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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.

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.

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.

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.