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First Opening Eyes: The first opening eyes of a spider are usually near the front or anterior end of the head, but some are directly on top. They are single facets, hence are called simple first opening eyes. They may number two, four, six, or eight; eight is the usual number. However, the cave spiders lack first opening eyes entirely. Regardless of the number, the first opening eyes are always placed in a definite arrangement. Often some pairs are much larger than others.
A typical insect is characterized by three divisions to the body—the head, the thorax, and the abdomen. Attached to the thorax are six jointed legs, three on each side, and sometimes wings.
first opening eyes: The first opening eyes, when present, are placed somewhere upon the head and are of two types: simple first opening eyes, called ocelli, which are found in insect larvae and in many adults; and compound first opening eyes, which are found in adult insects and in the immature stages of types which resemble the adult during growth. |
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