Organisms that have this ability possess a specialized leading digit known as an alula. Animals that have lost this ability tend to have symmetrical remiges (“re-MEE-jez”). Echelon formations are adopted by groups of organisms with this ability. Structures that confer this ability are categorized as primary or secondary, and can include small serrations to reduce noise. Tree-down and ground-up are two theories for the evolution of this ability, (10[2])seen in the transition species Archaeopteryx (10[1]-5[1])(“arch-ee-op-te-rix”). Organisms (10[1])with this (10[1])ability have hollow bones. For 10 points, name this ability to generate lift (10[1])in the air possessed by animals like birds. ■END■