are seldom seen unless one takes pains to look for them.

[Illustration: JELLY FISH]

All life comes from pre-existing life. So every animal living to-day has
come from some other living animal and every plant living to-day has
come from some other previously living plant. It is believed that the
first forms of life came from the water. At any rate, the oldest and
lowest forms of life to-day, the Protozoa, are found in the water. As
these are nearly all very minute and can be studied only with a
microscope, they are omitted from the suggested field work.

[Illustration: ANIMALS OF THE WHARF-PILES

Habitat Group in the American Museum of Natural History]

All who have access to the seashore have a wonderful opportunity to
study the Invertebrates. The long stretches of sandy beach, the
sections of shore 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 glass dish a whole new world
of creatures will be revealed--jellyfishes, ctenophores, 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 shaggy m