I n 1920, Hartridge advanced the proposition that bats detect and subsequently avoid obstacles by hearing reflections of high-pitched vocal sounds emitted during flight. Despite support offered by the experiments of Jurine (1798), Rollinat and Trouessart ( '00)' Hahn ( '08), and Griffin and Galambos ( '41), all of whom demonstrated that deaf bats avoid obstacles poorly; and by the evidence that bats emit supersonic sounds (Pierce and Griffin, '38), Hartridge's theory cannot pet be said to rest on the firmest experimental grounds. It is the aim of this paper to describe and analyze the cries of bats in the light of this theory.
The sounds emitted by four species of insect-eating bats have been studied with the aid of a microphone and amplifier system which detects sounds of frequencies between the extreme limits of about 100 and 75,000 cycles per second (.1 kc. and 75 kc.)2. The analyzer functions by converting the sound impinging upon the microphone into either ( a ) an audible sound of constant frequency issuing from a loudspeaker, or (b) a vertical excursion written on a moving strip of paper tape by an electromagnetic device. The analyzer, comnionly known as a supersonic detector because of its wide use for detection of sounds above the 20 kc. upper limit of the human l The species tested were Eptesicus fuscus fuseus, Myotis keenii septentrionalis, 2 F o r a complete description of this device, see the paper by A. Noyes and M. lucifugus lucifugus, Pipistrellus subflavus. G . W. Pierce ( '38).