Attention is drawn to the widespread occurrence ofprotean phenomena, in which the appearance and behaviour of prey animals are rendered variable and irregular, as a weapon in the biological arms race between predators and their prey. Protean behaviour is defined as that behaviour which is sufficiently unsystematic to prevent a reactor predicting in detail the position or actions of the actor.Single prey animals frequently flee from a predator in an irregular manner, zigzagging, spinning, looping, or bouncing. Thissingle erratic display occurs widely in the Animal Kingdom, and may also be utilised in everyday movements of potential prey as insurance against possible attack. Examples are given.In a group of prey animals the protean aspect of escape is enhanced by the effect of numbers. In scatter reactions the effect is of multiple choice and of the simultaneous operation of several single erratics. In mobbing displays there are also successive changes in the actors' behavioural role. In protean deterrence the shuffling of individuals within a tightly packed group prevents a predator from singling one out for attack.In many species the confusing effect of changes in movement and behavioural role is enhanced by rapid changes in appearance, particularly colour.It is suggested that those prey individuals which employ escape patterns unfamiliar to the predator will tend to be at a selective advantage. During phylogeny this is likely to lead to intra-specific and inter-specific increase in the number and diversity of escape behaviours. Apostatic polymorphism is seen as a special case of protean variation within populations.There is evidence that protean displays operate by arousing neurological conflict, thereby delaying the predator's reactions and reducing the effectiveness of predatory mechanisms. Also they insure against learned countermeasures by incorporating irregularities as a basic principle. It is stressed that the irregular variability of protean displays is not accidental but has been selected for in phylogeny. A number of poorly understood behavioural aspects of the ecology of predator-prey relationships are thus united in a single theory.

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Prey animals in many different taxonomic groups behave erratically when attacked by predators. This reaction is not accidental, but acts as a specific antipredator device. Observational data and theoretical considerations indicate that such protean displays function to confuse and disorient the predator and to increase its reaction time. Thus the survival of the prey is assisted, and the selective advntage whereby such erratic patterns of the prey animals may have evolved is created.

Field and laboratory observations on the nature and sequence of the host-finding responses of the hen flea Ceratophyllus gallinae are described. The imago over-winters within the cocoon. Tactile stimuli and a rise in temperature initiate emergence. Emigration from the nest is delayed for a few days by a negatively phototactic response, and begins when this becomes positive. The fleas are negatively geotactic and disperse upwards into the vegetation. Eventually they take up a characteristic posture, oriented towards the light. Jumping is elicited when the light intensity is suddenly reduced, and it is suggested that this enables the fleas to reach their avian host. Those fleas whose jump misses the host fall and form a secondary distribution on the ground. The readiness to jump rises during the first few days after cocoon emergence, then falls again, the rate of fall apparently being partly determined by water loss.The author is much indebted to the Hon. Miriam Rothschild and Drs E. T. Burtt and M. J. Cotton for valuable advice, and to C. R. Brannigan for a critical discussion of the manuscript. The main part of the research was carried out during tenure of a post-graduate studentship provided by the Department of Scientific and Industrial Research.

The clinical features of 10 cases of lateral trunk muscle injury in first class cricket pace bowlers are described. Typically the injury occurs during a single delivery, is associated with considerable pain, and prevents the bowler from continuing. The clinical picture is typical of a muscular or musculotendinous injury. The most consistent clinical tests were focal tenderness on palpation and pain with resisted side flexion towards the painful side. The magnetic resonance image in 70% of cases was consistent with an injury to the internal oblique, the external oblique, or the transversalis muscles at or near their attachments to one or more of the lowest four ribs. The injury occurs on the non-bowling arm side. Recovery can be prolonged. The injury was a recurrence in six of the 10 cases. The biomechanics of the injury are not yet understood.