INTERNAL STRUCTURE OF THE GRASSHOPPER. 265 



3. On that side which is not surrounded by the rim the 

 tympanum is continuous with the ordinary integument. 



4. On this side notice the spiracle (cf), and, below this, 

 the auditory nerve (I) passing from the third thoracic 

 ganglion to the ear. 



Fio. 140. 



FIG. 140. Left auditory organ of a grasshopper (Stenobothrus rufus), 

 viewed from within and magnified about ten diameters. This figure is a 

 combination of three of the figures given by Oscar Schmidt (Die Gehor- 

 organe der Heuschrecken, Arch. f. Mih. Anat. xi. 195, 1875). 



a. Thickened margin of the tympanum, b. The tympanum, c. Mus- 

 cles, d. Spiracle, e. Cone-shaped prominence, g. Its lateral prolon- 

 gation, f/'. Thickened fold of the tympanum. /;. Tube leading to the 

 triangular chamber, k. Triangular chamber. L Small ganglion. I. Au- 

 ditory nerve, m. Auditory ganglion. 



5. A number of small muscles (c, c) are attached to the 

 free ends of the run, and are so arranged that when they 

 are contracted the tension of the tympanum is diminished. 



6. That side of the tympanum which is nearest the 



