34 THE PHYSIOLOGY OF INSECT SENSES 



membrane can unfold imparts a mechanical component to adap- 

 tation. As he pointed out, this concept, while not explaining rates of 

 adaptation, brings it to another level of understanding. 

 All types of mechano -hairs studied (Wolbarsht and Dethier, 1958; 





7 — 



• } ■• 



Receptor Potential M V 



Fig. 24. Impulse size plotted against receptor potential for a mechano- 

 sensory hair on the second antennal joint of Melanopliis. All points 

 except lowest receptor potential are averages of at least twenty impulses. 

 Lowest value is a single impulse. Bars denote extreme values. (Redrawn 

 from Wolbarsht, 1960.) 



Wolbarsht, 1960; Pumphrey, 1936) appear to fall into two classes: 

 velocity sensitive and pressure sensitive. The former fire only while the 

 stimulus is changing. Some, such as the hairs on the leading edge of the 

 wings of flies and other insects (Wolbarsht and Dethier, 1958), may 

 fire at a rate of 600 or more impulses per second. Pressure-sensitive 

 hairs show a repetitive discharge during a static deformation. 



