WERNER MARCHAND 43 



Paoli, in seeking for the function of this organ, recalls his own 

 observation of the larvae producing a crackling noise, under water 

 as well as in the air, similar to the sound produced by small electric 

 discharges. He thinks that these sounds might be produced by- 

 means of this organ. By the action of the muscles the cyst would 

 be subjected to deformations by means of which the pedunculate 

 bodies would be caused to hit against one another. The elastic 

 membranes also would aid in this process as well as the chitinous walls 

 of the capsule. The two large tracheae would serve as resonators. 



The objection that such an organ of sound should lie at the surface 

 of the body rather than in its interior, is met with the consideration 

 that these larvas are aquatic, living below the surface of the water 

 or in the mud, where the possession of an organ producing sound in 

 the air would be of little value. The song of the Cicada becomes 

 much feebler when the insect is submerged under water, but the 

 larva in question produces its sound as well under the water as in 

 the air. As the pedunculate bodies are enclosed in a liquid, the con- 

 duction of the sound would also occur easily in a liquid element. If 

 the peculiar sound produced by the larva was not caused by the action 

 of this organ, there would be, according to Paoli, no other organ by 

 which it could possibly be produced. Paoli has consequently de- 

 cided to assign to the organ a sound-producing function.^ 



^ I have in the meantime found occasion to observe tabanid larvas, and was 

 eager to test Paoli's observations. In fact the crackling noise was freely produced 

 by full grown Tabanus atratus larvai, and also, in harmony with Paoli's state- 

 ment, it was chiefly heard when the larvae were disturbed and defending them- 

 selves with their sharp mandibles. The coincidence of the two phenomena was 

 so close that I am bound to assume that the sound is produced by means of the 

 mandibles. As is well known, the mandibles of tabanid larvae are strongly chit- 

 inized and provided with a serrate inner edge. Very near this and slightly be- 

 low, the maxillae, also chitinous, are situated. In the act of biting, the mandibles 

 are suddenly exserted with considerable force and it is conceivable that in this 

 act their serrate edge strikes the maxillae, producing a sharp sound. The action 

 itself may have some physiological importance, in as far as it serves in the lacera- 

 tion of the skin or body wall of animals attacked, while the sound produced ap- 

 pears to me more accidental, as, for instance, the gnashing of teeth in carnivora. 

 Hence it is not likely that Graber's organ has the function ascribed to it by 

 Paoli. Also Paoli's opposition to Graber's view is not well founded in as far as 

 he himself assumes that the pedunculate bodies are modified hairs. They could 



