there is no notch, or fold, in it. In the three upper figures there is a notch, or fold, in the base of the aperture.

FIG. 27.-SHELL SHOWING LONG CANAL.

This notch is called the canal, and in some species it is very short, while in other species it is very long, as in Fig. 27.

The mantle of the animal is prolonged in a fold which occupies this canal, and is called the siphon. Through this fold or siphon the water finds access to the gills. (Fig. 28 shows another species. The siphon is seen as a fold of the mantle running into the canal of the shell.)

23. A very common species, found in the greatest abundance from Maine to Florida, on mud-flats, will give a good

illustration of the uses of the siphon. In this particular species, the siphon is much longer than the canal, and, when the snail is crawling, the siphon is bent upward. As the

Foot or Creeping Disk.

m

FIG. 28.-A SEA SNAIL SEEN FROM BELOW.-e, Eye; m, Mouth; 8, Siphon.

habit of this species is to crawl along partly buried in the mud, the siphon, projecting above the level of the mud, conducts the pure sea-water to the gills of the snail below. Fig. 29 illustrates the appearance of this snail:

FIG. 29.-A, the Snail crawling upon the Surface of the Mud; B, the same slightly buried; C, the same nearly buried; the Siphon, 8, is seen curved upward.

Such shells are called canaliculated shells,

The aperture of the shell is said to be entire, when it does not possess this notch, or canal. Let the pupil separate the shells having the aperture entire, from those shells having a canal.

These differences in the shell, as slight as they appear, are accompanied by corresponding differences in the character and habits of the animal.

Those snails having the aperture of the shell entire are with few exceptions vegetable-feeders, while those having a canal to the shell are flesh-feeders. The mouth-parts, and opercula, too, are different in the two groups.

24. Other shells will be found differing greatly in appearance from those thus far studied. One of these is represented in the lower left-hand corner of Fig. 26.

Another species, called the limpet, looks like this (Fig. 30):

FIG. 30.-SHELL OF LIMPET.

These shells will be found sticking with great tenacity to the rocks, and some skill and force will be required to remove them. This can be done by using the large blade of a pocket-knife, and suddenly scraping them from the rock. If they are then placed in a saucer of water, with the shell downward, the animal within will be found to have the broad, creeping disk, head, tentacles, and other parts, peculiar to the snails already studied.

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 proportional 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 scen.

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.

b

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

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