The Object of a Field Trip.--Many of us live in the city, where the crowded streets, the closely packed apartments, and the city playgrounds form our environment. It is very artificial at best. To understand better the _normal environment_ of plants or animals we should go into the country. Failing in this, an overgrown city lot or a park will give us much more closely the environment as it touches some animals lower than man. We must then remember that in learning something of the natural environment of other living creatures we may better understand our own environment and our relation to it. On any bright warm day in the fall we will find insects swarming everywhere in any vacant lot or the less cultivated parts of a city park. Grasshoppers, butterflies alighting now and then on the flowers, brightly marked hornets, bees busily working over the purple asters or golden rod, and many other forms hidden away on the leaves or stems of plants may be seen. If we were to select for observation some partially decayed tree, we would find it also inhabited. Beetles would be found boring through its bark and wood, while caterpillars (the young stages of butterflies or moths) are feeding on its leaves or building homes in its branches. Everywhere above, on, and under ground may be noticed small forms of life, many of them insects. Let us first see how we would go to work to identify some of the common forms we would be likely to find on plants. Then a little later we will find out what they are doing on these plants. [Illustration: An insect viewed from the side. Notice the head, thorax, and abdomen. What other characters do you find?] How to tell an Insect.--A bee is a good example of the group of animals we call _insects_. If we examine its body carefully, we notice that it has three regions, a front part or _head_, a middle part called the _thorax_, and a hind portion, jointed and hairy, the _abdomen_. We cannot escape noting the fact that this insect has wings with which it flies and that it also has legs. The three pairs of legs, which are jointed and provided with tiny hooks at the end, are attached to the thorax. Two pairs of delicate wings are attached to the upper or _dorsal_ side of the thorax. The thorax and indeed the entire body, is covered with a hard shell of material similar to a cow's horn, there being no skeleton inside for the attachment of muscles. If we carefully watch the abdomen of a living bee, we notice it move up and down quite regularly. The animal is breathing through tiny breathing holes called _spiracles_, placed along the side of the thorax and abdomen. Bees also have compound eyes. Wings are not found on all insects, but all the other characters just given are marks of the great group of animals we call _insects_. [Illustration: Part of the compound eye of an insect (highly magnified).]