With few exceptions worms live in the water, and even those which live on the land are limited to damp earth or moist places. While the larvæ of insects are in many cases aquatic in their habits, and breathe or respire by means of gills, the larger number live on the land, feeding on leaves, wood, and substances of a similar nature, and are airbreathers.

CHAPTER XI.

HABITS AND STRUCTURE OF INSECTS.

81. LET the pupils now endeavor to study the habits of certain insects by direct observation. The following sketches are given as aids to the pupils in making independent observations on special insects.

Most insects make no provision for the larvæ, but leave them to take care of themselves, though usually the egg is deposited where the larva coming from it may find proper food at hand.

Other insects prepare cells or cavities in which they deposit their eggs, just as a bird builds a nest to hold its eggs. Certain insects, in preparing these cells, also lay up a store of food ready for the larva when it shall have hatched from the egg. Such is the case with the common mud-wasp. This insect makes a number of little chambers of mud, generally sticking them to the sides of a wall, or to the ceilings of sheds, barns, and attics. These pellets of mud are seen firmly plas

tered to the wall, rough and irregular in appearance, and at first sight might be mistaken for the work of some mischievous boy.

FIG. 84.-A MUD-WASP'S NEST, HAVING Two CELLS.

Fig. 84 represents their general appearance, for, rough as they appear, on close examination they are seen to be constructed very systematically-the soft clay of which they are built being laid on in alternate layers, looking something like a braid; while the upper portion, being built of looser and coarser material, is put on in irregular lumps. With a thin-bladed knife these mud-cells may be scraped off, and sometimes can be pulled away with the fingers. Upon opening them they will be found either filled with little spiders, or containing yellow-colored larvæ, pupæ in brown skins, or wasps. Their history is as follows:

82. When the mother-wasp gets ready to lay her eggs, she first builds these curious nests of mud, which she collects from the streets, or by the sides of brooks in clayey soil. Having finished one cell, she deposits therein an egg, and then collects a number of small spiders with which she completely fills the cell. After this is done she closes up the top of the

cell with looser mud. Thus she proceeds, constructing cell after cell, going through the same manoeuvres with each one. It has been observed that the wasp stings the spiders so as to paralyze, but not to kill them. Hence they remain alive but cannot struggle, and when the egg hatches, the little larva coming from it finds in these spiders a store of food on which to feed. These are gradually eaten, and thus room is made for the rapidly-growing larva which, having eaten all the spiders, passes into its pupa state surrounded by its brown chrysalis case, and finally emerges a perfect wasp, when it softens the mud-walls of its nest, by a fluid poured from its mouth, and gnaws its way out.

FIG. 85.-SHOWING A NEST OF FOUR CELLS CUT OPEN: a, representing a Cell with the Egg at the Bottom, and the remaining Space filled with Spiders; b, the Larva full-grown, after having consumed all the Spiders; c, the Pupa; and d, the Imago, or Perfect. Wasp, ready to come out.

Fig. 51 shows one of these mud-wasps pinned.

The pupils may collect these nests or cells in April or May, and by June the wasps will be ready to come out. If collected soon after they are made, the eggs may be found; if

a little later, the larva will be found feeding on the spiders; and, still later, the full-grown larvæ and pupæ appear.

In collecting for the cabinet, one nest should be cut open to show the cells and their contents.

83. The mosquito deposits her eggs on the surface of the water, sticking them together in such a way as to form a raft. From these eggs little black creatures hatch, which swim about with a quick, jerking motion. In this condition. they represent the larvæ. If the pupils will examine pools and ditches, or even the tubs and barrels of water which often stand about farm-houses, they will be very sure to find some of these animals. They are small and black, and by their

с

B

FIG. 86.-A, Larva; and B, Pupa of a Mosquito; c. Line showing Natural Sizef Larva; d, representing Water-Line.-The larva is seen with the hinder end of the body just projecting above the surface of the water, so that the air may enter through the little tube. The pupa is seen with the back just level with the surface of the water, and through the two tubes, on the back of the thorax, the air is being admitted to the body.

rapid, jerking motion cannot be mistaken. A number may be collected and placed in a jar of water, where all their changes, from the larval to the perfect state, may be watched. They will be seen coming to the surface of the water for air,

which they breathe in through openings in the hinder part of the body. Changes soon take place by which they assume the pupa state, and at this time they no longer breathe through the hinder portion of the body, but through two tubes on the back of the thorax. Finally, the pupal skin cracks open, and out crawls the perfect mosquito, for a while resting on the empty pupal case which floats in the water like a raft, and the insect remains supported in this way till the wings become fully expanded and dry, when it flies away.

CHAPTER XII.

HABITS AND STRUCTURE OF INSECTS (CONTINUED).

84. In certain groups of insects the young hatches from the egg, not as a caterpillar, but as a little insect having the body divided into three regions, possessing three pairs of jointed legs, and looking very much like the mature insect, except that it is very much smaller and has no wings.

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FIG. 87.-YOUNG GRASSHOPPER.-w, Wing just appearing.

In the grasshopper, for example, the animal does not pass through a series of abrupt changes, but the creature comes from the egg with the general proportion of the adult insect,