the pupil may get these clusters. Before studying a specimen, it is best to clean the shell thoroughly in water by means of a coarse brush.

44. Instead of having two adductor muscles, it has but one (though this muscle, it seems, is composed of two elements). A single dark-purple mark on the inside of each valve shows the point of attachment of the adductor muscle. When the oyster is opened, the mantle contracts somewhat, so that the edge of the mantle is some way from the margin of the shell, as shown in Fig. 47.

The left valve is the larger, and is the one that becomes attached; the right valve is flattened, and somewhat smaller. The mantle has its margins free; that is, the edges are not united as in the common clam, where they are not only united, but greatly thickened. Neither is the mantle prolonged into siphons as in other species; consequently, the water flows in at one portion of the shell, and pours out of another portion, not being definitely conducted by special channels, as in those forms heretofore given. The oyster can be readily studied, as specimens may be got in almost every village in the country.

In looking over canned specimens, be sure and pick out a large one, and one that does not appear to be mutilated, as they frequently are when taken out of the shell by the oysterman, or jammed, as they often are in packing.

To those who can get them alive, it is well to have the oysterman open the specimen, being sure that he removes the larger valve, leaving the oyster attached, and resting in

To ex

the smaller and flat valve, which is the right one.
amine it properly, the specimen must be placed in a deep
saucer filled with water, so as to cover it. A number of
rinsings will remove the mucus with which the oyster is
covered, and this will render the specimen in better con-
dition to examine. In placing it under water in this way,
the membranes float apart, and can be more readily
studied.

45. The adductor muscle is near the middle of the animal. It is composed of two elements, one half being a glistening white, and the other half being grayish. Immediately adjoining the grayish portion of the muscle, a translucent space is seen, and this space contains the heart, composed of a body constricted in the centre, as if a tube had been tied in the middle by a string. This is the heart proper, and in specimens freshly opened the heart may be seen to slowly pulsate, or beat.

By raising the mantle, the gills will be seen as delicate, leaf-like membranes.

At the smaller end of the oyster, and that portion which comes next to the beak or hinge, the mouth will be found having on each side two delicate lappets, which are called the palpi. It will be difficult to find the mouth, and some patience will be demanded in lifting the mantle and following up between the palpi to where the mouth is.

The dark region just back of the mouth contains the stomach and liver; the dark or blackish portion, showing so conspicuously in cooked specimens, being the liver.

1

By referring to the accompanying figures, these parts may be readily made out :

FIG. 47.-OYSTER WITH THE LEFT VALVE REMOVED.-h, Heart; 7, Ligament; m, Position

of Mouth.

46. The pupil will now recall some characters in common between the snails, and the mussels, clams, and oysters, thus far studied in these lessons, namely: they all have the body protected by a limy shell (except the slug), this shell either composed of one piece, as in the snails, or of two pieces or

FIG. 48.-RIGHT VALVE OF AN OYSTER, the Dark Semicircular Mark near the Middle of the Shell being the Adductor Muscular Impression, the Pallial Line showing faintly.

valves, as in the clams, mussels, and oysters. All of them increase the size of their shells, or grow, by the addition of layers of shell-material to the edge of the aperture, or the margins of their valves, and these layers are inIdicated by delicate lines on the outside of the shell, and called lines of growth. They all, excepting the oyster and a few other forms, have the creeping disk or foot. In the snails, this is broad and flat; in the mussel and clam the foot is flattened sideways, and variously shaped. In the snails, the creature projects, with the foot, a head furnished with feelers, or tentacles, and the mouth is possessed of certain hard parts by which food can be eaten. In the mussels and clams there is no definite head, the mouth being hidden away within the mantle, and the creature projecting, from the forward end, only the foot. In all of these animals thus far studied there is a cavity within, containing the gills to which water has access, or else there is a simple

lung, as in the air-breathing snails. These, with the cuttlefishes, which we will not consider here, belong to a branch of the Animal Kingdom called Mollusca.

CHAPTER VII.

COLLECTING INSECTS.

47. THESE lessons, as well as the preceding ones, are prepared with the understanding that the pupils shall, so far as possible, make a collection of the species of animals studied. In fact, it is a part of the lesson to know how and where to collect, and above all to know how to preserve the specimens collected. To enable the pupils to do this, the briefest directions are given for the making of boxes, nets, etc., accompanied with the simplest methods of preserving the collections made.

In many cases the directions given are by no means the professional methods; thus the pupils are directed to use common pins for insects, while the professional collector uses only the true insect-pins made expressly for the purpose, but these are oftentimes difficult to procure, and are more expensive than the common ones.

In commencing these lessons, each pupil must first be provided with a number of common pins, and a box propery arranged in which to pin the insects collected.

Some holiday afternoon, or an hour before school-time

E