152 THE SENSE ORGANS AND REFLEX BEHAVIOUR 



approached the receiver again. The cages, it may be added, were 

 insulated so as to guard against soHd vibrational stimulation. 

 None of the responses came from females whose tympana were 

 excised, and a local anaesthetic (ethyl chloride) applied to these 

 organs had only the same effect just so long as its influence lasted, 

 normal response being ultimately restored. The use of gramo- 

 phone records of the male stridulatory notes had an effect similar 

 to that exercised by the living insects themselves. 



In their investigation of auditory responses in Locusta, 

 Pumphrey and Rawdon-Smith (1936) deny any ability on the 

 part of this insect to discriminate frequency of vibrations by 

 means of its tympanic organ. They find no differentiation of 

 nervous response for different frequencies of stimulus and conclude 

 that the physical structure of the tympanal organ is such as would 

 not permit of discrimination of frequency by means of a 

 differentially resonant mechanism. They remark, however, that 

 the organ is well adapted to enable the insect to localise the 

 source of a sound whose frequency falls within its auditory 

 spectrum, e.g., the stridulation of another locust. The organ 

 resembles the human ear only in its relatively greater sensitivity 

 to the higher frequencies of sound waves. On this subject 

 references should also be made to the paper by Wever and 

 Bray (1933), which deals with nerve impulses originating in the 

 tympanal organs of crickets and katydids. These organs respond 

 to sound frequencies of from 250 to over 11,000 vibrations per 

 second : the quality of the response was found not to vary with 

 the frequency. Myers (1929) has collected a large amount of 

 circumstantial evidence relative to the " songs " of Cicadas and 

 their significance. The primary function of the notes of these 

 insects, according to this observer, is an assembling one, and it 

 may also serve to arouse the necessary stimulus leading to the 

 consummation of the sexual act. There does not appear to be 

 any conclusive experimental evidence with regard to sound 

 perception in these insects, but anatomical and observational 

 data, relating to their behaviour, appear to offer little reason to 

 doubt the auditory functions of their tympanal organs. The 

 tympanal organs of Lepidoptera likewise appear to be organs for 



