1975] 
Willey — Sound Production in Arphia 
339 
phase shift is caused by the necessity of the femoro-tibial joints to 
overlap the mid-point of the dorsum in order to produce enough 
pressure on the file. Functionally, it is postulated that this system 
produces a frequency modulation which allows an FM signal of 
^ IO KHz to be pulsed periodically during the downstroke — a 
frequency long ago proved to be also at the greatest sensitivity of 
the tympanal receptor of this species. 
Acknowledgements 
I thank Howard Johnson (Visual Data Systems, Inc.) and Prof, 
Walter Bock (Columbia University) for their help and encourage- 
ment, and Gerry Temaner (University of Illinois Office of Instruc- 
tional Resources) for his suggestions about proper duplication of 
valuable original sequences. Ronald Weibel was the technologist 
for the scanning electron microscope study and Ronald Walkosz, 
David Mucha and Dr. R. L. Willey helped prepare the plates for 
publication. Joan Bieler, Allan Johnson, Mrs. June Steinberg and 
Luis Jiminez helped in the recording of measurements. David Bal- 
lestas and Luis Jiminez (Federal Work-Study Program) cared for 
the cultures. This study was supported partly by grants from the 
University of Illinois Research Board and the Department of Bio- 
logical Sciences by the kindnesses of Professors J. O. Corliss and 
E. B. Hadley, former Department Heads. Publication was aided 
by an NSF grant GB-35594 to RBW. 
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