Young Folks' Library: Wonders of Earth, Sea and Sky HTML version
The Organic World
(From The Elements of Science.)
ST. GEORGE MIVART F.R.S.
The number of all the various kinds of living creatures is so enormous that it would be
impossible to study them profitably, were they not classified in an orderly manner.
Therefore the whole mass has been divided, in the first place, into two supreme groups,
fancifully termed kingdoms—the "animal kingdom" and the "vegetal kingdom." Each of
these is subdivided into an orderly series of subordinate groups, successively contained
one a within the other, and named sub-kingdoms, classes, orders, families, genera and
species. The lowest group but one is the "genus," which contains one or more different
kinds termed "species," as e.g., the species "wood anemone" and the species "blue
titmouse." The lowest group of all—a species—may be said to consist of individuals
which differ from each other only by trifling characters, such as characters due to
difference of sex, while their peculiar organization is faithfully reproduced by generation
as a whole, though small individual differences exist in all cases.
The vegetal, or vegetable, kingdom, consists of the great mass of flowering plants, many
of which, however, have such inconspicuous flowers that they are [pg 358] mistakenly regarded
as flowerless, as is often the case with the grasses, the pines, and the yews. Another mass,
or sub-kingdom, of plants consists of the really flowerless plants, such as the ferns,
horsetails (Fig. 1), lycopods, and mosses. Sea and fresh-water weeds (algæ), and
mushrooms, or "moulds," of all kinds (fungi), amongst which are the now famous
"bacteria," constitute a third and lowest set of plants.
The animal kingdom consists, first, of a sub-kingdom of animals which possess a spinal
column, or backbone, and which are known as vertebrate animals. Such are all beasts,
birds, reptiles, and fishes. There are also a variety of remotely allied marine organisms
known as tunicates, sea-squirts, or ascidians (Fig. 2). There is, further, an immense group
of arthropods, consisting of all insects, crab-like creatures, hundred-legs and their allies,
with spiders, scorpions, tics and mites. We have also the sub-kingdom of shell-fish or
molluscs, [pg 359] including cuttle-fishes, snails, whelks, limpets, the oyster, and a multitude of
allied forms. A multitudinous sub-kingdom of worms also exists, as well as another of
star-fishes and their congeners. There is yet another of zoophytes, or polyps, and another
of sponges, and, finally, we have a sub-kingdom of minute creatures, or animalculæ, of
very varied forms, which may make up the sub-kingdom of Protozoa, consisting of
animals which are mostly unicellular.
Multitudinous and varied as are the creatures which compose this immense organic
world, they nevertheless exhibit a very remarkable uniformity of composition in their
essential structure. Every living creature from a man to a mushroom, or even to the
smallest animalcule or unicellular plant is always partly fluid, but never entirely so.
Every living creature also consists in part (and that part is the most active living part) of a
soft, viscid, transparent, colorless substance, termed protoplasm, which can be resolved
into the four elements, oxygen, hydrogen, nitrogen and carbon. Besides these four