POSITION OF AUDITOEY RODS. 113 



in other parts of the body ; for instance, they have been 

 discovered in the antennae of a water-beetle (Dytiscus) 

 and of Telephorus by Hicks, Leydig, and Graber, and in 

 the body segments of several larvse by Leydig, Weiss- 

 mann, Graber, Grobben, and BoUes Lee, In the larva 

 of Dytiscus, indeed, they have been observed in the 

 body, antennae, palpi, under lip, and legs. Moreover, 

 while, as we have seen, in the tibias of Orthoptera 

 and the halteres of flies they are numerous, in some of 

 these cases they are few, sometimes, indeed, only a 

 single rod being present, as discovered by Grobben in 

 Ptychoptera.* Nevertheless the evidence that they 

 are really acoustic organs is, in the case of the 

 Orthoptera, so strong, their structure is so peculiar, 

 and the gradation of these organs from the most com- 

 plex to the most simple is so complete, that it seems 

 reasonable to attribute to them the same function. 



Moreover, as regards the very simplest forms there is 

 another consideration pointing to this conclusion. We 

 have seen that in the Orthoptera the terminal filaments 

 close up, and are attached to the skin. Now, it seems 

 to be a very general rule, in reference to these organs, 

 that they are attached to the skin at two points, 

 between which is situated the attachment of the nerve. 

 These points, moreover, are so selected as to be main- 

 tained at the same distance from one another, thus pre- 

 serving an equable tension in the connecting filament. 



Fig. 72, for instance, represents part of one segment 

 of the body of the larva of a gnat (Corethra). This larva 

 is as transparent as glass, and very common in ponds, 

 a most beautiful and instructive microscopic object. 

 EG is the ganglion ; a is the nerve in question, which 



* Sitz. der K. Akad. der Wiss. Wien, 1876. 



