The boxista gigantea, a species of fungus, has been known to increase its size more than a million times during a single night; and Ehrenberg speaks of an animalcule which prop-agates so rapidly that its descendants would ! in four days amount to 70 billions. - The sci-' entifie study of the animal kingdom constitutes the department of natural science termed zoology. Zoography is merely the description of animals; while zootomy, or comparative anat-omy, is the study of their structure, and zoon-omy, or comparative physiology, that of their functions. To facilitate these investigations, a scientific classification of the animal kingdom | was first published by Linnaeus in 1735, in his Systema Natural. This was improved by G. Cuvier, who spent 17 years in perfecting his | system (1795 to 1812), which, being based upon ! the structure of animals, is termed the anatomical system. Modifications have also been ! made by Lamarck, Virey, Dumeril, and De Blainville; but Cuvier's classification is still generally adopted.

He arranged the animal kingdom in four great divisions, viz.: I. The vertebrata (those animals having a spinal column), containing four classes - mammalia, birds, reptiles, and fishes.

II. The mollusca.

III. The articulate.

IV. The radiata. The classes are divided into 72 orders, and the latter into the different genera and species. The classification of Prof. Agassiz, founded on that of Ouvier, is one of the most modern, and in many respects one of the most instructive. It is as follows:

Branch I. Radiata. Class 1. Polypi: including the 2 orders, actinoids and hal-cyonoids. " 2. Acalephae: 3 orders - hydroids (including siphonophorae), discophorae and ctenophorae. " 3. Echinoderms: 4 orders - crinoids, asteroids, echi-noids, and holothurioids.

Branch II. Mollusca.

Class 1. Acephala: 4 orders - bryozoa (including the verticelke), brachiopods, tunicata, and lamellibranchiata. " 2. Gasteropoda: 3 orders - pteropoda, heteropoda, and gasteropoda proper. " 3. Cephalopoda: 2 orders - tetrabranchiata and dibranchiata.

Branch III.

ARTICULATA

Class 1. Worms: 3 orders - trematods (including cestoids, planariae. and leeches), nematoids (including acan-thoeephala and gordiacei). and annelides.

" 2. Crustacea: 4 orders - rotifera. entomostraca (including cirripeds). tetradecapods. and decapods.

" 3. Insects: Borders - myriapods, arachnids, and insects proper.

Branch IV. Vertebrata.

Class 1. Mysontes: 2 orders - myxinoids and eyclostomes. " 2. Fishes proper: 2 orders - ctenoids (as the perch) and cycloids (as the cod). [This division will probably be considerably moditied by its author.] " 3. Ganoids: 3orders - caelacanths. acipenseroids, and sauroids: and doubtful, the siluroids, plectognathi. and lophobranches. " 4. Selachians: 3 orders - chimaerae, galeodes, and batides. " 5. Amphibians: 3 orders - caaeciliae, iehthyodi, and anoura. " 6. Reptiles: 4 orders - serpents, saurii, rhizoilontes, and testudinata. " 7. Bird*: 4 orders - natatores. grallae, rasores. and insessores (including scansores and accipitres). " 8. Mammalia: 3orders - marsupialia, heroivora, and carnivora.

- As to the chemical composition of animals, probably only 17 out of the 64 simple elements now known, or at most 19, enter into their structure. These are:

Oxygen,

Hydrogen,

Carbon,

Nitrogen,

Copper,

Sulphur,

Phosphorus,

Calcium,

Iodine,

Lead,

Magnesium,

Sodium,

Potassium.

Manganese,

Iron,

Chlorine, Fluorine, Silicon, Bromine.

These elements, variously combined, form numerous compounds, termed the immediate principles of animal structures, of which in the mammalia there are about 90. Of these, some are of mineral origin, as water, common salt, and phosphate and carbonate of lime. Some are formed within the bodies of animals by disassimilation, as urea, uric acid, and creatine; and others still are obtained from vegetable and animal food for the nutrition of the tissues, as albumen, caseine, musculine, and fat, and hence exist as constituent elements in the latter. These immediate principles unite to form the tissues of which the parts and organs of animals are constituted. These are in the vertebrata as follows:

1. Epithelial Tissue:

A. Epidermis and its modifications - nails, hoofs, horns, scales, and shells.

B. Hair and its modifications - bristles, wool, and feathers.

2. Elastic Tissue, its properties much resembling those of gum elastic.

3. White Fibrous Tissue, in tendons, ligaments, etc, very strong and almost totally inextensible.

4. Osseous and Dental Tissues, in bones and teeth.

5. Areolar Tissue, connecting the various organs together.

6. Adipose Tissue, otherwise called fat.

7. Cartilage, in the joints, those of the ribs, etc.

8. Muscular Tissue, the source of motion.

9. Nervous Tissue, the seat of sensation and intelligence.

10. Membranes, cutaneous (skin), mucous, and serous.

11. Glands, the secretory organs.

12. Vessels, the blood vessels and the lymphatics.

The tissues of animals are developed directly from the vital fluid, the blood. This in all the vertebrata is red, from the presence of minute cells containing a colored fluid, and which are called the blood corpuscles. In the invertebrate animals no such corpuscles exist, and therefore the blood is colorless. Hence the division of animals into the red-blooded and the white-blooded. The blood of each animal in the central parts of the body has its peculiar natural temperature, that of man being 98° to 99° F. The temperature of all animals lower in the scale than birds is lower than that of human blood, and hence all these are called cold-blooded, while birds and the mammalia are termed warmblooded animals. - The fecundity of animals also varies inversely with their elevation in the scale. While mammals produce from 1 to 8 or at most 10 young at a time, a tench produces 38,000 and a mackerel 546,000 eggs; and Leeuwenhoeck professes to have counted 9,384,-000 eggs in a single codfish. Some of the mammals are, however, very prolific. Pennant calculates that the descendants of a single pair of rabbits would, without interference, amount in four years to 1,274,840. But external circumstances exert a powerful influence in this regard.