Abstract
Various types and degrees of asymmetry of ears in owls have been studied by Pycraft as earlyas in 1898 (also 1910). But, this interesting adaptive feature seems to have not been reexamined, except recently illustrated by Payne (1967) in Tyto. Here, remarkable type of asymmetry in Asiof lammeus is confirmed by photographs. Although the skull is symmetric in basic structure as Pycraftstated, a minor asymmetry could be found in more protruded squamosal wing on the right side, andperhaps compensatory slight reduction of post-orbital process of the same side was noticed. Thefacial discs can be most extensively turned over in Asio among owls. Ninox for example, has nofacial disc opercula and has normal symmetric external ears. It is to be noticed that different typesof asymmetry revealed in owls may be taken as an example of random adaptations established bynatural selection. The sygnificance of ear asymmetry for sound orientation has been discussed byPumphrey (1948), and the comparative development of the facial discs is considered in relation tohabit by Grossman & Hamlet (1965).
