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The incidence of autotomy is described for a discrete population of Carcinus maenas in the Yealm Estuary over a period of one year. During this time the crabs showed seasonal trends in distribution whereby during the summer months they congregated at the top of the estuary. This seasonal migration up and down the estuary corresponded with peak rates in the rate of change in temperature of the bottom water. Recruitment occurred in June, July and August. Overall, there were more female than male crabs although the ratio varied throughout the year. All sizes and sexes of crabs autotomized limbs but although autotomy increased with the size of the crabs it showed no obvious relationship with other population parameters. Significantly more chelipeds than walking limbs were lost. There were more multiple autotomies than would be expected if autotomy was a random event. Autotomy is shown to be a rare event for sexually mature Carcinus but essential to the survival of immature crabs. The means by which crabs may regulate the incidence of autotomy is discussed.

With 13 figures in the text)The propagation of vibrations along the trunk and branches of a manuka tree, generated in response to the impact of a steel ball-bearing on the trunk, was measured with an accelerometer. The impact generated bending waves which travelled along the trunk and into the branches.Close to the point of impact the waveform was dominated by a damped oscillation at 518 Hz; as the bending wave progressed away from the point of impact the frequency of the dominant waveform increased. Beyond 200 cm the waveform became increasingly complex and a smallamplitude, high-frequency component progressively preceded the main wave. Branching points also induced complex waveforms, particularly where branches lay at a large angle to the trunk. Stndulating wetas also generated bending waves in the tree at a frequency close to that generated by the ball-bearing, as well as at a higher frequency of 7.5 kHz. The acoustic frequency of stridulation peaked at 0.8 and 3.4 kHz. Records from nerves serving the vibration-sensitive subgenual organs showed that wetas can detect oscillations at 1 kHz at 0.015ms-2. A stridulating weta placed on the same log as a preparation in which the nerve from the subgenual organ was monitored generated oscillations well above the threshold for detection.

1. The maximum force exerted against an isometric force transducer by 6 leeches weighing 2.6 3.7 g, as they squeezed through apertures of different widths varied inversely with aperture width. 2. T cells in the leech skin code for velocity of indentation, not pressure or displacement. The frequency with which T cells fire is best described by two log functions, one for low, another for fast indentations. T cells responded to indentation velocities down to 10 gm s-1. 3. The average threshold pressure for 5 P cells was 150 kPa and for 5 N cells was 521 kPa. 4. We conclude from these data that when leeches explore their mechanical environment and initiate contact with external objects, the threshold pressure for N cells is rarely crossed. Of the three classes of mechanoreceptor, T cells are the main modality through which leeches obtain contact information, though P cells may occasionally be recruited for local pressure peaks.

The lateral rectus (LR) muscle of the pigeon was directly stimulated in situ at 41 degrees C. The length tension relationships for active and passive tension were investigated to determine the optimum muscle length (Lo). Isometric responses to single and twin pulses, tetani and sinusoidal stimulation were measured. A linear relationship was found between length and active tension during stimulation. Increase in stimulation frequency produced a corresponding shift in tension with the slope of the curves remaining the same. At Lo (1.21 times resting length) the average contraction time of single twitches was 6.03 ms and the half-relaxation time was 7.77 ms. Stimulation frequencies of 200 Hz and over gave rise to a fused tetanus. Tension increased to a maximum at 200 Hz and rate of tension rise saturated at 600 Hz. The tension response to tetanic stimulation was linear over the range 70-180 Hz. Maximum tetanic tension was around 3.48 N/cm2 and the twitch:tetanus ratio was 0.164. Prolonged activation at fusion frequency showed a high fatigue resistance. Sinusoidal stimulation with pulse trains of 100-180 Hz produced a sinusoidal response over the frequency range 0.6-40 Hz, from which the gain and phase relationships were determined. The muscle response approximates a first order low pass filter, with a characteristic frequency of 11.2 Hz. There is an additional phase lag, equivalent to the response latency, of 2.89 ms. The results are compared to the contractile properties of mammalian eye and avian skeletal muscle. The frequency response of the LR is compared to that of cat soleus and gastrocnemius and to pigeon eye movement dynamics.