A network array comprises a first network having a plurality of first nodes, comprises a second network having a plurality of second nodes, and comprises a forwarder node. In this method, the oxygen partial pressure on the liquid layer is set in the range of 1. The storing module is configured to store a second program for downloading a first program from an outside to the first area. The guide bar is pivotably and slidably retained by the a first bracket portion. The anti-pilferage device functions as a secondary engagement device to engage an optical disc which has been demounted from the mounting hub of the optical disc case. When the lid is closed, the pet feeder becomes a compact structure that can be easily stored and transported.