A preliminary account is given of the jump of the click beetle, Athous haemorrhoidalis (F.). The jump is normally made from an inverted position. It involves a jack‐knifing movement whereby a prosternal peg is slid very rapidly down a smooth track into a mesosternal pit. The muscles which produce this movement are allowed to build up tension by a friction hold on the dorsal side of the peg. The anatomy of this jumping mechanism is briefly described. Ciné recording showed that the jump was usually nearly vertical and could exceed 0.3m in height; the beetle normally rotated several times head over tail during a jump. The jump was produced by a very rapid upwards movement of the beetle's centre of gravity during the jack‐knifing action. In a typical jump, a 4 × 10−5 kg beetle could be subjected to an upwards acceleration of 3800 m/s−2 (380 g). The minimum work done and the power output of the muscles causing jumping have been calculated. A simple mechanical model has been constructed to simulate a jump, and several possible ways in which the jumping mechanism could operate have been discussed.

No abstract

Some aspects of the energetics and mechanics of two jumps made by a single specimen of Athous haemorrhoidalis (Fab.) are considered. In the first jump, the 40 mg beetle had a take‐off velocity of 2–4 m/s and the jumping action occurred in about 064 ms; in the second jump, the take/off velocity was 2–26 m/s and the jumping action took about 0–53 ms. Energy budgets have been constructed in two different ways for each jump, and the total energy involved in each case was estimated to lie between 1–6 × 10−4 J and 3–8 × 10−4 J. Power output during the jumping action (a “catapult”) lay between 80 × 103 W/kg muscle and 180 × 103 W/kg muscle, whilst power output during the energy storing pre‐jump period (of about 0–4 s) was at least 130 W/kg muscle (at over 25°C). Forces and tensile stresses in the jumping muscles and their apodemes have also been calculated. The method of jumping appears to be fairly inefficient in that only about 50–60% of the energy expended in the jumping action is energy of translation, which actually raises the beetle.

The structure of the mouthparts and foregut of some caraboid beetles has been correlated with their type of feeding mechanism. These may be adapted to fragmentary feeding, fluid feeding (where pre‐oral digestion is important), or to mixed feeding (a large category which ranges from a mainly fluid to a mainly solid intake). Head structures concerned with feeding have been discussed in relation to these methods; they include the mandibles, maxillae, labrum‐epipharynx and anterior foregut, proventriculus, labium‐hypopharynx and the head floor. Different types of head floor were denned in relation to gular structure, in particular the presence or absence of the mid‐gular apodeme. Convergent evolution of feeding mechanisms was noted amongst both fragmentary feeders and fluid feeders; in the latter group, sucking pumps have been evolved in the Carabitae, Scarites, Cicindelidae, Paussini and some other caraboids. It was suggested that head shape in caraboids may reflect locomotory adaptations more frequently than feeding adaptations.

With 21 figures in the text)This study considers leg structure and function in the Adephaga (Caraboidea). Many ground beetles are known to be rapid runners but does this habit account for all the characteristic features of their leg structure? To answer this question, the gaits of several terrestrial Adephagan and Polyphagan beetles have been described briefly; it was concluded that they are fundamentally similar. Thus the peculiar hind legs of Adephaga (with their greatly restricted coxal angle of swing) are not specifically suited to a running habit, but are adapted for pushing. Four basic modifications for pushing have been described in the foreleg of Carabus problematicus. The particular type of pushing was apparent when the functions of its hind leg were considered. The enlarged metatrochanter contains a strong femoral rotator muscle which forces the hind tarsus vertically downwards (and the hindbody upwards). This movement is a necessary part of wedge-pushing, where the wedge-shaped head and prothorax are pushed forwards and the hindbody-the back of the wedge-is oscillated vertically to enlarge the horizontal crevice. The slightly movable metacoxa is part of the antagonistic mechanism of femoral counter-rotation, in which an ingenious lever action swings up the hind legs (and so depresses the hindbody).The most profound locomotory changes in the Adephaga reflect swimming adaptat ions. These have involved changes in the pro-and mesocoxal articulations, and the immobilization of the metacoxae. Trachypachus is particularly interesting, as it is a terrestrial Caraboid with immobilized metacoxae. The terrestrial Adephaga (mainly Carabidae) can be divided into two basic groups with divergent habits (if specialist burrowers, etc. are excluded). These groups (which merge) are the strong wedge-pushers/poorer runners with relatively large metatrochanters, and the fast runners/poorer wedge-pushers with smaller trochanters. Experimental evidence for this separation includes estimates of running speeds and the vertical forces exerted by the hind legs of several species during wedge-pushing.

SynopsisNebria brevicollis(F.) andPhilonthus decorus(Grav.) are two of the commonest predaceous insects of the woodland floor, and the head structure, mouthparts and feeding methods of each have been compared and contrasted. InN. brevicollis, the mandibles are well developed for the capture and shearing of the prey, whilst the laciniæ of the maxillæ form rakes which pull the food towards the cibarium across the smooth labium. Food is bolted in large pieces and stored in the crop before passing through the filtering and grinding gizzard. A fundamental difference between the two beetles is seen in the movements and structure of the maxillæ, and a mechanism whereby stipital abduction and protraction is effected inN. brevicollishas been proposed. InP. decorus, the mandibles are also developed for prey capture but hold the prey between large brushes while it is being crushed. The maxillæ form thick brushes which also hold the prey, and the labium-hypopharynx is densely covered with setæ which prevent the entry of solid food into the mouth. Thus, in contrast toN. brevicollis, the labrum has a median food groove which directs the food upwards and away from the mouth, and returns it to the mandibles to be re-chewed. Here, partial external digestion occurs and fluid food is sucked in by the powerful cibarial pump, and passed to the filtering proventriculus. In order to show how the two feeding methods described fit into the general pattern, the feeding methods of various predaceous Coleoptera have been reviewed in relation to different types of gut structure.

Twisted magnetic flux ropes are ubiquitous in laboratory and astrophysical plasmas, and the merging of such flux ropes through magnetic reconnection is an important mechanism for restructuring magnetic fields and releasing free magnetic energy. The merging-compression scenario is one possible start-up scheme for spherical tokamaks, which has been used on the Mega Amp Spherical Tokamak (MAST). Two currentcarrying plasma rings or flux ropes approach each due to mutual attraction, forming a current sheet and subsequently merge through magnetic reconnection into a single plasma torus, with substantial plasma heating. Two dimensional resistive and Hall MHD simulations of this process are reported. A model of the merging based on helicityconserving relaxation to a minimum energy state is also presented, extending previous work to tight-aspect-ratio toroidal geometry. This model leads to a prediction of the final state of the merging, in good agreement with simulations and experiment, as well as the average temperature rise. A relaxation model of reconnection between two or more flux ropes in the solar corona is also described, allowing for different senses of twist, and the implications for heating of the solar corona are discussed.

New results from MAST are presented that focus on validating models in order to extrapolate to future devices. Measurements during start-up experiments have shown how the bulk ion temperature rise scales with the square of the reconnecting field. During the current ramp up models are not able to correctly predict the current diffusion. Experiments have been performed looking at edge and core turbulence. At the edge detailed studies have revealed how filament characteristic are responsible for determining the near and far SOL density profiles. In the core the intrinsic rotation and electron scale turbulence have been measured. The role that the fast ion gradient has on redistributing fast ions through fishbone modes has led to a redesign of the neutral beam injector on MAST Upgrade. In H-mode the turbulence at the pedestal top has been shown to be consistent with being due to electron temperature gradient modes. A reconnection process appears to occur during ELMs and the number of filaments released determines the power profile at the divertor. Resonant magnetic perturbations can mitigate ELMs provided the edge peeling response is maximised and the core kink response minimised. The mitigation of intrinsic error fields with toroidal mode number n>1 has been shown to be important for plasma performance.