Economic entomology for the farmer and the fruit grower, and for use as a text-book in agricultural schools and colleges; economicentomolo00smit Year: 1906 STRUCTURE AND CLASSIFJCATION. 7^ 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
Economic entomology for the farmer and the fruit grower, and for use as a text-book in agricultural schools and colleges; economicentomolo00smit Year: 1906 STRUCTURE AND CLASSIFJCATION. 7^ 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 jDOwer that moves the animal. Centrally, the alimentary canal occupies a part of the body cavity, its size Fig. 12. Ideal section tiirough 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 inmiediately into innumerable branches, and this is the respiratory or breathing system. Frequently we find aroiuul the alimentary canal a con- siderable fatty mass, while everywliere through the insect body
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