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Primers for amplification of four novel, unlinked nuclear DNA loci, the first reported for the rough periwinkles of the genus Littorina, are described. Patterns of restriction site polymorphism for these loci are detailed within the rough periwinkles. RFLPs are not found to be diagnostic for any of the currently accepted species within this group, nor for any of the contentious subspecies, or forms, whose taxonomic status is uncertain. However, there are important differences in allele frequencies between these taxa and certain of these mirror differences detected in a previous study of the mitochondrial DNA. These allele frequency data are used to construct a phylogeny in which groupings of the three recognised species are obvious when either Nei's genetic distances or Reynold's distances are clustered. Contentious forms (L. neglecta, L. saxatilis ‘b’ and L. tenebrosa) do not cluster as distinct taxa, although populations of L. neglectahave important allele frequency differences from L. saxatilis.These four loci have confirmed the consensus view of Littorinaphylogeny and provided important information on population structure‐however four loci is insufficient for reaching definitive conclusions. Since analysis of nuclear DNA polymorphisms such as these is invaluable for analysis of phylogeny, population structure and phylogeography, identification of additional loci is considered imperative.

Abstract.: A 8022 base pair fragment from the mitochondrial DNA of the prosobranch gastropod Littorina saxatilis has been sequenced and shown to contain the complete genes for 12 transfer RNAs and five protein genes (CoII, ATPase 6, ATPase 8, ND1, ND6), two partial protein genes (CoI and cyt b), and two ribosomal RNAs (small and large subunits). The order of these constituent genes differs from those of other molluscan mitochondrial gene arrangements. Only a single rearrangement involving a block of protein coding genes and three tRNA translocations are necessary to produce identical gene orders between L. saxatilis and K. tunicata. However, only one gene boundary is shared between the L. saxatilis gene order and that of the pulmonate gastropod Cepaea nemoralis. This extends the observation that there is little conservation of mitochrondrial gene order amongst the Mollusca and suggests that radical mitochondrial DNA gene rearrangement has occurred on the branch leading to the pulmonates.

The distributions of the rough periwinkles L. saxatilis and L. arcana are considered in the northern half of Robin Hood's Bay, North Yorkshire, England. The relative proportions of these two species at different sites have been determined, using the criterion of the female reproductive system for their identification. The commonest shell colour morphs are grey (both species) and orange-banded (L. saxatilis). Hence information has been obtained not only on the proportion of banded animals in the total population, but on the proportion of banded L. saxatilis.

Results of a preliminary study of filterable size fractions of iron, in four rivers in the South West of England, indicate that a significant proportion (6 to 53% w/w) of sub-micron material may be recovered in a non-dialyzable, macromolecular form (>10,000 molecular weight) using ultrafiltration. Mossbauer measurements of fulvic acid peat extracts and a molecular weight fraction (<10,000 >500 molecular weight) of iron, recovered from moorland drainage, demonstrate that a wide range of molecular environments are occupied by an iron nucleus in these macromolecules.

The occurrence of dissolved iron in rivers and estuaries is reviewed with emphasis upon colloidal and macromolecular forms and the regulatory processes governing the geochemical fate of these species.

Jet-propulsion in dragonfly larvae is achieved by the rapid ejection of water from a specialised rectal chamber via the anus, at a frequency of up to 2.2 cycles/s. Movement, forward thrust and muscular activity have been recorded in restrained and free-swimming larvae. Forward thrusts of up to 1.5 g wt result from the expiratory phases of cycles lasting 0.1 to 0.4 s. Swimming velocities are in the order of 10 cm/s. The following muscles are shown to be active during expiratory phases of jetting: anterior, posterior and respiratory dorso-ventrals; primary and secondary longitudinal tergals; lateral primary longitudinal sternopleural; dorso-ventral oblique; ventral adductors of the anal appendages. The sub-intestinal muscle is active during the inspiratory phases of jetting. Activity recorded is compared with that found during normal ventilation. The larval jet-propulsive mechanism is compared with that of certain cephalopods and found to be very effective for the larva's relatively small size.

The roles of certain abdominal muscles in ventilatory behaviour are discussed and illustrated with records of muscular activity obtained mainly from free-swimming animals. The following muscles are shown to be active during normal ventilation (Vn): respiratory and anterior dorso-ventrals (RDV and ADV), longitudinal tergal (LT), diaphragm, sub-intestinal and adductors of the anal appendages (VADP). The posterior dorso-ventral, lateral primary longitudinal sterno-pleural, and dorso-ventral oblique muscles were found to be inactive duringVn. TheRDV, ADV, LT andVADP are also active during ventilatory movements other thanVn.RDV activity is shown to be more variable in the free-swimming animal than recordings from dissected and restrained preparations previously suggested. Activity in theADV duringVn shows a reciprocal relationship with that in theRDV. Postulated control elements in larval ventilation are found to parallel many described in other ventilatory systems and motor rhythms generally.

The electrophysiological responses to mechanical stimulation of the four commonly occurring types of hair sensilla on the legs of the cribellate spiderCiniflo are described. The long, straight ‘tactile’ hairs respond preferentially to depression with activity from two phasic receptor units, one of which is sensitive to higher movement velocities than the other (Fig. 3). The units innervating the large spines respond only during erection. There is a fast adapting phasic unit and a slower adapting phaso-tonic unit (Figs. 4 and 5). It is suggested that these spines may serve partly as haemocoelic pressure monitors. The delicate trichobothria respond to small movements in all directions with directional responses from three phasic units, and are the only hairs showing true, directional sensitivity (Figs. 9, 10 and 11). The curved, blunt-tipped ‘chemoreceptive’ hairs show activity from one phasic unit when the hair is deflected in any direction away from its rest position (Fig. 8). In all cases, the number of physiologically detectable cells is one less than has been shown to be present ultrastructurally. The possible significance of these observations in relation to general araneid behaviour is discussed.

The anterior and posterior proprioceptors at the tibio-metatarsal joint of the cribellate spiderCiniflo have been studied physiologically by recording from the individual receptor nerves in response to manipulation of the metatarsus. In the anterior organ (TMant) two flexion sensitive movement units, an extension sensitive position unit and a flexion sensitive position unit were identified (Figs. 2 and 3). In the posterior organ (TMpost) there are more units present, with representatives of the above categories and also some indication of an extension sensitive movement unit (Fig. 6). The results are compared with those of the corresponding receptors in crustaceans.

The curved, blunt-tipped hairs on the legs ofCiniflo have a structure characteristic of contact chemoreceptors. Using a ‘hair tip’ recording technique, it has been possible to confirm that these sensilla do respond to contact stimulation by certain chemical substances (Figs. 1 and 3). A few experiments were also performed onTegenaria (Fig. 2). So far, positive responses to some monavalent salts (Figs. 1 and 2) and hydrochloric acid (Fig. 3) have been established, involving perhaps 5 to 6 chemoreceptor units in all. However, each sensillum is known to have 19 chemoreceptor cells and thus most of the reaction spectrum of the sensillum remains unknown. The suggestion that, in contrast to insect contact chemoreceptors (which usually have only 4–7 sensory units), some of the dendrites may be very specific receptor units and are perhaps involved in the detection of contact pheromones or other equally specific substances, is discussed.

Boron neutron capture therapy (BNCT) has been advanced as a suitable alternative therapy for the treatment of glioma. BNCT involves the selective uptake of a tumour with a boron-bearing substance and subsequent irradiation with a beam of neutrons. Previous attempts with BNCT have utilized thermal neutrons, but this involves resection of the scalp prior to treatment and is only possible with superficial tumours. An alternative is to use a beam of intermediate-energy neutrons which will produce a peak in the thermal neutron fluence at depth in tissue and so enable deep-seated tumours to be treated. A neutron beam with a mean energy of ∼ 9 keV, obtained by filtering neutrons from a reactor with aluminium, argon and sulphur, has been used to explore the radiobiological advantage over thermal and 24 keV neutrons for BNCT. Irradiation of V79 and HeLa cells at various positions in a polythene phantom suggest that the beam is less cytotoxic for a given neutron fluence than the 24 keV neutron beam previously considered as an alternative to thermal neutrons for BNCT. However, optimization of boron distribution via the development of new compounds still appears to be necessary for BNCT to become a safe alternative option for the treatment of glioma.

The mechanics of the predatory strike of Heirodula membranacea (Burm.) have been studied using high speed ciné, electrophysiological and anatomical techniques. Calculations of the muscle output required to produce the strike suggest that muscle performance generally lies within the range observed elsewhere and that no specializations for prior energy storage, as are found in some other rapid insect movements, are necessary. This view is supported by simultaneous EMG and ciné studies showing no significant delay between the onset of EMG activity and the onset of stress development required by the direct action model. The apodemes of a number of forelimb muscles are found to have complex two-point suspensions; these have a significant role in determining the moment-arm/joint-angle relationships of the muscles. The parallel-fibred part of the tibial flexor muscle has a high strain rate, 17·5 s−1, at 27–30°C. This is the fastest recorded strain rate for an insect muscle, and approaches the fastest strain rates of mammalian muscles operating at 37 °C.

For the assessment of radiation risk at low doses, it is presumed that the shape of the low-dose-response curve in humans for cancer induction is linear. Epidemiological data alone are unlikely to ever have the statistical power needed to confirm this assumption. Another approach is to use oncogenic transformation in vitroas a surrogate for carcinogenesis in vivo. In mid-1990, six European laboratories initiated such an approach using C3H mouse cells. Rigid standardisation procedures were established followed by collaborative measurements of transformation down to absorbed doses of 0.25 Gy of x-radiation resulting in a total of 759 transformed foci. The results clearly support a linear dose-response relationship for cell transformation in vitrowith no evidence for a threshold dose or for an enhanced, supralinear response at doses mGy. For radiological protection this represents a large dose, and the limitations of this approach are apparent. Only by understanding the fundamental mechanisms involved in radiation carcinogenesis will further knowledge concerning the effects of low doses become available. These results will, however, help to validate new biologically based models of radiation cancer risk thus providing increased confidence in the estimation of cancer risk at low doses.

HeLa cell suspensions were irradiated at various depths of Perspex in a beam of 70 MeV p-mesons. The dose-rate in the Bragg peak varied between 40 rad hour-1and 150 rad hour-1. The cells were assayed in vitrofor loss of reproductive integrity.The results for irradiation in the peak indicated an RBE of about 2·1 when compared to the response obtained using 60Co ?-rays at comparable dose-rates. At dose-rates of 100–150 rad hour-1, the RBE peak-to-plateau was about 1·4, whilst at lower dose-rates, the RBE peak-to-plateau was about 1.

The effect of 70 MeV p-mesons was studied to determine the effectiveness of such beams against normal tissues in vivo. The end points included thymic weight loss, oocyte and bone marrow CFU-S survival and the induction of macroscopic lens opacities. The results indicate that p-mesons are not significantly more effective for these endpoints than more conventional radiation sources such as 60Co ? rays, 220 kVp X rays, and 14 MeV X rays and electrons. Nor was there any detectable difference in RBE between the peak and plateau regions of the p-meson beam. The significance of these findings is discussed in relation to the published p-meson RBE values of between 1·4 and 5·0.

Electrocardiograms (ECGs) and electromyograms (EMGs) from the dorsal musculature of the sucking stomach of tarantulas (Grammastola cala) were recorded simultaneously from unrestrained animals during ingestion. Resting heart rates averaged 33.6±1.9 beats min−1, which increased significantly to an average of 51.6±3.8 beats min−1 during ingestion. This is not significantly different from the average sucking stomach rate of 53.6±3.9 cycles min−1. Activity of the sucking stomach constrictor muscles started with a phase shift of 0.64±0.007 cycles relative to dilator activity. In some cases the stomach dilators were active almost in synchrony with heart systole (phase shift of 0.10±0.009 relative to ECG), and the constrictors were active later in the cycle, during diastole, with a phase shift of 0.71±0.007 relative to the ECG. These data suggest that, during ingestion, fluid flows in the anterior aorta and midgut are negatively coupled as the fluids traverse the pedicel. Although such coupling was observed in about half the traces, other results were obtained that showed no evidence of coupling. Possible mechanisms for coupling and the sequence of events in the pedicel during ingestion are discussed.

Monte-Carlo computer codes have been used to estimate the distribution of doses to borated and unborated tissues in head-sized phantoms when exposed to beams of 2 keV and 24 keV neutrons. For the application of such beams to boron neutron capture therapy (BNCT) these calculations show the superiority of 2 keV neutrons over 24 keV neutrons and the importance of using large-area beams. A 24 keV neutron beam has been used to irradiate HeLa cell cultures in vitro, with and without the addition of 10B, at various depths within a narrow polyethylene phantom. Survival data obtained from these experiments have been used to estimate depth-damage profiles for normal (unboronated) and tumour (boronated) brain tissues when exposed to 24 keV neutrons. A good differential between damage to normal and tumorous tissue is obtained under suitable irradiation conditions. Although lower–energy neutrons are probably preferable, these results demonstrate the possibility of using beams of 24 keV neutrons for the BNCT of brain tumours.

HeLa human carcinoma cells and V79 Chinese hamster fibroblasts have been irradiated in vitrowith a beam of neutrons with a nearly pure 24 keV spectrum. The relative biological effectiveness (RBE) of the filtered neutron beam relative to 60Co γ radiation was determined by irradiation of cell cultures “free-in-air”. The values obtained for the RBE at 37% survival were 5.8 ± 0.8, at a dose of 0.69 ± 0.06 Gy for the HeLa cells and 3.14±1.1 at a dose of 1.09 ± 0.091 Gy for the V79 cells. Cytogenetic analysis of the damage in irradiated V79 cells gave an RBE of 6.7±1.4. Irradiation in a polyethylene phantom markedly attenuated the beam's biological effect. For both cell lines 2 cm of polyethylene virtually eliminated cell killing. Addition of boron 10 to the medium led to increased cell killing and a value of 4 was obtained for the RBE of the 10B(n, α)7Li reaction in HeLa cells.

This paper reviews the development of boron neutron capture therapy (BNCT) and describes the design and dosimetry of an intermediate energy neutron beam, developed at the Harwell Laboratory, principally for BNCT research. Boron neutron capture therapy is a technique for the treatment of gliomas (a fatal form of brain tumour). The technique involves preferentially attaching 10B atoms to tumour cells and irradiating them with thermal neutrons. The thermal neutron capture products of 10B are short range and highly damaging, so they kill the tumour cells, but healthy tissue is relatively undamaged. Early trials required extensive neurosurgery to expose the tumour to the thermal neutrons used and were unsuccessful. It is thought that intermediate-energy neutrons will overcome many of the problems encountered in the early trials, because they have greater penetration prior to thermalization, so that surgery will not be required. An intermediate-energy neutron beam has been developed at the Harwell Laboratory for research into BNCT. Neutrons from the core of a high-flux nuclear reactor are filtered with a combination of iron, aluminium and sulphur. Dosimetry measurements have been made to determine the neutron and gamma-ray characteristics of this beam, and to monitor them throughout the four cycles used for BNCT research. The beam is of high intensity (∼2×l07neutrons cm−2s−1, equivalent to a neutron kerma rate in water of 205mGyh−1) and nearly monoenergetic (93% of the neutrons have energies ∼24keV, corresponding to 79% of the neutron kerma rate).

Shell shape in gastropods is generated by the spiral path of shell material laid down at the aperture. Many aspects of shape will therefore be associated. Such associations may indicate constraints, limiting the range of variation seen in populations as a response to different environmental pressures. Associations of shell variables were studied using the sibling species Littorina saxatilis and Littorina arcana. The same closely associated subset of three variables was found in both species, related to the maintenance of a constant aperture shape, despite variation in overall morphology. These closely associated variables describe similar variation in the two species. The less closely associated variables may contribute more to inter-specific differences.

The status of the four currently recognised species in the Littorina saxatilis species-complex, i.e. Littorina nigrolineata Gray, L. arcana Hannaford Ellis, L. saxatilis (Olivi) and L. neglecta Bean is reviewed briefly, with notes on their characteristic features and location on the shore. Since the taxonomy of these rough periwinkles has only become stable relatively recently much of the previously published information on distribution is of little or no use. In this paper their distribution around the coastline of England and Wales (with some notes on Scotland) is described and discussed. L. saxatilis is found in a wide range of habitats from exposed peninsulas to estuaries on all shores where there is a suitable rocky or stony substrate; also in salt marsh pools. L. arcana has a more restricted distribution and is notably absent along much of the south English coast, central Cardigan Bay and possibly northern Scotland; it is not found in estuaries. L. nigrolineata has an even more restricted distribution, although it occurs both on exposed coasts and in estuaries; it has only been found by us in one locality on the east coast. L. neglecta is probably fairly widely distributed but we have few details so far. The implications of the different patterns of distribution are discussed.

Rough periwinkles are notoriously variable in shell characters. There are many reports of substantial local variation on single shores which not only make identification difficult but also may be difficult to understand in terms of likely selective pressures. We show that despite local variation in southern Britain there is evidence of a broader scale of change which is likely to be explicable in adaptive terms. At the same time, along an extreme environmental gradient on a single shore in south Wales we show that there are changes in morphology which are related to avoidance of water loss.

Transformation is a complex multistage process in vitro by which benign cells gradually acquire characteristics of tumour cells. Transformed C3H10T1/2 cells appear in vitro as multilayers of cells termed foci. A variety of transformed phenotypes are observed in vitro and in this study samples of these phenotypes were developed as cell lines and assessed for their ability to induce tumours in C3H mice. It was found that, while a high proportion of X-ray-induced transformants were tumorigenic, most of the alpha-particle-induced transformants were non-tumorigenic. Although tumours produced by the X-ray-induced transformants appeared earlier, they grew at similar rates to the alpha-particle-induced equivalent. Foci were classified as fully or partially tumorigenic depending on whether the foci produced at least one tumour in the mice injected (partially tumorigenic) or produced tumours in all mice injected (fully tumorigenic). It was found that tumours from the partially tumorigenic foci grew slower or appeared later than those of the fully tumorigenic foci. It is hypothesized that the apparent low tumorigenicity of positively transformed alpha-particle-induced foci is due to an increase in genomic instability of progeny focus cells compared with X-ray-induced foci leading to a larger non-viable population of cells in the alpha-particle-induced foci.

The mechanical arrangement of the PD organ of Cancer has been studied and equations derived which relate its length to the articulation angle of the PD joint and to the angle which the receptor strand makes with the dactylopodite flexor tendon. These relationships are discussed in the light of the anatomy of the PD articulation.

Radiation-induced life-shortening in Drosophila melanogaster has been measured. Flies were irradiated at a dose-rate of 1430 rads/sec whilst breathing various mixtures of oxygen and nitrogen. Neither a detectable age dependence nor a sex difference was noted. There was no difference in sensitivity with oxygen contents of 6-21 per cent; under 100 per cent nitrogen, life-shortening was reduced. This difference in sensitivity was due to an increase in the plateau region at low doses for nitrogen. For higher doses inactivation constants for both sets of curves were similar Thus the o.e.r. was dependent on the level of damage. For the acute effects of radiation there was no protection under nitrogen. This study is relevant to the effects of radiation on post-mitotic normal tissue.

Rhythmic bursts of motor activity associated with the expiratory phase of ventilation have been recorded from the second lateral segmental nerves of posterior abdominal ganglia in Aeshna and Anax larvae. In Aeshna the rhythmic expiratory bursts contain one, or sometimes two, motor units; whereas in Anax there are almost invariably three units. In both animals only one unit is associated with action potentials in the respiratory dorso-ventral muscle. Motor activity synchronized with the expiratory bursts in the second nerves has been recorded from the other lateral nerves and from the last unpaired nerve. In addition the fifth lateral nerves carry inspiratory bursts. It has been confirmed that stimulation of a first segmental nerve can re-set the ventilatory rhythm by initiating an expiratory burst in the second nerves. The original frequency is immediately resumed on cessation of stimulation. The nature of the ventilatory control system in dragonfly larvae is discussed in relation to other rhythmic systems in the arthropods.

The fine structure of the body wall muscle of the pentastomid Reighardia sternae is described. The muscle fibres are separated from one another and form two layers, circular and longitudinal. They are cross-striated with approximately 11 actin filaments surrounding each myosin filament. The T-system consists of simple in-pushings of the sarcolemma. The SR is also simple and forms both dyadic and triadic contacts with the T-system tubules and dyadic contacts with the sarcolemma. Electron-dense inclusions occur, usually in the vicinity of the Z-lines, and it is suggested that these may be composed of unsaturated lipids.

Obliquely striated muscle fibres from the longitudinal and circular layers of the body wall of the earthworm were prepared in extended and contracted states for study in the electron microscope. Contracted fibres differ from extended ones in the following respects: (i) the I-bands are narrower, (ii) the A-bands are wider, and (iii) there are more rows of thick myofilaments in each A-band. The arrangement of the thick and thin myofilaments in interdigitating arrays and the occurrence of cross-links between the 2 types of myofilament indicate a classical sliding-filament mechanism of contraction as in cross-striated muscle, resulting in a reduction in the I-band width. The increase in the A-band width could be due to a moving apart of the myofilaments during contraction to preserve constant volume of the lattice. The third change, the increase in the number of rows of thick myofilaments in the A-band, can be explained only by a shearing of these filaments past one another in such a way as to increase the amount of their overlap. The role of the sliding-filament and shearing contraction mechanisms in bringing about the changes observed in earthworm muscle fibres is considered and the possible correlation of these mechanisms with certain physiological data is discussed. The function of the sarcoplasmic reticulum in the transmission of impulses to the interior of the fibre and/or in the control of the contraction mechanism is also discussed.

Ventilatory movements of the sterna are effected by the paired segmental respiratory dorso-ventral muscles in abdominal segments 4-9 (expiration) and by the natural elasticity of the cuticle aided by two transverse abdominal muscles, the diaphragm and the sub-intestinal transverse muscle (inspiration). The former are innervated by the second segmental nerves, the latter by median nerves. Rhythmic motor discharges were recorded in the nerves to both expiratory and inspiratory muscles. Expiratory bursts consist of a single unit, the firing frequency of which increases during the burst and then normally decreases slightly at the end of the burst. Inspiratory bursts show a rather irregular discharge of the unit(s) within them, the overall frequency of which increases slightly during the first half of the burst. Each spike in the expiratory burst is accompanied by a muscle action potential in the respiratory dorso-ventral muscle it innervates. With increase in frequency of the motor unit facilitation of the muscle action potentials occurs. No such facilitation has been observed in the inspiratory muscles. The mean firing frequency of the expiratory unit increases steadily with increase in burst duration over the normal range of respiratory frequency and a similar minimum interval is attained irrespective of the duration of the burst. Expiratory bursts in second roots of the same ganglion are synchronous and may show a 1:1 relationship. Expiratory bursts start first in posterior segments and the eighth ganglion presumably contains a pacemaker. The duration and number of impulses per burst decrease from behind forwards. However, the expiratory unit reaches its maximum frequency at about the same time in all segments. Stimulation of a first segmental nerve root in the posterior region of the abdomen in an inter-expiratory period causes expiratory bursts to appear in the second roots and consequently re-sets the respiratory rhythm. The inspiratory neurones start to fire very shortly after cessation of the expiratory burst and are closely coupled with the latter. Rhythmic bursts containing many units were recorded in the isolated ventral nerve cord, usually after application of carbon dioxide to the preparation.

A study has been made of the patterns of ventilation in three genera of anisopteran dragonfly larvae by recording simultaneously the pressure changes in the branchial chamber and the dorso-ventral movements of the abdomen. The three main types of ventilation described by Tonner have been confirmed and the characteristic pressure changes during normal, gulping, and chewing ventilation are described. During normal ventilation there is a positive pressure phase of about 4 cm. water followed by a brief negative phase of 12 cm. water. The main expiratory phase is produced by the respiratory dorso-ventral muscles which are found in abdominal segments 4–9. Inspiration, which closely follows expiration, results from the elastic properties of the exoskeleton together with the activity of the two transverse muscles. One of these, lying at the anterior end of the fifth abdominal segment, forms the so-called diaphragm and divides the abdomen into two functional cavities. Gulping ventilation is characterized by a maintained pressure of 20–40 cm. water during which there may be fluctuations associated with the chewing movements, which are mainly due to the intrinsic musculature of the colon and rectum. Despite some differences in detail the main patterns of ventilation are very similar in Aeshna, Anax and Libellula.

The expiratory role of the segmental, respiratory dorso-ventral muscles, and the inspiratory role of the subintestinal muscle, have been confirmed using intact preparations of aeshnid dragonfly larvae. The strain developed by individual respiratory dorso-ventral muscles has been measured. The respiratory dorso-ventral muscles all cease firing simultaneously, about 100 msec before the sterna are fully raised, and do not have any mechanical effect on the sterna after this time. It is suggested that the delay is caused either because the role of these muscles is to lift the sterna past some critical position, and/or because of the inertia of the expiratory current. Periodically the sterna are raised and then lowered slowly in a series of steps, each pause in the lowering coinciding with activity in the respiratory dorso-ventral muscles. This form of ventilation is compared with others previously described. In normal ventilation, and in other types of ventilation, activity in the respiratory dorso-ventral muscles shows a pronounced tendency to begin in the most posterior segments and to continue for longer periods in those segments. Some aspects of the central neural connexions involved in normal ventilation are discussed.

Anal valve movement and abdominal sternal movement were photographed with a ciné camera during normal ventilation to obtain a correlation between the two parameters. As the sterna are raised (expiration) the anal valve opens to about one third of its maximum. At peak sternal movement the anal valve opens fully and these events mark the transition between expiration and inspiration. The anal valve finally closes towards the end of inspiration. The narrow aperture of the anal valve during expiration, coupled with the increase in pressure in the branchial chamber, causes the expired water to be forced well clear of the anus. Conversely, the wide aperture during inspiration and the small negative pressure in the branchial chamber ensure that water is drawn in from close to the animal, and so there is minimal mixing of expired water with inspired. The relationships between water flow, anal valve movement, branchial chamber pressure, sternal movement, pleural strain, and activity in certain expiratory and inspiratory muscles are discussed.

The PD organs of various decapod crustaceans were stimulated by elongation and relaxation of the strand, and single-unit recordings were made from the different types of sensory unit. The sensory units can all be placed in one or other of three categories : unidirectional movement cells, position cells and intermediate cells. Unidirectional movement cells are large, phasic units which respond either to elongation or relaxation of the strand. Some are pure movement-sensitive units, which reach saturation at very low movement velocities and fire over most or all of the range of movement. Other units show velocity sensitivity and differential range sensitivity in varying degrees. Position cells are small tonic units and are usually maximally sensitive at one end of the range of movement. Their firing pattern is asymmetric in that the frequency of impulses is dependent on the direction of movement by which a given position is achieved. Intermediate cells have large phasic and tonic components which may or may not show a direct relationship to each other. The importance of the detailed information produced by the PD organ is discussed and suggestions made as to how it could be utilized by the central nervous system.

The fine structure of the neuromuscular junctions in the body wall muscles of the earthworm 13 described. The segmental nerves send branches into the muscle layers. Axons in the nerve branches contain numerous synaptic vesicles and contact is established between these axons and muscle fibres or muscle tails; the latter may extend for a considerable distance from the muscle fibre. The cleft between the axolemma and sarcolemma is 85–120 nm wide and contains basement membrane material. At intervals small aggregations of electron-dense material are attached to the axonal membrane and synaptic vesicles are associated with these. The sarcolemma bears rather larger masses of dense material and is also specialized extracellularly.

The fine structure of obliquely striated muscle fibres from the body wall of the earthworm has been investigated. Certain details of the structure have been confirmed by cutting serial sections. The fibres contain both thick and thin myofilaments. The latter are attached to Z matenal and the 2 types of myofilament are arranged in interdigitating arrays to give rise to A- and I-bands and an H-zone similar to those in cross-striated muscle. The A-bands contain both thick and thin myofilaments and the I-bands only thin myofilaments. The Z-matenal is rod-shaped and these Z-rods, oriented perpendicular to the sarcolemma, are arranged in numerous parallel rows which run obliquely along the length of the fibre A line drawn parallel to the longitudinal fibre axis through a Z-rod in one row passes through a Z-rod in the next row. A thin, sheet-like array of myofilaments lies between 2 such Z-rods, forming a single sarcomere containing an A-band and 2 I-bands. The flat surfaces of neigh bouring sarcomeres are directly apposed to one another but, since the rows of Z-rods run diagonally along the length of the fibre, each sarcomere is displaced longitudinally with respect to the next, so that the A- and I-bands follow an oblique course, instead of a transverse course as in cross-striated muscle. Because of the regular stagger of the sarcomeres A- and I-bands are cut alternately in transverse sections. Also the sarcomeres are very narrow and are seen as bands lying perpendicular to the sarcolemma. In the A-band a variable number of thin myofilaments (up to 12) surrounds each thick one. Cross-links have been seen between the 2 types of filaments. In longitudinal sections an appearance similar to that seen in cross-striated muscle is obtained in one plane (perpendicular to the sarcolemma). In the plane at right angles to this (parallel to the sarcolemma) the A- and I-bands are at an acute angle to the longitudinal fibre axis. The thick myofilaments exhibit a banding of about 15 nm. There is a system of transversely oriented tubules and peripheral vesicles with dyad-like structures occurring at the juxtaposition between the peripheral vesicles and the sarcolemma. It is concluded that this system is sarcoplasmic reticulum, and it is compared with tubular systems in other muscles. Other cellular constituents are described, including a peripheral skeleton of fibrillar bundles.

HeLa cells have been irradiated in a beam of p--mesons using fractionated exposures. The response-time curve for cells irradiated in the peak and in the plateau regions showed evidence of recovery. For cells irradiated in the post-peak position recovery was either absent or delayed.

DURING the past few years a great deal of work has been done on the physiology of crustacean limb proprioceptors. The study reported here involved ultrastructural differences between functionally distinct cells in the propodite–dactylopodite (PD) chordotonal organ of Cancer pagurus, and was based on serial transverse sections. Final details will be published elsewhere.

Fracture of a left atrial catheter made of polyethylene and its subsequent embolization and entrapment in a Bjork-Shiley aortic valvular prosthesis is reported in a 62-year-old woman. The entrapped fragment of the catheter was retrieved by a transarterial approach using a homemade modified snare-loop device. Measures to prevent such a complication should be directed towards avoidance of force when removing such catheters. In addition, their length should be determined prior to insertion and again after removal, in order to detect their possible fracture and loss at once.

THE sera of the guinea pig1,2, rat3, rabbit3and man4contain the inactive precursor (pro-PF) of a globulin permeability factor (PF) activable by dilution in saline (PF/Dil) or by chemical fractionation. The in vivomechanism of activation is unknown; but an obvious hypothesis—that activation in injury is induced by contact of the pro-PFwith damaged tissue—was investigated by testing the effect on guinea pig serum of debris from homogenates of guinea pig tissues.