ENTOMOLOGY. This is the science which treats of the habits, transformations, and physical structure of insects; or the science or natural history, and description of insects. An insect is an articulate animal form, having the body com posed of three distinct parts, the head, corslet or thorax, and abdomen ; the legs are six in num ber with, usually, two or four wings attached to the thorax; and, along the sides of the abdomen minute punctures, called spiracles, by means of which respiration takes place. Formerly spiders, and crnstacea, and even worms and other small animals, were included under the term insect. The term is now restricted to the hexapods, or the six-footed species, known as beetles, bugs, bees, grasshoppers, locusts, fleas, etc., primarily produced from eggs, whatever secondary modes of propagation may take place. The egg state constitutes one of the most important epochs in insect life, since on this depends all the subse quent states and developments affecting devel opment and decay. From the egg the larva is. produced. The late and lamented Dr. Le Baron, has carefully and tersely described the outlines of Entomology, and insects in general, in one of his valuable reports : From it we extract : Insects as a class, and in the wide,t, meaning of the word, comprise three divisions, or sub-classes, com monly known as spiders, insects and millipedes. They may be distinguished by the following characters : 1. Sub-class : Arachnida , including spiders. scorpions and Acari, or mites. Body divided into two parts, the head and thorax being united in one ; legs eight in number : without wings. 2. Sub-class; Insecta, or insects proper. Body divided into three parts, the head, the thorax, and the abdomen ; legs six ; furnished_ with wings, in the perfect or imago state. 3. Sub-class : Myriapoda, commonly called milli pedes or centipedes. Body divided into many parts or segments, varying from ten to two hun dred; legs numerous; usually either one or two. pairs of legs to each segment of the body; never have wings. The exceptions to these characters are very few. In the Arachnids, some of the most minute (Acati) have but six legs. Insects proper are alway-s six-legged in their last or perfect state; and they also generally have six true legs in their larva state; but some larvm have no legs, and the larvw of the Lepidoptera, coin monly called caterpillars, have, in addition to their six true legs, several pairs of false legs. or
pro-legs, which assist in locomotion. There are a few exceptional cases in which insects are des titute of wings. The fleas (Pulice8), the lice (Pediculi), and the little family of insects known_ as spring-tails (Thy8anoura), never have wings In some rare instances the females are wingless, whilst the males have wings. This is the case with some species of the lightning-beetles (Lam pytidee), and with the canker-worm moth, and the tussock-moth, and a few other species amongst the Lepidoptera. Similarly exceptional cases are also found in other orders of insects. The present work tieats only of insects proper. The nervous system of insects consists of a double cord extending the length of the body, and lying upon the inferior or ventral side of the internal cavity. Tbe two threads which com• pose this cord do not lie side by side ; but one above the other. The lower thread swells at intervals into little knots of nervous matter, called ganglia. In insects of an elongated form, suet' as some of the Neuroptera, and the larvte. of the Lepidoptera, there is a ganglion at each segment of the body, making thirteen in all ; but in inost mature insects the ganglia become more or less consolidated. In the butterfly (Papilio), there are ten ganglia, counting the brain as one: in the bee (Apia), there are eight; in the may beetle (Melolontha), there are five, and in the. Cicada there are but two. The upper of the two nervous threads runs nearly in contact with the lower, but is destitute of ganglia. These two threads seem to represent the double and more compact cord which constitutes the spinal mar row of the higher or vertebrated animals. The upper simple thread is supposed to furnish the nerves of motion, and the lower and ganglionic thread, the nerves of sensation. The fibres which compose these cords separate at the anterior extremity of the body, so as to embrace the cesopbagus or gullet, above which they again.