[Basic analysis of the effective system of homing in spider Agelena labyrinthica (Cl.)].

1. The spider Agelena labyrinthica Cl. determined its home direction by integrating the information of each element of the outgoing path to the prey in continuous interaction with the incident light. 2. A vector hypothesis explaining how the direction and the length of the homing track was determined was verified: if the azimuth of the incident light was displaced by 90 degrees as soon as the spider had reached a certain point on the web, the vector of the theoretical course originating from this point was rotated by about 60 degrees. The end point of this rotated vector ("fictitious retreat point") was not only the goal for the homing course from this point, but also for the course originating from any other point of the web. 3. Spiders starting at the fictitious retreat point did not keep straight courses. Their movements were either at random or they were directed in slightly preferred directions caused by the phototactic influence of the previously performed outward course. 4. If the light had been displaced before the spider was lifted from the web, the lifting had no effect on the orientation performance. 5. The mean distance between the points of direction changes and the starting points varied linearly with the mean length of the outward course; therefore these distances were used as an indication for the distance orientation. 6. Contrary to all other formerly published hypotheses on the photomenotactic orientation of arthropods MITTELSTAEDTs' hypothesis about the homing of Agelena, which is similar to my vector hypothesis, is compatible with the data compiled by this investigation.