A preliminary version of this trial draft of a unit prepared for Australian secondary science students was previously announced as ED 049 931 under the short title of "Messengers." The teachers' guide is an overprinted version of the students' booklet, and lists objectives for each section of the materials, indicates possible teaching strategies, and lists the equipment needed for each activity. The core activities for all students contain three sections: (1) "Can You Always Believe What You See?" (optical illusions), (2) "How Sense"ible Are You?" (hearing acuity and directional resolution, optical resolution, angle of vision, optical near point, taste discrimination and sensitivity, touch discrimination, and reaction rate are determined and placed on a "sense profile"), and (3)"How Do the Senses Obtain Information?" (requirements for sound and light transmission, odors, and taste). Students choose one or more of the options: "How Sensitive are You?""Limits of Seeing,""How to be More Sense"ible" (use of artificial devices), "What is an Inference?""Other Senses" (inner ear and sense of position in space), and "Senses in Other Living Things." The students' booklet also contains self-administered diagnostic tests, with annotated answers. There is a student workbook. Some apparatus developed for the unit is not included in this package. (AL)