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.

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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.