212 A NATURALIST IN HIMALAYA 



will reveal the presence of a pair of flat plates, each 

 about three-quarters of an inch in length, that cover 

 the anterior half of the under surface of the abdomen. 

 These plates are known as the opercula. They are in 

 reality prolongations backward of the hind segment of 

 the thorax ; they lie one on either side of the middle 

 line and are separated from the abdomen by a deep 

 narrow fissure. Hidden away within the base of either 

 operculum and stretched tightly across a hole in the side 

 of the first abdominal segment is a tense white mem- 



.Shield. 



'Operculum. 

 FIG. 7. Cicada (Platylomia brevis). 

 Wings on near side removed to show position of musical organs. 



brane, a structure of great importance in the production 

 of the sound. This is the tympanum or drum. In ap- 

 pearance it reminds one somewhat of the organ with a 

 similar name in the structure of the human ear. Im- 

 mediately above and overhanging the drum is a curved 

 plate that projects down from the first abdominal 

 segment. This is obviously designed to protect the 

 drum, and may be called the shield. These organs can 

 be seen by a simple inspection (Fig. 7). The remain- 

 ing two can be in a moment exposed. If with scissors 

 a small window is made in the under surface of the 

 abdomen of the cicada, it will be seen that the greater 

 part of the abdomen is nothing but a large air cavity 



