HETEROMERA. - The beetles comprising this section have five joints to the first four tarsi, and four to the posterior pair, and form two groups, Trctchelia and Atrachelia.

Trachelia have the head triangular or heart-shaped, and connected with the thorax by a kind of neck or abrupt pedicle. Most of the species in the perfect state live on various plants, of which they devour the foliage or suck the juices, and many when seized bend their heads, contract their limbs, and simulate death. This group includes the Oil Beetles (ireloe) (Plate VIII. fig. 2), large black insects, destitute of wings, and with short elytra. They secrete an oily fluid possessing slightly blistering properties, which when alarmed they emit from the joints of their legs, and when eaten by cattle, as they sometimes are when feeding on the wild buttercups of pasture-lands, they produce sores in the mouth. In some parts of Spain they are used instead of the Blistering Fly, or are mixed with it. The young lame of several species of Oil Beetles, it has been ascertained, get conveyed to the nests of bees, where alone they can find their appropriate food, and where also they undergo metamorphosis. The most important insect of this group is the Spanish Fly, or Blistering Beetle (Lytta vesicatoria) (Plate VIII. fig. 19), found abundantly in South-Western Europe, but of rare occurrence in England. It is a handsome insect of a golden green colour, and measures about three-fourths of an inch in length. In Spain, where this species is most abundant, they are collected for commercial purposes in the month of June. A sheet is placed beneath the trees frequented by the blister-flies, and the branches are shaken, so as to cause the insects to fall off. They are then killed by exposure to the vapour of vinegar, and completely dried after they are dead. The blistering principle, known to chemists as cantharadin, is contained in their integuments. See CANTHARIDES, The Atrachelia have no distinct neck, the part of the head behind the eyes being immersed in the thorax. They are in most cases nocturnal insects, obscure in colour, and slow in motion. The Church-yard Beetle (Blvs mortisaga) (Plate VIII. fig. 1) is one of the commonest species. It is of a shining black colour, avoids the light, and emits an offensive odour. It is found in cellars, store-rooms, and the neglected parts of houses, feeding on rubbish of all kinds, and regarded as of evil omen by the superstitions. It is very tenacious of life, having been known to survive several hours immersion in spirits of wine, and cases are on record in which the larvm have been discharged from the human stomach. The Meal-worm is the larva of Tenebrio molitor (Plate VIII. figs. 4, 5), a well-known insect belonging to this group, which appears in the evening in the least frequented parts of houses. It is found abundantly in flour-mills and bake-houses, greatly relishing the heat of the latter. The larvze, which are long, cylindrical, and of an ochry yellow colour, pass their lives enveloped in the flour which forms their favourite food, and in the midst of which they become pup. While injurious to flour and bran, and destroying great quantities of ship biscuits, the Meal-worm is used as bait by fishermen, and as food for the nightingale and other pet insectivorous birds.