. Elements of zoölogy. Zoology. INSECTS. 101 shape. The tracheae connect with the exterior at various parts of the sides of the body, the openings (Fig. 114) being called spiracles, stigmata, or breathing-holes. The tubes extend over a greater part of the body (Fig. 115), bringing fresh air in contact with the blood in the tissues. This is even accomplished in the wings, so that they serve as lungs as well as organs of flight. Breathing seems to be accomplished by a contraction and expansion of the ab- dominal segments. Nervous System.—The nervous system of insects is made up of a chain of gan
. Elements of zoölogy. Zoology. INSECTS. 101 shape. The tracheae connect with the exterior at various parts of the sides of the body, the openings (Fig. 114) being called spiracles, stigmata, or breathing-holes. The tubes extend over a greater part of the body (Fig. 115), bringing fresh air in contact with the blood in the tissues. This is even accomplished in the wings, so that they serve as lungs as well as organs of flight. Breathing seems to be accomplished by a contraction and expansion of the ab- dominal segments. Nervous System.—The nervous system of insects is made up of a chain of ganglia that is connected by a double nervous cord, and occupies the ventral portion of the body. The portion above the oesophagus is called the cerebral ganglia. Fig. 112, m, shows the brain; and from here nerves pass to the various sense-organs. The ganglia below is called thoracic (Fig. 112, N), and sends nerves to the wings, legs, and other parts. Development. — Most insects are produced by eggs, while some appear The changes through which The butter-. Fig. 116.—Larva of insects. directly in the adult form the former pass are called metamorphoses flies, beetles, etc., pass through three changes from the egg to the perfect insect. The first stage is called the larva—grub, mag- got, or caterpillar (Fig. 116). In this form it is worm-like, has numbers of feet, eats voraciously, changes its skin (moults) frequent- ly, and finally in many instances spins a silken case or. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Holder, Charles Frederick, 1851-1915; Holder, Joseph Bassett, 1824-1888, joint author. New York : D. Appleton and company
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
