92 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



presents an enlarged oval area (b), which corresponds with the area 

 of the sound-producing cymbal of the male. 



The sternal plates of the first and second abdominal segments are 

 highly modified, and they are separated by a deep inflection that forms 

 a large ventral cavity at the base of the abdomen. This cavity is 

 ordinarily closed to a narrow slit between the sternal plates, and is 



IT IIT 



Fig. 30. — Abdomen of Magicicada scptcndccim (Cicadidae). 



A, entire abdomen and base of thorax of adult female. 



B, details of connection between thorax and abdomen, lateral view. 



C, ventral plates of metathorax and first and second abdominal segments. 



D, base of abdomen of mature nymph. 



E, tenth and eleventh segments of adult. 



a, hinge between postnotum of metathorax and first abdominal tergum ; bj 

 lateral area of first abdominal tergum on which cymbal of male is developed; 

 c, lateral arm of first abdominal sternum with expanded end (d) on which tergo- 

 sternal muscle is attached ; e, posterior median plate of first sternum ; /, anterior 

 median plate of second sternum ; g, lateral arm of second sternum forming 

 marginal rim of tympanum {Tin). 



but little evident in a casual examination of a dried specimen. In the 

 male cicada the cavity is much larger than in the feinale and contains 

 the so-called " resonance " membranes, or " mirrors ", which are 

 now regarded as tympana for the reception of sound vibrations, since 

 it has been shown by Vogel (1923) that chordotonal organs, situated 

 in the lower ends of the second abdominal tergum, are connected with 

 their lateral extremities. The tympanal cavity can be opened and 



