Page:Insects - Their Ways and Means of Living.djvu/138



With the conditions of living granted, however, proto- plasm is still only potentially alive, for there is yet required a stimulus to set it into activity. The stimulus for lire activities comes from changes in the physical forms of energy that surround or infringe upon the potentially living substance; for, "live" matter, like all other matter, is subject to the law of inertia, which decrees that it must remain at rest until motion is imparted to it by other

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FIO. 66. The head and mouth parts of a grasshopper A, facial view of the head, showing the positions of the antennae (dnt), the large cornpound eyes (E), the slrnple eyes, or ocelli (O), the broad front lip, or labrum (Lin) suspended from the cranium by the clypeus (Clp), and the bases of the mandibles (Md, Md) closed behind the labrum B, the rnouth parts separated from the head in relative positions, seen from in front: Hphy, hypopharynx, or tongue, attached to base of labiurn; Lb, labiuml Lin, labrum; Md, mandibles; Mx, maxillae

motion. A very small degree of stimulating energy, how- ever, may result in the release of a great quantity of stored energy. The food of all living matter must contain carbon, hydrogen, nitrogen, and oxygen. The mechanism of plants enables them to take these elements from com- pounds dissolved in the water of the soli. Animais must get them from other living things, or from the products of

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