FUNCTIONS OF TYMPANAL ORGANS 151 



relieved of the fibres again responded normally, suggested that 

 the hairs are the receptors involved, as was found by the two 

 previously mentioned investigators. The results drawn from 

 foregoing experiments, with lepidopterous larvae, point to the 

 conclusion that these animals are sensitive to air currents and 

 to certain aerial vibrations. They obviously afford no evidence 

 that any sense of hearing in the anthropomorphic meaning is 

 involved, but lend support to the dictum already stated that, 

 in many insects, the tactile and auditory senses are very 

 questionably differentiated. No relation between the responses 

 mentioned and the segmentally arranged chordotonal sensillai, 

 known to occur in lepidopterous larvae, has been recorded, and 

 it appears improbable that they play any part in the process. 



There now remains for consideration the functions of tympanal 

 organs. It is noteworthy in this connection that in the saltatorial 

 Orthoptera, the Cicadidae and Corixidae, sound-producing organs 

 are present. This fact in itself suggests that if these sounds are of 

 significance in the lives of the species concerned, some type of 

 perceptor organs is necessary. In species devoid of any capacity 

 for sound-production tympanal organs are wanting : this happens, 

 for example, in the wingless Tettigoniidae and in the primitive 

 soundless genus Tettigarcta among the Cicadidae. That the 

 tympanal organs are auditory in function is supported by the 

 ingenious and controlled experiments of Baier (1930) with field 

 crickets and other Orthoptera. Individuals of species whose sexes 

 were segregated, and previously conditioned to a life in cages, were 

 placed in different rooms sufficiently distant to be beyond the 

 range of sound perception. A microphone, placed in the cage 

 containing the males, was connected by telephone with a receiver 

 in the cage containing females of the same species. The females 

 responded to the stridulation of the ^nales by orienting themselves 

 when they perceived the sound : this they did by approaching the 

 receiver with actively moving antennae and by performing move- 

 ments indicative of search for the summoning partners. When the 

 current was temporarily interrupted, the females may move away 

 from the receiver, and in any case no longer betray their former 

 signs of attention. On restoring the circuit the females at once 



