Located in the forelegs, katydid ears are unique among arthropods in having outer, middle, and inner components, analogous to the mammalian ear. Unlike mammals, sound is received externally via two tympanic membranes in each ear and internally via a narrow ear canal (EC) derived from the respiratory tracheal system. Inside the EC, sound travels slower than in free air, causing temporal and pressure differences between external and internal inputs. The delay was suspected to arise as a consequence of the narrowing EC geometry. If true, a reduction in sound velocity should persist independently of the gas composition in the EC (e.g., air, CO2). Integrating laser Doppler vibrometry, microcomputed tomography, and numerical analysis on precise three-dimensional geometries of each experimental animal EC, we demonstrate that the narrowing radius of the EC is the main factor reducing sound velocity. Both experimental and numerical data also show that sound velocity is reduced further when excess CO2 fills the EC. Likewise, the EC bifurcates at the tympanal level (one branch for each tympanic membrane), creating two additional narrow internal sound paths and imposing different sound velocities for each tympanic membrane. Therefore, external and internal inputs total to four sound paths for each ear (only one for the human ear). Research paths and implication of findings in avian directional hearing are discussed.

katydid 耳朵位于前腿，在节肢动物中是独一无二的，它具有外部、中间和内部组件，类似于哺乳动物的耳朵。与哺乳动物不同，声音是通过每只耳朵的两个鼓膜从外部接收的，内部通过来自呼吸气管系统的狭窄耳道 (EC) 接收。在 EC 内部，声音的传播速度比在自由空气中慢，导致外部和内部输入之间存在时间和压力差异。延迟被怀疑是由于 EC 几何形状变窄而引起的。如果为真，声速的降低应该独立于 EC 中的气体成分（例如，空气、C哦2）。结合激光多普勒振动测量、显微计算机断层扫描和对每个实验动物 EC 的精确三维几何结构的数值分析，我们证明了 EC 的缩小半径是降低声速的主要因素。实验和数值数据还表明，当过量时声速会进一步降低。C哦2填充 EC。同样，EC 在鼓膜水平分叉（每个鼓膜一个分支），创建两个额外的狭窄内部声音路径并为每个鼓膜施加不同的声速。因此，每只耳朵的外部和内部输入总共有四个声音路径（人耳只有一个）。讨论了鸟类定向听力的研究路径和研究结果的意义。