It is estimated that four-fifths of the species comprised within the animal kingdom belong to the class of the Insecta. Fully one hundred and seventy-five thousand species of insects have already been named and described. Nevertheless vast territories teeming with insect life have been as yet only very imperfectly explored. The life-history and habits of only a few thousands of species have as yet been accurately investigated. There remains, therefore, a broad field for discovery and research in this portion of the animal creation.

Many insects are polygoneutic, that is, the species is represented by two or more annual broods, or generations, and thousands of individuals may, by careful treatment, be reared from the eggs of a single female. In the case of the higher animals the development and multiplication of individuals takes place but slowly, and it is obvious, therefore, that there is in the domain of insect life a far more convenient field for the investigation of the great problems of variation in animal forms, than among the vertebrate animals. Aberrant forms are not uncommon, especially among butterflies and moths, and are worthy of careful study. The various broods often present great and striking differences. The phenomena of seasonal and sexual dimorphism are nowhere more clearly developed than among the lepidoptera. Hybridization also often takes place between allied species of insects, especially in the case of the bombycid moths, and it is possible for the skilful entomologist to conduct investigations in this interesting department of inquiry with almost as much freedom and success as have attended the labors of the botanist in the domain of plant life.

The economic importance of the study of entomology can scarcely be overestimated. Some of the best friends of the agriculturist, as well as multitudes of his worst enemies, are found among the insects. The silkworm, the cochineal insect, and the bee have aided in the accumulation of many fortunes, and their culture has provided employment for millions of human beings. On the other hand, property worth millions of dollars is annually destroyed by insect ravages. It has been asserted by competent authorities that the depredations of the Codling moth (Carpocapsa Pomonella) have resulted, in a single year, within the limits of the State of Pennsylvania alone, in the destruction of fruit worth over a million of dollars, and the terrible Phylloxera at one time threatened the total overthrow of viticulture in Southern Europe.

Various schemes have been proposed for the classification of insects, and there is as yet only partial agreement among students upon this subject.

Insects belong to that great group of animals designated by zoologists as the Arthropoda. As a means of assisting to a better understanding of the practical hints and suggestions which follow, a sketch of the classification of the Arthropoda is here given.

ARTHROPODA.

Animals possessing an external skeleton composed of chitinous rings, or somites, and provided with articulated limbs.

Ceratophora.

• Class I. Peripatidea (Genus Peripatus).
• Class II. Myriapoda.
• Orders:
• 1. Diplopoda (Galley-worms, etc.).
• 2. Pauropida (Genus Pauropus, etc.).
• 3. Chilopoda (Centipedes, etc.).
• Class III. Hexapoda (Insects proper).
• Orders:
• 1. Thysanura.
• Sub-orders:
• Collembola (Podura, Spring-tails).
• Symphyla (Scolopendrella).
• Cinura (Bristle-tails, etc.).
• 2. Dermatoptera (Ear-wigs).
• 3. Pseudoneuroptera.
• Sub-orders:
• Mallophaga (Bird-lice).
• Platyptera (Stone-flies, Termites, etc.).
• Odonata (Dragon-flies, etc.).
• Ephemerina (May-flies, etc.).
• 4. Neuroptera (Corydalis, Ant-lion, Caddis-flies, etc.).

• 5. Orthoptera (Cockroach, Mantis, Mole-cricket, Grasshopper,
• Katydid, etc.).
• 6. Hemiptera.
• Sub-orders:
• Parasita (Lice).
• Sternorhyncha (Aphids, Mealy-bugs, etc.).
• Homoptera (Cicada, Tree-hoppers, etc.).
• Heteroptera (Ranatra, Belostoma, Water-spiders,
• Squash-bugs, Bed-bugs, etc.).
• 7. Coleoptera.
• Sub-orders:
• Cryptotetramera (Lady-birds, etc.).
• Cryptopentamera (Leaf-beetles, Long-horns, Weevils,
• etc.).
• Heteromera (Blister-beetles, Meal-bugs, etc.).
• Pentamera (Fire-flies, Skip-jacks, June-bugs,
• Dung-beetles, Stag-beetles, Rove-beetles, Water-beetles,
• Tiger-beetles, etc.).
• 8. Aphaniptera (Fleas).
• 9. Diptera.
• Sub-orders:
• Orthorhapha (Hessian-fly, Buffalo Gnats, Mosquitoes,
• Crane-flies, Horse-flies).
• Cyclorhapha (Syrphis, Bot-flies, Tsetze, Housefly,

• etc.).
• 10. Lepidoptera.
• Sub-orders:
• Rhopalocera (Butterflies).
• Heterocera (Moths).
• 11. Hymenoptera.
• Sub-orders:
• Terebrantia (Saw-flies, Gall-wasps, Ichneumon-flies,
• etc.).
• Aculeata (Ants, Cuckoo-flies, Digger-wasps, True
• Wasps, Bees).

Acerata.

• Class I. Crustacea (Barnacles, Crabs, etc.).
• Class II. Arachnida.
• Orders:
• 1. Acarina (Mites).
• 2. Araneina (Spiders).
• 3. Pedipalpi (Whip-scorpions, etc.).
• 4. SolpugÆ (Whip-scorpions).
• 5. Pseudoscorpii (False Scorpions).
• 6. Scorpiodea (True Scorpions).
• Class III. Pantopoda (Pyenogonida, Sea-spiders).
• Class IV. Tardigrada (Macrobiotus, etc.).
• Class V. Gigantostraca (Horse-shoe Crabs, Trilobites, etc.).
• Class VI. Linguatulina (Pentastoma, etc.).