In some of the stag- or wood-beetles (Fig. 82), which we may select as types, the adults are often found crawling about on or beneath the bark of trees, living on sap or small animals. The eggs laid in these situations develop into grub-like larvæ, which bore their way through living or dead wood, and in this condition sometimes live four or five years. They then transform into quiescent pupa (Fig. 82), which finally burst their shells and emerge in the adult form. Others, like water-beetles and the whirligigbeetles, whose mazy motions are often seen on the surface of quiet streams, pass the larval period in the water. Under somewhat different conditions we find the potatobugs, lady-bugs, fire-flies, and their innumerable relatives, but the changes they undergo in becoming adult are essentially the same as those described for the other members of the order.

132. The moths and butterflies (Lepidoptera).—The moths and butterflies occur all over the world. In their mature

FIG. 83.-Monarch-butterfly (Anosia plexippus). From photograph by A. L. MELANDER and C. T. BRUES.

state they are possessed of a grace of form and movement and a brilliancy of coloration that elicit our highest admiration. The mouth-parts are developed into a long proboscis, which may be unrolled and used to suck the nectar out of flowers, though in many of the adult moths, which never feed, it may remain unused. The wings, four in number, are covered with beautiful overlapping scales that

adhere to our fingers when handled. This feature, and the general plan of the body, which is much the same throughout the group, enables us to recognize most of them at once.

FIG. 84.-The silver-spot (Argynnis cybele). Photograph by A. L. MELANDER and C. T. BRUES.

133. The ants, bees, wasps, etc. (Hymenoptera).-The ants, bees, and wasps are the best-known insects belonging to this order. They are characterized by four membranous wings, by biting and sucking mouth-parts, and the female is often provided with a sting. All undergo a complete metamorphosis. The eggs may be laid in the bodies of other insects, or they may be placed in marvelously constructed homes, and be the objects of the greatest attention, the parents or attendants often risking or losing their lives in their defense. The members of this order have long attracted attention, largely on account of their remarkable instinctive powers. They live in highly organized communities, and certain of their characteristics may be illustrated by a study of some of the more familiar forms.

CHAPTER XI

ARTHROPODS (Continued). CLASS ARACHNIDA

134. General characters.-In this group, comprising the spiders, mites, and a large assemblage of related species, we again meet with great differences in form and structure which fit them for lives under widely different conditions. The three regions of the body, head, thorax, and abdomen, so clearly marked in the insects, are here less plainly defined. The head and thorax are usually closely united, and in the mites the boundaries of the abdomen are also indistinct. The appendages of the head are two in number, and probably correspond to the antennæ and mandibles of other Arthropods. In the scorpions and some species of mites these are furnished with pincers for holding the prey, and in other forms they act as piercing organs. Usually the thorax bears four pairs of legs, a characteristic which readily separates such animals from the insects.

The internal organization differs almost as much as does the external. In many species it shows a considerable resemblance to that of some insects, but in others, especially those of parasitic habits, it departs widely from such a type. Respiration is affected by means of tracheæ, or lung-books, which consist of sacs containing many blood-filled, leaf-like plates placed together like the leaves of a book.

Usually, as in the insects, the young hatch from eggs which are laid, but in the scorpions and some of the mites the young develop within the body and at birth resemble the parent. Almost all of these organisms live either as

parasites or as active predaceous animals upon other animals. For this purpose many are provided with keen senses for detecting their prey and poisonous spines for despatching it.

135. The scorpions.-Owing to the stout investing armor, the strong pincers, and the general form of the body, the scorpions might at first sight be mistaken for near relatives

of the crayfish or lobster. A more careful examination will show that the two pairs of pincers probably correspond to the antennæ and mandibles of the Crustacea that have become modified for seizing the food. The swollen part of the animal lying behind the four pairs of legs is a part of the abdomen, of which the slender "tail" constitutes the remainder. On the tip of the tail is a curved spine supplied with poison glands. Several pairs of eyes are borne on the dorsal surface of the head and thorax, while on the under side of the animal several slit-like openings lead into as many small cavities containing the lung-books.

FIG. 85.-Scorpion, showing pincer-like mouthparts and spine-tipped tail.

The scorpions are the inhabitants of warm countries, where they may be found under sticks and stones throughout the day. At night they leave their homes in search of food, which consists chiefly of insects and spiders. These are seized by means of the pincers, and the sting is driven into them with speedily fatal results. It is doubtful if the poison causes death in man, but the sting of some of the

larger species, which measure five or six inches in length, may produce certain disorders chiefly affecting the circulation. In this country there are upward of thirty species, most of which are comparatively small.

136. The harvestmen. The harvestmen or daddy-longlegs are small-bodied, long-legged creatures which resemble in general appearance several of the spiders. They differ from them, however, in the possession of claws corresponding to the smaller ones of the scorpion, and in their method of respiration, which is similar to that of insects. During the day they conceal themselves in dark crevices or stride slowly about in shaded places; but at night they emerge into more open districts and capture small insects, from which they suck the juices.

137. The spiders.-The spiders are world-wide in their distribution, and are a highly interesting group, owing chiefly to their peculiar habits. Examining any of our familiar species, it will be seen that the united head and thorax are separated by a narrow stalk from the usually distended abdomen. To the under side of the former are attached four pairs of long legs, a pair of feelers, and the powerful jaws supplied with poison-sacs, while eight shining eyes are borne on the top of the head. On the abdomen, behind the last pair of legs, are small openings into the lung cavities which contain a number of vascular, leaflike projections known as lung-books. In some species a well-marked system of trachea are also present. At the hinder end of the body are four or six little projections, the spinnerets, each of which is perforated with many holes. Through these the secretion from the glands beneath is squeezed out in the form of excessively delicate threads, often several hundred in number, which harden on exposure to the air. According to the use for which these are intended, they may remain a tangled mass or become united into one firm thread; and according to the habits of the animal, they may be used for enclosing their eggs,