INSECT VARIETY. 233 



to those of the musical tymbal^ but more delicate. This^ how- 

 evei'j is no peculiarity. 



Towards the outer angle of the mirroris a brown and chitineous 

 styliform discoloration (m), translucent, thickened at its edges by 

 a sei'rated line of tubercles, attenuated, slightly angulated, with 

 its point tangential to the iridescent central spot, and its opposite 

 extremity directed towards another callosity [m') similarly tuber- 

 culated, situated on the edge of the membrane of the mirror, 

 triangular in shape, and near its angle. The two chitineous 

 pieces nevertheless are not in contact, but by transmitted light 

 appear connected by a slight {nervous) thread. They are neither 

 constant in the species in number or shape ; for in the female 

 Cicada of the Ash there are two styliform pieces inclined at an 

 angle ; one traverses the iridescent spot, the other separates it 

 from the opaque portion of the membrane. Generally these 

 chitineous pieces harmonise with those in the corresponding 

 membranes of the grasshopper and moths [Trommelfellkorpchen). 



The nervous system of the drumming Cicadidse, consisting of 

 double chords frequently coalescing in the thorax, presents 

 different aspects in the various species. For example, in the 

 female of the Classic Plebeja, the ganglia formed by the uniting 

 of the chords in the prothorax and mesothorax are contiguous ; and 

 from the latter (/) the [acoustic) nerve connected with the mirror 

 is symmetrically given off (Plate VII., Fig. 1, n). In the 

 male sex it is most obvious; here it may be easily traced round 

 the motor muscle of the tymbal to the apical angle of the frame, 

 within which it forms a ganglion that enters a groove. The 

 other end of this groove lies towards the callosity m, and here 

 a yellowish cord may be traced from the outer wall of the mirror 

 to the tracheal pipe {t) of the first abdominal spiracle ; in the 

 male Plebeja this is free, but in the Blood Cicada it lies along the 

 edge of the mirror. This nervous cord likewise passes over or 

 surrounds the triangular callosity m. In the females of these 

 European species the arrangement is different, however, and the 

 ganglion does not lie within the frame. Of the several 

 parts of insect auditory organs, recognised by German 

 authors, I reserve description of Muller^s ganglion, which should 

 be represented by the portion of the acoustic nerve lying on the 

 callosity m. 



