Popular Scientific Recreations / in Natural Philosphy, Astronomy, Geology, Chemistry, etc., etc., etc.

by Gaston Tissandier

Where there is vegetation there are animals, not quadrupeds or bipeds necessarily, but numbers of small, it may be invisible, creatures which exist upon the vegetable kingdom—the algæ and minute creations of globules and cells, the infusoria already mentioned, the corals, etc. And in the “protozoa,” or first specimens of animal life, we have a similarity to the vegetable kingdom; we then get by gradual steps to other more perfect beings, each after his kind, till we arrive at the most perfect animal—Man.

Animals are divided into two families, the Invertebrate and the Vertebrate. The former has no spine nor skeleton; the latter has both. These again are divided into sub-families, classes, and orders, as follows.

Man is an animal—but what is an animal? We can scarcely tell in a few words. Linnæus defined the difference between the animal and the plant, for the former, said he, live, grow, and feel, while the latter live and grow. We have protozoa in the animal kingdom consisting of a single cell or blood corpuscle, some others without mouths or digestive organs, some have no head; some, as in the tape-worm, only a so-called head, with suckers or attachments, after which it develops joints, which are at first imperfect, but gradually mature as they are pushed farther away by new-issuing joints.

Animals, therefore, do not all possess organs, nor is there any common organ by which all animals can be classed. The indispensable in one is absent in another, and while our mouths and digestive apparatus are all important, in other animals suckers and no digestive apparatus at all is quite sufficient. Some have one mouth, some several; some have mouths and a proboscis to assist them, some only the trunk and no mouth—so called—at all, as in some insects.

Fig. 827.—Polypidom.

The organisms which could not be distinguished from vegetables were termed zoophytes, or plant animals, and, were space available, a comparison might be instituted between the extremes of growth of the animals and plants, from the largest whales to the tiny microscopic protozoa, and from the mould upon jam to the gigantic trees of California, one leaf of which it is said will shelter twenty men from rain.

Cuvier spent many years in perfecting his systematic arrangements of animals, and this classification, though many rearrangements have been made as modern discovery progressed, may be regarded as the fundamental system of all. Professor Agassiz adopted it with modifications. Professor Nicholson has made a somewhat different arrangement, but essentially there will be found but slight difference between them. We append both these arrangements for comparison:—

Agassiz-Cuvier.
INVERTEBRATA.
Branch I.—Radiata.
Class I.—Polypi	2 orders	Including actinoids and halcyonoids.
Class II.—Acalephs	3 orders	hydroids, discophoræ, ctenophoræ.
Class III.—Echinoderms	4 orders	crinoids, asteroids, echinoids.
Branch II.—Mollusca.
Class I.—Acephala	4 orders	bryoza, brachiopods, tunicata, and lamellibranchiata.
Class II.—Gasteropoda	3 orders	pipteropoda, heteropoda, and gasteropoda (proper).
Class III.—Cephalopoda	2 orders	tetrabranchiata, and dibranchiata.
Branch III.—Articulata.
Class I.—Worms	3 orders	trematods (including leeches, etc.), nematoids, and annelides.
Class II.—Crustacea	4 orders	rotifera, crinopods, tetradecapods, and decapods.
Class III.—Insects	3 orders	myriapods, arachnoids, and insects proper.
Branch IV.—Vertebrata.
Class I.—Myzontes	2 orders	myxinoids and cyclostomes.
Class II.—Fishes proper.
Class III.—Ganoids	3 orders	cælacanths, axipenseroids, and sauroids.
Class IV.—Selachiens	3 orders	chimæræ, galeodes, and batides.
Class V.—Amphibians	3 orders	cæciliæ, ichthyodi, and anoura.
Class VI.—Reptiles	4 orders	serpents, saurii, rhizodontes, and testudinata.
Class VII.—Birds	4 orders	natatores, grallæ, rasores, and incessores.
Class VIII.—Mammalia	3 orders	marsupiaia, herbivora, and carnivora.

In the vertebrated animals the blood is red in consequence of the minute cells (corpuscles) which contain the colouring matter. In invertebrate animals these red cells are absent, and so the animals are white-blooded. Some animals, again, are cold-blooded like the fish; birds and mammalia have warm blood. It is worthy of remark that the higher we advance in the scale the fewer the offspring of the animal. The animalcules multiply at the rate of many billions a day, and even one codfish is stated to contain more than nine millions of eggs. A mackerel will produce 500,000; and so on, as we rise, we find mammals with seldom more than ten young at a time, down to one single offspring.