as it crawls around on the sides of the jar, he will see at intervals the mouth open, and a glistening tongue appear, as the snail laps up the scum which forms upon the surface of the glass.

NOTE FOR TEACHERS AND PUPILS.-Let the teacher here explain to the pupils what is meant by an object's being magnified.

If the teacher has a common magnifying-glass, let each pupil in turn observe its magnifying effect, by looking at a common house-fly, or the printed page of a book. If a microscope can be shown to the class, it will be better still.

Let it be explained, also, what is meant by an object being enlarged two, or three, or more times. To be enlarged two or three times, is to make the object two or three times as long as it was before, and of propor

tional size.

Oftentimes the object has to be reduced in size in the figure, as in pictures of large animals, in the picture of an elephant, for example.

In representations of very small animals, however, the figure has to be enlarged in order to show parts plainly that could not otherwise be seen.

17. In searching for snails, the pupil will come across snail-like animals, which have no coiled shells on their backs. Let the pupil examine the under side of damp boards or plank walks in gardens, and he will be sure to find them.

They are very common in old gardens in cities. These

FIG. 21.--A SLUG CONTRACTED.

creatures will be found clinging to the board or upon the ground, and will present this appearance (Fig. 21). Soon, however, they will stretch out their tentacles, and commence

crawling, and then their resemblance to the shell-bearing snails will be seen at once.

Instead of having a coiled shell into which they can retreat when alarmed, they have a little limy scale imbedded in a portion of the back, called the mantle. The breathingorifice is on the right side of the body, and the tentacles, mouth-parts, creeping disk, and other features, are quite similar to the land snails already studied.

FIG. 22.--A NAKED LAND SNAIL, OR SLUG, FULLY EXPANDED.-a, Mantle; b, Ereathing

Orifice.

18. On the approach of winter, land snails bury themselves in the ground, and those that have shells retire within the shell as far as possible, and close the aperture of the shell with a film of the mucus which the body secretes so abundantly. In this condition they remain dormant until the warm weather of spring revives them again.

If the pupil will collect some snails in the early spring, and keep them confined in a box, with earth, damp leaves, or bits of rotten wood or bark, the snails in the course of a few weeks will lay a number of little eggs. These eggs will be white and round, about the size of a pin's-head. By careful tending, that is, by keeping the leaves slightly moist, the

eggs will hatch out tiny snails, and these will attain half their mature size the first season.

FIG. 23.-a, Eggs of Land Snail; b, Young Snail just hatched; c, Young Snail somewhat advanced: b and c are magnified.

19. If the pupil will also collect a lot of fresh-water airbreathing snails, and keep them alive, they will deposit their eggs upon the sides of the glass jar in which they are confined. These eggs will be oval in shape, and transparent, and will be inclosed in a transparent, jelly-like substance. Fig. 14, II, represents the appearance of a cluster of these eggs.

Fig. 24 shows a cluster of eggs with the appearance of two eggs highly magnified, showing the young snails as they appear within the egg.

FIG. 24.-a, Cluster of Eggs of a Fresh-Water Snail; b, c, Eggs enlarged, showing the young Snails within the Eggs.

With the aid of a magnifying-glass, the eggs may be watched from day to day, and the young snail can be seen in its various stages of growth.

20. If a land-snail is taken out of its shell (and this can be done if boiling water be first poured upon it, and then with a pin the animal can be readily picked out), it will present this appearance (Fig. 25):

m

FIG. 25.-LAND SNAIL REMOVED FROM ITS SHELL.-m, Mantle.

The portion contained within the shell presents the same general appearance as the shell itself. A free border, or collar, is seen which corresponds to the aperture of the shell. This border is called the mantle, and is a characteristic feature of all the snails thus far studied. It is the edge of the mantle which deposits the successive layers of the shell, and increases its size. In the slug, there is only the limy scale; this is buried in the mantle, which is plainly seen covering a portion of the back, like a shield (Fig. 22, a).

CHAPTER IV.

SEA SNAILS.

21. CLASSES that live near the sea-coast may now study the marine, or salt-water snails. These may be collected alive at low tide, upon rocks, or under the sea-weed. By

examining pools left at low tide, many little sea snails may be seen creeping about.

A good place to collect dead shells may be found along an exposed beach. After a violent storm, when the waves have been running high, a great many animals are thrown up from the sea, and among them many shells may be secured.

The following will be some of the shells collected :

FIG. 26.-COMMON SEA SNAILS.

22. With very few exceptions, all sea snails are waterbreathers; that is, they are furnished with gills, instead of a simple lung. Most of them are operculated.

In the shells collected the pupil will find two wellmarked groups.

In the two lower right-hand figures of Fig. 26, the shells have an aperture with a continuous border; that is,