Most terrestial insects orient themselves through vision, and most of them take advantage of the direction of light rays. Although other factors may influence the direction in which a given individual will travel, the visual, and possibly the olfactory, senses seem to be those chiefly utilized in maintaining a direct path. The only studies of a complete nature relating to this phenomenon in aquatic insects were made by Holmes (1905). In the following experiments, the larvm of Anax junius and

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... e species of Aeschna were employed. Two larvm were taken from the water, and the left eye of one insect and the right eye ot the other covered with asphaltum. As soon as the asphaltum hardened they were put back into the water for about an hour. They were then removed and placed on a sheet of white paper. Their courses were traced with a pencil as they crawled. Ten such tracings were taken at one time; the animal was then placed in the water and allowed to rest. Thirty tracings in all, were taken for each of the two insects. The animal always turned toward the side with the covered eye. Often, after a few trials, the paths were almost straight; showing that habit tended to overcome the turning. These experiments were conducted in diffuse daylight. Other experiments were tried with a beam from a 500 watt bulb. A larva with the left eye covered was placed at right angles to the beam and to the left of its source. In twenty-one trials it turned five times to the left, eight to the right, four times it followed a straight course, and finally turned four times to the right. On the, following evening it turned seven times to the left, eighteen times to the right, once it took an irregular course, and once turned to the right. Two evenings later it first followed a straight course once, turned six times to the left, once followed a straight course, and finally turned seven times to the right. On the same evening, this insect was tried facing the light. Once it followed a