INSECTS
heads and the protecting flaps beneath, and the sound comes out in perceptibly increased volume. There can be little doubt that the air chamber of the body and the ventral membranes are important accessories in the sound-producing apparatus. Living cicadas are often found with half or more of the abdomen broken off, leaving the air sac open to the exterior. Such individuals may vibrate the drumheads, but the sound produced is weak and entirely lacks the quality of that made by the perfect insect.
Wherever the periodical cicada appears in great numbers, the daily choruses of the males leave an impression long remembered in the neighborhood; and, curiously, the sound appears to become increasingly louder in retrospect, until, after the lapse of years, each hearer is convinced it was a deafening clamor that almost deprived him of his senses. Fortunately the cicadas are day-time performers and are seldom heard at night. The song of the periodical species has no resemblance to the shrill, undulating screech of the annual cicadas so common every summer in August and September. All the notes of the more common large form of the seventeen-year race are characterized by a burr sound, and at least four different utterances may be distinguished; the quality of three of the notes probably depends on the age of the individual insect, the fourth is an expression of fright or anger.
The simplest notes to be heard are sort purring sounds, generally made by solitary insects sitting low in the bushes, probably individuals that have but recently emerged from the ground. The next is a longer and louder note, characterized by a rougher burr, lasting about rive seconds, and always given a falling inflection at the close. This sound is the one popularly known as the "Pharaoh" song, because of a fancied resemblance to the name if the first syllable is sufficiently prolonged and the second allowed to drop off abruptly at the end. It
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