INSECT VARIETY. 235 



produce the sound. De Geer^ in Sweden, speaking of the 

 Migratory Locust, says : — " On each side of the first segment 

 of the abdomen immediately above the origin of the posterior 

 thighs, there is a considerable and deep aperture of rather an 

 oval form (see a, Fig. 3, Plate II.), which is partly closed by 

 an irregular flat plate or operculum of a hard substance, but 

 covered by a wrinkled flexible membrane. The opening left by 

 this operculum is semi-lunar, and at the bottom of the cavity 

 is a white membrane of considerable tension and shining like a 

 mirror. On that side of the aperture towards the head there is 

 a little oval hole (e. Fig. 1b), into which the point of a pin 

 may be introduced without resistance. When the pellicle is 

 removed, a large cavity appears. In my opinion this aperture, 

 cavity, and above all the membrane in tension, contribute much 

 to produce and augment the sound emitted by the grasshopper." 

 These authors are followed by Latreille and Burmeister. The 

 latter sought anatomically here to find a reason for the music as 

 follows : — On the delicate (drum) skin, near the front margin, 

 he says, lies a small brown horny piece, to which inwardly a 

 fine muscle is inserted that runs over to a projection of the outer 

 horny band above and in front of the margins of the skin. By 

 means of this small muscle, when the swift movements of the 

 hind legs set the skin with the body into vibration, it con- 

 sequently sounds. 



In contradiction to the preceding, the celebrated Johannes 

 Miiller, in a supplement to his often-quoted paper on " The 

 Visual Organs of Insects," published in 18£9, having first 

 shown the drumskin membranes to be in direct connection with 

 the nervous chord, postulates their function to be auditory. 

 He finds this membrane '^ of an almost rhomboidal shape 

 in Gryllus, now PcEcilocerus Jneroglj/phiciis, five lines wide, 

 smaller in the males, and nowhere perforated or broken by the 

 smallest fiaw. When the insect retains its wings in the position 

 of repose, this part is quite covered by the elytra. At the inner 

 surface of this membrane lies a very delicately-skinned bladder 

 filled with water, elongate, and over two lines in length, covering 

 the membrane with one extremity, and with the other directed 

 downwards (Plate II., Fig. 1b ; Plate VI., Fig. 2) . This bladder 

 (Miiller^s ganglion) must be plainly distinguished from the 



