But every living creature consists at first entirely of a particle of protoplasm.  Therefore every other kind of substance which may be found in every kind of plant or animal, must have been formed through it, and be, in fact, a secretion from protoplasm.  Such is the rosy cheek of an apple, or of a maiden, the luscious juice of the peach, the produce of the castor-oil plant, the baleen that lines the whale’s enormous jaws, as well as that softest product, the fur of the chinchilla.  Indeed, every particle of protoplasm requires, in order that it may live, a continuous process of exchange.  It needs to be continuously first built up by food, and then broken down by discharging what is no longer needful for its healthy existence.  Thus the life of every organism is a life of almost incessant change, not only in its being as a whole, but in that of all its protoplasmic particles also.

[Illustration:  FIG. 4.  AMOEBA SHOWN IN TWO OF THE MANY IRREGULAR SHAPES IT ASSUMES. (After Howes.)

The clear space within it is a contractile vesicle.  The dark body is the nucleus.  In the right-hand figure there is shown a particle of food, passing through the external surface.]

Prominent among such processes is that of an interchange of gases between the living being and its environment.  This process consists in an absorption of oxygen and a giving-out of carbonic acid, which exchange is termed respiration.

Lastly, protoplasm has a power of motion when appropriately acted on.  It will then contract or expand its shape by alternate protrusions and retractions of parts of its substance.  These movements are termed amoebiform, because they quite resemble the movements of a small animalcule which is named amoeba. (See Fig. 4.)

Such is the ultimate structure, and such are the fundamental activities or functions of living organisms, as far as they can here be described, from the lowest animalcule and unicellular plant, up to the most complex organisms and the body of man himself.

[Illustration]

INHABITANTS OF MY POOL

(FROM MAGIC GLASSES.)

BY ARABELLA B. BUCKLEY.

The pool lies in a deep hollow among a group of rocks and boulders, close to the entrance of the cove, which can only be entered at low water; it does not measure more than two feet across, so that you can step over it, if you take care not to slip on the masses of green and brown seaweed growing over the rocks on its sides, as I have done many a time when collecting specimens for our salt-water aquarium.  I find now the only way is to lie flat down on the rock, so that my hands and eyes are free to observe and handle, and then, bringing my eye down to the edge of the pool, to lift the seaweeds and let the sunlight enter into the chinks and crannies.  In this way I can catch sight of many a small being either on the seaweed or the rocky ledges, and even creatures transparent as glass become visible by the thin outline gleaming in the sunlight.  Then I pluck a piece of seaweed, or chip off a fragment of rock with a sharp-edged collecting knife, bringing away the specimen uninjured upon it, and place it carefully in its own separate bottle to be carried home alive and well.