Economic entomology for the farmer Economic entomology for the farmer and fruit-grower economicentomolo01smit Year: 1906 STRUCTURE AND CLASSIFICATION. 27 CHAPTER IV. MUSCLES, DIGESTION, AND CIRCULATION. Insects have no internal skeleton or bony structure, the body- wall serving for the attachment of muscles and to protect the inner organs. Cutting transversely through the thorax of an insect at its mid- dle, we find the greatest portion of the body cavity occupied by muscles, which are arranged in bundles attached to the entire inner surface of the body wall, proceeding to all the appendages,
Economic entomology for the farmer Economic entomology for the farmer and fruit-grower economicentomolo01smit Year: 1906 STRUCTURE AND CLASSIFICATION. 27 CHAPTER IV. MUSCLES, DIGESTION, AND CIRCULATION. Insects have no internal skeleton or bony structure, the body- wall serving for the attachment of muscles and to protect the inner organs. Cutting transversely through the thorax of an insect at its mid- dle, we find the greatest portion of the body cavity occupied by muscles, which are arranged in bundles attached to the entire inner surface of the body wall, proceeding to all the appendages, and thus providing the power that moves the animal. Centrally, the alimentary canal occupies a part of the body cavity, its size Fig. 12. Ideal section through an insect.—a, alimentary canal; h, heart; n, nerve-cord ; s, stig- mata ; t, tracheal tubes ; /, legs ; w, wings. depending considerably upon the kind of insect in hand. Just below the dorsal surface is a small tubular structure, at once the heart and only blood-vessel, while just above the ventral surface is a white, knotted cord,—the nervous system. Laterally, there is an opening on each side, from which a ringed tube leads into the body, dividing and subdividing almost immediately into innumerable branches, and this is the respiratory or breathing system. Frequently we find around the alimentary canal a con- siderable fatty mass, while everywhere through the insect body
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