An apparatus is described "constructed in such a way that the initial reaction of a series automatically brings about the manipulandum which as a stimulus evokes the second reaction, the second reaction automatically brings about the presentation of the manipulandum which as a stimulus evokes the third reaction, and so on." The apparatus is designed for use with rats, and consists essentially of the various bars and a chain used as manipulanda, mounted on a carriage, and a retaining box which gives the subject access to the manipulanda in a serial order. The apparatus is illustrated schematically and instructions for its construction are included. (PsycINFO Database Record (c) 2006 APA, all rights reserved)