5. Although the aquatic larva is preparing for adult life in the air, there should be some arrangement for securing air in the water. Where do you find outgrowths of the skin which might increase the air-absorbing surface? How many of these structures are there? Look within them for the air tubes,--fine branching black lines. 6. If possible, without injury to the specimen, examine the larva's mouth. Try to discover how it is used and how it is protected when not in use. _Suggested drawings._ a. The entire larva, × 4. b. A gill, as seen through the microscope. c. The feeding apparatus, × 10. PLANT LICE AND SCALE BUGS Plant Lice (Aphids) _Materials._ Plant lice on various kinds of plants, such as house plants, golden glow, and other plants from the garden or field. Garden asters with root lice (the asters should be transplanted into pots). _Observations._ 1. Describe the size, appearance, and colors of the plant lice in your collection and their relation to the host plant. 2. Are the lice active or sluggish? (Compare with a house fly, for instance.) What proportion of them have wings? What is the usual method of locomotion? 3. Examining a single winged specimen, how many wings do you find? How do they fold? What is the character of the wings? 4. What is the food of the plant lice? How is the food obtained? (With a hand lens identify the piercing organ.) On what parts of the plants are they found? Does the plant show any indication of being harmed by the lice? If so, how? 5. Make a count of the plant lice upon a portion of a plant and estimate the whole number upon a plant. Why are plant lice a very serious pest? 6. If any plant lice have ants associated with them, study the behavior of the ants in this curious relationship. What advantages result from this relationship of ant and aphis to either or both insects? Scale Bugs _Materials._ Twigs of trees, leaves, fruit, ferns, etc., infested with these bugs. If possible, have samples of San José scales, maple scales, and oyster scales. _Observations._ 1. What is the general size and appearance of the various scale bugs in your collection? How do they differ in form and size and color? 2. Remove a scale and study it carefully with a lens. What is under the scale? Of what is the scale composed? What do you discover about these bugs to indicate that they are really insects? 3. What can be said about the number of scale bugs? Why are they difficult to exterminate? How can they be distributed from one place to another, as from orchard to orchard, since only the males have wings? _Drawings suggested._ a. A single aphis as seen with hand lens. b. Various scale bugs as seen with a hand lens. c. Twigs showing the distribution and numbers of scale bugs. WATER BUGS AND BEETLES Water Bugs _Materials._ Water bugs and beetles of several species in small aquaria covered with a wire net. _Observations._