Upon completion of organ formation and histogenesis, the embryo begins to stretch and contract its newly formed muscles, and gas is secreted into the trachea. Embryogenesis is over when the maternally supplied yolk has been consumed. Hatching is achieved by any number of means, but typically, hatching is a mechanical process, in which the larva either chews its way out of the chorion, grows by imbibing air until the chorion cracks, or uses a special egg burster. There is sometimes an enzymatic digestion of the eggshell, but complicated hydrostatic mechanisms are used, as well. The hatchling emerges as a first instar (larva or nymph).

See Also the Following Articles

Eggs • Imaginal Discs • Segmentation • Vitellogenesis

Further Reading

Cohen, S., and Juergens, G. (1989). Proximal—distal pattern formation in Drosophila: Graded requirement for Distal-less gene activity during limb development. Roux's Arch. Dev. Biol. 198, 157—169. Counce, S. J., and Waddington, C. H. (1972). "Developmental Systems:

Insects," Vol. 2. Academic Press, London. Hegner, R. W. (1911). Experiments with Chrysomelid beetles. III: The effects of killing parts of the eggs of Leptinotarsa decemlineata. Biol. Bull. 20, 237-251 (1911). Kume, M., and Dan, K. (1968). "Invertebrate Embryology." Garland

Publishing, New York. Nusslein-Volhard, C., and Wieschaus, E. (1980). Mutations affecting segment number and polarity in Drosophila. Nature 287, 795-801. Lewis, E. B. (1978). A gene complex controlling segmentation in

Drosophila. Nature 276, 565-570. Sander, K. (1976). Specification of the basic body pattern in insect embryogenesis. Adv. Insect Physiol. 12, 125-238. Sander, K., Gutzeit, H. O., and Jaeckle, H. (1985). Insect embryogenesis: Morphology, physiology, genetical, and molecular aspects. In "Comprehensive Insect Physiology, Biochemistry, and Pharmacology." (G. A. Kerkut and L. I. Gilbert, eds.). Pergamon Press, Oxford, U.K.

Scott Hoffman Black and Mace Vaughan

The Xerces Society

The Xerces blue butterfly, Antioch katydid, Tobias' caddisfly, Roberts's alloperlan stonefly, Colorado burrowing mayfly, and Rocky Mountain grasshopper all were driven extinct by humans, and all foreshadow the fate of the world's endangered insects. With almost 1 million described species, insects eclipse all other forms of animal life on Earth, not only in sheer numbers, diversity, and biomass, but also in their importance to functioning ecosystems. However, human-induced changes to the natural environment endanger vast numbers of these organisms, threatening them and the vital services they provide with extinction.

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