INTRODUCTION.

THE articulate branch of the animal kingdom contains animals composed of simple rings, more or less similar to each other, which contain and support the organs necessary to animal life.

According to the method in which this plan of structure is exemplified, articulate animals are divided into three classes :Body permeated by air vessels.

Body without air vessels;

INSECTA.

Thoracic region distinct from abdominal.

Thoracic region not distinct.

CRUSTACEA.

VERMES.

The class Insecta are again divided by subordinate modifications in the plan of structure into three sub-classes :—

Head, thorax and abdomen distinct, legs 6.
Head and thorax usually agglutinated, legs 8.

Head distinct, legs numerous.

INSECTA. ARACHNIDA.

MYRIAPODA.

The first sub-class Insecta (genuina) alone occupy our attention at present.

In examining the transformations of those which pass from a larval form, which is very different from the adult, we find that the changes may be grouped as follows:

1. Greater concentration of the central organs, and diminution of the number of external segments.

2. Greater complication of the peripheral organs.

3. Hardening of the integument.

We also find that certain forms, when hatched from the egg, resemble in appearance the parent, and finally assume the characters of the adult after growth, and repeated changes of skin. In others the individual emerging from the egg bears no resemblance to the adult, but after growth, accompanied with several changes of skin, passes into a condition in which a body similar to that of

the perfect insect is covered by an integument, which is finally shed. This condition is called the pupa, during which the animal is sometimes active, and sometimes inactive. The three thoracic segments are in the perfect insect either similar (except that the middle and posterior ones bear the wings) or agglutinated, or the anterior one, or prothorax, is freely movable, and the other two closely connected with each other and with the abdomen. The parts of the mouth are also modified in form, so that the mandibles and maxillæ are either free moving lateral organs fitted for mastication and prehension, or are elongated, forming a sucking tube. In the former case the mouth is said to be mandibulate, in the latter haustellate. The wings are also of various structure.

The embryological studies of insects are as yet not sufficiently progressed to enable us to subordinate these complications of structure, in such manner as to determine which forms are higher and which lower. We can merely state in general terms that those having a perfect metamorphosis are the highest; and those having the thoracic segments agglutinated, or the prothorax separate, are to be considered above those in which the larval character of similarity among the thoracic segments is preserved.

By a parity of reasoning, those orders in which the appendages of the thoracic organs (the wings) are remarkably different in form must be considered as higher than the most nearly allied forms in which they are similar.

The sub-class therefore divides into orders as follows:§ Metamorphosis distinct; wings usually present;

Pupa inactive;

Mouth mandibulate;

Prothorax free; anterior wings corneous.

I. COLEOPTERA.

Thorax agglutinate; wings 4, membranous; posterior ones smaller.
II. HYMENOPtera.

Mouth haustellate; thorax agglutinate;

Anterior wings membranous, posterior abortive.
Wings 4, membranous, usually covered with scales.

III. DIPTERA.

IV. LEPIDOPTERA.

Pupa variable, sometimes active,* sometimes inactive; thorax variable; mouth mandibulate; wings 4, membranous, nearly equal.

V. NEUROPTera.

Those having an active pupa (BIOMORPHOTICA, Westwood) are now called Pseudoneuroptera, and are united by some authors with Orthoptera, with which, however, they appear to have but little affinity. The habits, as observed to me by Baron R. Osten Sacken, are quite different, the

Pupa active; wings 4; prothorax free;

Mouth mandibulate.

Mouth haustellate.

§§ Metamorphosis none; wings wanting;

Abdomen without appendages.
Abdomen with anal appendages.

VI. ORTHOPTERA.

VII. HEMIPtera.

IX. ANOPLURA.

X. THYSANOUra.

The order Neuroptera is very difficult to define, though the sub-orders composing it are very readily distinguished from any of the other orders.

Several so-called orders will by this scheme become attached to the orders here recognized, by possessing a majority of the characters above mentioned; thus the Strepsiptera become the Coleopterous family Stylopida; the Thysanoptera and Euplexoptera unite with the Orthoptera; the Aphaniptera with the Diptera, and the Trichoptera become a sub-order of Neuroptera.

Having thus exhibited the elementary characters upon which the orders are based, the special subject of the present treatise may now occupy the attention of the student.

In order that the body of the work may be made intelligible to the beginner, it will be necessary to make a brief exposition of the external anatomy of Coleopterous insects, before attempting to define the numerous families which compose the order. The three regions, the head, thorax, and abdomen, will therefore be taken up in succession.

HEAD.

The anterior portion of the body is called the head; it varies greatly in form, and is joined by membrane to the thorax. Usually the hind portion is but slightly narrowed, and enters the anterior part of the thorax; sometimes the part behind the eyes is suddenly narrowed, and constricted, forming the neck.

The surface of the head consists of a solid horny plate; above it is frequently marked by a single suture, running transversely between or in front of the antennæ; this is called the clypeal or frontal suture. The portion in front of this suture, when dilated so as to project over the mouth, as in many Scarabæidæ, is called the clypeus; when small, it is named epistoma, and is sometimes

Orthoptera being terrestrial, and using their wings only as accessaries in progression, while the Pseudoneuroptera are essentially aerial, passing the greater portion of the time on the wing.