ZOOLOGY. 443 



cept when attacked, alarmed, or irritated. Landois also be- 

 lieves that insect sounds serve as means of mutual commu- 

 nication and understanding upon subjects not immediately 

 connected with sexual instincts. In PoggendorfP s Annalen, 

 vol. cl., Landois has published a long series of experiments, 

 accompanied by phototypes from photographs of a number 

 of sound-lines, produced by drawing a penknife over the sur- 

 face of a highly polished plate of metal or glass. Now, the 

 phenomena of friction sounds and tones in the Articulata are 

 exactly analogous. In crabs, spiders, beetles, crickets, etc., 

 the fine notches which are found on their various file- or rasp- 

 like organs correspond with the marks on the sound-lines of 

 the plates experimented upon ; and over these file-notched 

 organs some sharp edge, belonging to some other part of the 

 body, is moved backwards and forwards. The tone pro- 

 duced bears exact relation to the fineness of the notches and 

 the rapidity with which the moving part of the apparatus is 

 driven. It is observed, for instance, that when the move- 

 ments of the thighs of the grasshoppers begin rather slowly, 

 the "srr" tone is deeper than when the motion is more 

 rapid ; and the finer the notches, or the more rapid the 

 movements, so much more acute are the tones given out by 

 the crickets, beetles, bugs, etc. 



If the number of notches and the length of the file be 

 known, and also the time occupied by the movement of the 

 organs, the pitch of the tone produced by the insect can be 

 easily reckoned. And, conversely, other known quantities 

 may be found as, e. (/., the number of notches on the file can 

 be reckoned from the data of pitch of tone, length of file, and 

 time of motion. 



We can thus obtain some idea of the notes of insects whose 

 fossil remains still show the length of the notched ridges and 

 number of notches thereon, if we assume the movement of 

 the parts to have the same rapidity as is observed in living 

 species ! 



To determine the note of a free-flying insect requires a 

 very musical ear, and also long practice in recognizing and 

 distinguishing the note sounded by an insect flying rapidly 

 b} r , as any one will find who tries. When the sexes of the 

 same species differ much in size, so does the wing-tone. 



A certain small bee gives the tone A, while the much larger 



