Although elaborate instrumentation is not re­ quired for good research in comparative psy­ chology, the manipulation, control, and mea­ surement of variables in the study of animal behavior has frequently been facilitated by ad­ vances in technology and the invention of ap­ paratus. Instrumentation serves to increase the precision of measurements and to standardize tests procedures, which in turn facilitates com­ parable research methods across species and across laboratories. Developments in apparatus can also open completely new lines of inquiry, fostering questions that could not have previ­ ously been addressed and, occasionally, chal­ lenging findings established in previous re­ search. Revolutions in science have frequently accompanied major developments in apparatus such as the invention of the microscope and the telescope. What instruments will be remem­ bered as being revolutionary in the history of comparative psychology?