it may be that the larva, by its presence there, causes the unnatural growth of the leaf, resulting in a wart or tumor, and sometimes in a large round nut. It is believed, however, that the adult insect, in depositing the egg, also stings the leaf, and, poisoning it at the same time, induces the abnormal growth of the leaf. Within this the larva feeds,

FIG. 102.-GALL-NUT ON OAK-LEAF.
(Copied from Harris's "Insects injurious to Vegetation," third edition.)

and changes into the pupa state, and finally into the perfect insect, when it gnaws its way out.

In the autumn the pupils will find the gall-nuts abundantly in the woods. Let them collect a number of these, and, on carefully cutting them open, they will find within a tiny oval case, and upon opening this they will discover snugly stowed away a little, polished black fly having four wings. The creature when liberated is ready to fly away.

Some of the nuts will be empty, because the gall-insects have already escaped.

Galls are also produced by other kinds of insects. The following figure, which represents a gall common on the golden-rod, is produced by a two-winged fly. The figure represents the stem or stalk unnaturally swollen, the swollen portion being the gall, within which the larva, pupa, or perfect insect, may be found if the creature has not already escaped.

p

FIG. 103.-GALL ON GOLDEN-ROD STALK.-P, Pupa removed from the Gall.

Let the pupils arrange in their collecting-box a leaf with the nut attached, a nut cut open showing the pupa-case, and the insect pinned.

97. Only a few brief lessons have been given representing the life-history of a butterfly, mud-wasp, mosquito, spit

tle-insect, seventeen-year cicada, May-fly, and gall-fly. Let the pupils endeavor from their own observations to make additional life-histories, or record facts, concerning other insects, such as the honey-bee, paper-wasp, and a great many other common insects, of which no mention has been made here. The turning over of stones and logs in the woods will oftentimes expose the burrows of ants, and the ants will probably be found busily engaged in carrying off long, white, oval cases, which look like eggs; let the pupils collect some of these, and see if they can find out what stage in the history of the insect they represent.

98. An instinct which appears wonderful to us, prompts the insect to seek appropriate places for the deposition of her eggs. The butterfly, for example, seeks for food the nectar of flowers; its larvæ, however, must have leaves upon which to feed, and the instinct of the butterfly impels it to deposit its eggs in a place where the young shall find their appropriate food. It has been learned also that other insects store up animal food for their young, as in the case of the mud-wasp, where spiders are imprisoned in cells in which the eggs have been previously laid.

The gall-flies deposit their eggs directly in the substance of the leaf.

99. Another group of insects, much resembling the gallflies, deposit their eggs directly in the bodies of the larvæ and pupa of other insects. They are called ichneumonflies. These insects have on the hinder part of the body a

sharp, piercing sting, and with this organ the necessary hole is made through which the egg is deposited.

A caterpillar soon hatches from the egg thus deposited by the ichneumon-fly, and feeds upon the fatty portions of the body of the larva in which it has been so placed. But this larva containing the ichneumon-caterpillar, meanwhile, completes its growth and changes into a chrysalis, when the inclosed ichneumon-larva devours the entire contents of the chrysalis, and then changing into the pupa state soon emerges as an ichneumon-fly, to go in quest of caterpillars, in which to deposit its eggs. Thus it will often happen that a number of cocoons have been collected, from which ought to appear a certain kind of moth, for example, but from many of them a brown ichneumon-fly will emerge, a sight quite as startling, to one not familiar with insects, as if a robin should be seen to hatch from a hen's egg.

If the pupils will collect from the fences a large number of the chrysalides of the common yellow cabbage-butterfly, and keep them in a box, with a piece of glass for a cover, they will observe that while butterflies come from many, from others, which have already changed to a lighter color, little black flies will appear, crawling out of holes in the side of the chrysalis which have been made by some of the imprisoned ichneumons. (See Fig. 104.)

100. Nearly every species of insect is infested with one or more species of ichneumons, which deposit their eggs either within the pupæ, larvæ, or the eggs themselves.

There are some species of ichneumons which deposit their

eggs within the eggs of the canker-worm moth, and, as tiny as these eggs are, they are still large enough to furnish nourishment and room for the complete development of the insect feeding within.

In Fig. 74 an ichneumon-fly is shown on the wing, in search of caterpillars wherein to deposit her eggs.

Fig. 67 also represents an ichneumon-fly of large size. Fig. 104 represents ichneumon-flies escaping from the chrysalis of the cabbage-worm butterfly.

FIG. 104.-CHRYSALIS OF THE CABBAGE-WORM, FROM WHICH ARE SEEN ESCAPING ICHNEUMON-FLIES.

CHAPTER XV.

SPIDERS.

101. For this lesson the pupils are to collect a number of spiders, securing, if possible, the largest specimens. A wide-mouthed bottle, with a little alcohol, will answer to collect them in. Let each pupil select the largest specimen to study, and pin it to a piece of cork, or to a soft pine strip. The legs are to be arranged with two pairs pointing forward and two pairs pointing backward, as shown in Fig. 105.

Let them study the following characters with the specimen before them :

The spider is divided into two regions. That region or part to which the legs are attached is called the cephalo