Habitat Group in the American Museum of Natural History]

All who have access to the seash.o.r.e have a wonderful opportunity to study the Invertebrates. The long stretches of sandy beach, the sections of sh.o.r.e covered with water-rolled pebbles and stones, even the steep, jagged cliffs, are all pebbled with these animals of the sea.

Twice every twenty-four hours the sea water creeps slowly up the beach until high water is reached, and twice every twenty-four hours it recedes again toward the ocean. It is therefore about twelve hours from one low water to the next. On a gently sloping beach, the distances between the high water mark and the low water mark may be many hundreds of feet, while on a steep beach or a straight cliff this area may be only a few feet in width. It is this area between the high and low water marks that is the haunt of many Invertebrates. These are animals that can live if they are not continually covered with water. Here are the rock barnacles, the soft clams, crabs of many kinds, beach fleas, numerous sea worms in their special houses, snails, and hermit crabs.

Others will be found in the pools between the rocks or in the crevices of the cliffs, which as the tide falls becomes great natural aquaria.

Here will be found hydroids, sea-anemones, starfishes, sea-urchins, barnacles, mussels. In the shallow water, crabs and shrimps are crawling along the sandy bottom or are lying concealed in the mud, while schools of little fishes scoot across the pool. If a fine silk net is drawn through the water and then emptied into a gla.s.s dish a whole new world of creatures will be revealed--jellyfishes, ctenoph.o.r.es, hydroids, eggs of fish, tiny copepods, the larvae or young of sea-urchins, starfishes, or oysters. If an old wharf is near by, examine the posts supporting it.

The pilings seem to be coated with a s.h.a.ggy ma.s.s of seaweed. Sc.r.a.pe some of this off and put in a dish of water. Sea-spiders, starfishes, hydroids that look like moss, sea-anemones, many varieties of worms, mussels and crabs are all living here.

[Ill.u.s.tration: UNDER THE SEA BED

Marine Worms, Whelk, Pecten or Scallop and Periwinkle]

Begin your study of these seash.o.r.e animals with a stroll along the beach. Examine the windrows of seawrack or seaweed. Whole troops of sandhoppers rise ahead of you. Oftentimes animals from distant sh.o.r.es or deep water will be found. The empty sh.e.l.ls have many a story to tell.

The papery egg-cases of the periwinkle remind one of a beautiful necklace. The air bubbles rising from the sand or mud as the wave recedes mark the entrance to the burrows of worms. Stamp hard on the sand. A little fountain of water announces the abode of the soft clam.

Watch the sand at the edges of the rippling water. The mole-crab may be seen scuttling to cover. In the little hollows between rocks a rock-crab or a green-crab may be found on guard.

[Ill.u.s.tration: WHELK (FULGUR Ca.n.a.lICULATA) AND EGG-CASES

Common Mollusk Found on Sandy Sh.o.r.es Along the Atlantic Coast of the United States.]

For collecting in the pools and shallow water a fine-meshed net is desirable. Many of the animals can be caught and placed in gla.s.s dishes of sea water for close observation.

[Ill.u.s.tration: Group showing a starfish attacking an oyster; soft sh.e.l.led clams; hermit crabs; fiddler crabs, etc.]

_A few animals that may be found at the seash.o.r.e:_

_Rocky Sh.o.r.es_--Hydroids on the rock-weed, rock-barnacles, snails, amphipods, lobsters, and oysters.

_Sandy Sh.o.r.es_--Worms, in tube houses, mole-crab, sand-hopper, egg-cases, whelks, shrimps.

_Muddy Sh.o.r.es_--Snails, clams, worms of many varieties, mud-crabs, hermit-crabs, blue crabs, scallops.

_Wharves and Bridges_ (on the piling)--Sponges, hydroids, sea-anemones, ascidians, starfishes, sea-urchins, worms.

On the sh.o.r.es of lakes, ponds, and streams will also be found many invertebrates.

[Ill.u.s.tration: HUMMINGBIRD MOTH

Range: Eastern North America. The larvae or caterpillars of this moth feed upon virburnum, s...o...b..rry and hawthorn.]

[Ill.u.s.tration: SEVENTEEN-YEAR CICADA OR SEVENTEEN-YEAR "LOCUST"

Range: Eastern United States. Pupae emerging from the ground. Detail from Group in the American Museum of Natural History.]

Insects play an important part in Nature's activities. From the point of view of man some are beneficial and some are destructive. In the former group may be mentioned the Dragonflies which feed upon mosquitoes, the Cochineal insects of Mexico, which furnish a dye-stuff, the Lady-bird beetles, which in the larval stage feed upon plant lice; the scale insects of India, which furnish sh.e.l.lac; the b.u.mblebees, which cross-pollinate the clover, and the Wasps, which fertilize the figs. Dr.

Lutz says that the manna which fed the Children of Israel was honeydew secreted by a scale insect, and that it is still eaten.

[Ill.u.s.tration: SEVENTEEN-YEAR CICADA OR SEVENTEEN-YEAR "LOCUST"

Range: Eastern United States. The pupa climbing tree trunk. Then it bursts its h.o.r.n.y outer skin and crawls out an adult.]

The Silkworm and the Honey-bee have been domesticated since prehistoric times, the former supplying a valuable fiber for clothing and the latter an important article of food.

Among the injurious insects a few may be mentioned: the House Fly or Filth Fly, which may carry disease germs on its feet to the food that we eat; the mosquitoes, which transmit yellow fever and malaria, the rat flea, which carries bubonic plague; the weevils, which destroy rice, beans, chestnuts, etc., and the plant lice, or aphids, which, by sucking the juices from ornamental and food plants, are among the most destructive of all insects.

There are so many insects in the world that we cannot hope to learn of them all, even if we wanted to do so, but most of us wish to know the names of those that attract our attention, and to know what they do that is important or interesting. There are approximately 400,000 species or kinds of insects known in the world; that is, about three times as many as there are species or kinds of all the rest of the animals in the world put together. This fact should not hinder us from making a start and becoming familiar with the interesting habits of a few of the insects about us.

The eggs of the Monarch b.u.t.terfly may be collected upon the milkweed and brought in, so that the whole life history or metamorphosis of this beautiful insect, from the egg through the larva or caterpillar stage and the pupa or chrysalis stage to the adult b.u.t.terfly, may be watched.

The larvae or caterpillar must be supplied daily with fresh milkweed leaves. Other b.u.t.terflies and moths and many other insects may be reared in the same way by supplying the larvae with suitable food. If we should find a caterpillar feeding upon the leaves of a maple tree we should continue to feed it maple leaves if we wish to rear it. Silkworms will eat the leaves of Osage-orange, but they seem to prefer mulberry leaves.

Coc.o.o.ns of moths may be easily collected in winter after the leaves have fallen, and brought in and kept in a cool place until spring when the coming out of the adult moths will be an occurrence of absorbing interest.

[Ill.u.s.tration: "A GATHERING OF MONARCHS"

Monarch b.u.t.terflies resting during migration. The Monarch ranges all over North and South America and it migrates like the birds. Photograph of group in American Museum of Natural History.]

The spiders, although not insects, are interesting little animals. See how many types of webs you can find. Mention a few insects which you know to be preyed upon by spiders. Mention one insect that catches spiders and stores them away as food for its young.

[Ill.u.s.tration: TRACKS OF THE GLACIER

North America at the time of the maximum stage of the Great Ice Age, showing area covered by ice. (After Chamberlin and Salisbury).

Photograph used by courtesy of Henry Holt & Co.]

[Ill.u.s.tration: THE KING OF THE NORTHLANDS]

GEOLOGY

_Finds tongues in trees, books in the running brooks, Sermons in stones, and good in everything._ --_Shakespeare, As You Like It._

The Structure and History of the Earth

There is nothing eternal about the earth except eternal change, some one has said. It requires only a little looking about us to see that this is true. The earth is not as it was in the past. Every shower of rain changes or modifies its surface. And many other and some very great changes have occurred during the past few millions of years. During one age, the coal was formed of plants that grew luxuriantly on the earth's surface. At one period in the development of the earth there were many kinds of invertebrate animals, but no animals with backbones. Later, the vertebrates appeared. At one time the whole Mississippi Valley was under the water of the sea. ("The Story of Our Continent," by N. S. Shaler.

Ginn & Co.). These statements suggest just a few of the things that have been going on in the history of the earth. By the study of Geology we can learn much more about it, and we should supplement our study of books with the more important actual observation of conditions out-of-doors. To those living in that part of North America, which is shaded in the map on page 451, the easiest and most natural approach to the subject of the structure and history of the earth is by studying the effects of the continental glacier which formerly moved down over this region.

Tracks of the Glacier

When we see the foot-prints of an animal in the mud or in the snow, we are sure that an animal has pa.s.sed that way at some previous time. Those who live in Canada or northern United States (See map page 451) can be just as sure that a great glacier or ice-sheet formerly moved down over northern North America, by the tracks it has left. Although it is estimated by geologists that between 10,000 and 40,000 years have elapsed since the Great Ice Age, these tracks or evidences can still be seen by any one who lives in this region or who can visit it. The princ.i.p.al ones are: (1) Boulders or Lost Rocks which were brought down by this glacier; (2) The Glacial Drift or Boulder Clay which covers nearly all of the glaciated region; (3) Scratches on the bed-rock which show the direction the glacier moved.

Notice in the field the size and shape of the glacial boulders, where they are found, evidence of the place where the glacier melted off (terminal moraine). Do these boulders increase or decrease in size as we go south over the glaciated area? Can you discover any place where they can be traced back in their native ledge? Present-day glaciers, like the Muir Glacier in Alaska, can be seen transporting boulders and drift just as this great prehistoric ice-sheet must have done.

The drift which consists of clay mixed with pebbles, cobblestones, and boulders, varies greatly in depth. In some places there is none, while at St. Paris, Ohio, it is 550 feet deep. It probably averages 100 feet thick or less.

In your locality note the depth of the drifts in cuts made naturally by creeks and rivers or those made artificially for railroads. Oil-wells furnish evidence on this point. Collect a few good examples of scratched or glaciated pebbles or cobblestones which are abundant in the drift.

These were scratched while frozen in the bottom of the glacier and pushed along on the bed-rock under the weight of the ice above.