second, some of the functions have been deduced from observations of the fine structure without any experimental treatments to demonstrate more directly the processes involved. In the present work all the animals are taken at the same moult stage and observations are made throughout the feeding cycle. Also, aspects of the function are studied with markers which are administered in the diet and injected into the blood. The activities of hydrolytic enzymes associated with the different epithelial cells have been studied but these will be the subject of a separate publication dealing with the cytochemistry of the digestive processes.

Tissues of Littorina littorea (Mollusca: Gastropoda) were processed for electron microscopy with an aqueous fixative which included hydrogen sulphide to precipitate intracellular cadmium. The procedure retained cadmium in the cytosol, where it was below the detection limit for x-ray microanalysis, but it did not increase the retention of the metal within lysosomes and other sites of accumulation where it was detectable. Aqueous fixation caused extraction of labile elements, particularly magnesium and potassium, and this effect was increased by the use of hydrogen sulphide. Cadmium and hydrogen sulphide had disruptive effects on the fine structure of cells. It is concluded that cytological fixatives should not include hydrogen sulphide, and that cryo-fixation is required for x-ray microanalysis of intracellular elements.

The development of the planktonic veliger larva of Mytilus edulis L. culminates in a swimming crawling stage during which the foot is of considerable importance in the selection of a settlement site. This stage has been described for many other bivalves (see Bayne, 1965) and has been given the term ‘pediveliger’ by Carriker (1961). The pediveliger of Mytilus edulis is negatively phototactic and positively geotactic during velar swimming (Bayne, 1964b) and is usually confined to water layers close to the substratum. The foot may be protruded during swimming and if it comes into contact with the substratum it adheres and a period of crawling commences. During crawling the larva progresses on the ventral or posterior surface of the foot by means of ciliary and muscular action. Crawling may result in attachment by secretion of the first byssus thread or alternatively the foot is withdrawn and velar swimming is continued until the next exploratory crawling phase. Mytilus larvae attach most readily to filamentous substrates in the field (Blok & Geelen, 1958; Bayne, 1964a).

Among the marine invertebrates whose settlement behaviour is well studied, the polychaete tubeworm, Spirorbis spirorbis L. ( = borealis Daudin), the barnacle, Balanus balanoides, and the oyster, Ostrea edulis, are different in form whether in the free-swimming or adult stage, yet the settlement behaviour patterns are basically similar (Crisp, 1973). The larvae have a sequence of movements during exploration of the substratum, with each activity initiated by a hierarchy of stimuli. Given a positive set of responses to a suitable habitat, the distances moved on the substratum are limited progressively so that finally the larva investigates a very restrictred area. When the exact site for settlement is determined the larva ceases to move, attaches permanently and immediately commences metamorphosis into the adult form. However, if certain stimuli are lacking or obnoxious to the searching larva, it recommences the initial free-swimming activity, in order to reach alternative substrata.

The dynamics of an asymmetric annulus of vorticity in an incompressible, inviscid twodimensional fluid are experimentally studied using a pure electron plasma. A strict fluid analogy requires that the plasma system behave like an ideal fluid in a frictionless cylindrical container. For certain parameters the asymmetric annulus undergoes a complex evolution which is quite different from that of a symmetric annulus. During the first ‘active’, phase the symmetries grow until the annulus collapses, leaving a large vortex at the device centre. In the second, ‘passive’, phase the remainder of the annulus winds around this central vortex into an ever tighter spiral. Finally, slow shear instabilities destroy the structure of the highly evolved spiral.