2 86 ORTHOPTERA 



CHAP. 



muscles, and tracheal apparatus of a complex nature ; it is no 

 doubt delicately sensitive to some forms of vibration. Unlike 

 the stridulating organ, these ears exist in both sexes ; they are 

 found in a great majority of the species of Acridiidae. The 

 forms in which the ears are absent are usually at the same time 

 wingless and destitute of organs of stridulation ; but, on the other 

 hand, there are species some of them wingless that are, so far 

 as is known, incapable of stridulation and yet possess these ears. 



It is, indeed, a matter of great difficulty to decide as to the 

 exact function of these ear-like acoustic organs, which, we may 

 remind the reader, are peculiar to the saltatorial Orthoptera, and 

 we must refer for a full discussion of the subject to Graber's 

 masterly works,-^ contenting ourselves with a brief outline, which 

 we may commence by saying that the Orthoptera with ears are 

 believed to be sensitive to sounds by means other than these 

 organs. This suggests that the latter exist for some purpose 

 of perception of special sound. But if so what can this be ? 

 Only the males possess, so far as we know, effective sound- 

 producing organs, but both sexes have the special ears : more- 

 over, these structures are present in numerous species where 

 we do not know of the existence of phonetic organs in either 

 sex. Thus it appears at present impossible to accept these 

 organs as being certainly special structures for the perception 

 of the music of the species. It is generally thought that the 

 females are charmed by the music of the males, and that these 

 are stimulated to rivalry by the production of the sounds ; and 

 Dufour ^ has suggested that this process reacts on the physio- 

 logical processes of the individual. There has not been a sufficient 

 amount of observation to justify us in accepting these views, and 

 they do not in any way dispose of the difficulty arising from the 

 existence of the acoustic organs in species that do not, so far as 

 we know, produce special sounds. It is possible that the solution 

 of the difficulty may be found in the fact that these apparently 

 dumb species do really produce some sound, though we are quite 

 ignorant as to their doing so. It is well known that sounds 

 inaudible to some human ears are perfectly distinct to others. 

 Tyndall, in his work on Sound, has illustrated this by a fact that 

 is of special interest from. our present point of view. " Crossing 



^ Denk. Ak. JVieu, xxxvi. 1875 ; Arch. mikr. Anat. xx. and xxi., 1882. 

 - Mem. Ac. Sci. Strang, vii. 1834, p. 306. 



