THE EVIDENCE OF THE AUDITORY APPARATUS 369 



It is especially noticeable that they do not exist in Galeodes or 

 in the scorpions, but in the former special sense-organs are found in 

 the shape of the so-called ' racquet-organs,' on the basal segments of 

 the most posterior pair of appendages, and also, according to Gaubert, 

 on the extremity of the palps and the first pair of feet, while in the 

 latter they occur in the shape of the pectens. 



This observation of Gaubert suggests that the place of the 

 lyriform organs in other arachnids is taken in- Galeodes by the 

 racquet-organs, and in the scorpions by the pectens. Bertkau, 

 Schimkewitsch, and Wagner, as quoted by Gaubert, all suggest that 

 the lyriform organs of the arachnids belong to the same group of 

 sense-organs as the porous chordotonal organs of the Insecta, sense- 

 organs which have been found in every group of Insecta, and are 

 generally regarded as auditory organs. Gaubert does not agree with 

 this, and considers the lyriform organs to be concerned with the 

 temperature-sense rather than with audition. 



The chordotonal organs of insects have been specially studied by 

 Graber. He divides them into two groups, the poriferous and the 

 non-poriferous, the former being characterized by the presence of 

 pores on the surface arranged in groups or lines. These poriferous 

 chordotonal organs are remarkably constant in position, being found 

 only at the base of the wings on the subcostal ridge, in marked 

 contrast to the other group of chordotonal organs which are found 

 chiefly on the appendages in various regions. The striking character 

 of this fixity of position of these organs and the universality of their 

 presence in the whole group, led Graber to the conclusion that in 

 these poriferous chordotonal organs we are studying a form of 

 auditory apparatus which characterized the ancestor of the insect- 

 group. These organs are always well developed on the hind wings, 

 and in the large group of Diptera the auditory apparatus has usurped 

 the whole of the function of the wing ; for the balancers or ' halteres,' 

 as they are called, are the sole representatives of the hind wings, and 

 they are usually considered to be of the nature of auditory organs. 

 It is instructive to find that such an auditory organ serves not only 

 for the purpose of audition, but also as an organ of equilibration ; 

 thus Lowne gives the evidence of various observers, and confirms it 

 himself, that removal of the balancers destroys the power of orderly 

 flight in the animal. 



A striking peculiarity of these organs in the Insecta, as described 



2 B 



