Choose Show Hidden Objects from the View menu.
Choosing the command a second time again reverses the toggle (from shown to hidden and back again).
The criterion for hiding or showing a file or folder is based on its data type. Use the Set Filter Options command to change which data types are shown and hidden. (See "To Specify Which Data Types Are Hidden" below.) The default hidden data types are DOT_FILE, DOT_FOLDER, and CURRENT_FOLDER.