The author had laid before the Society, on the 19th January, a preliminary note containing an outline of a theory of the function of the semicircular canals of the internal ear. In that note it was stated that the six semicircular canals form three pairs—the members of each pair being parallel, and having their ampullæ at opposite ends. In this paper the author communicates the results of measurements of the position of the bony canals in a large number of animals.