VI ANTENNATA—SOUND-PRODUGING APPARATUS 483 



apneustic. The tracheal gills, according to all observers, are respiratory 

 organs, which have arisen independently of each other in various 

 insect orders as adaptations to aquatic life. They are thrown off 



Fig. 342. — Epliemerid larva witli two 

 tracheal gills on eacli side of each, ab- 

 dominal segment, and with 3 caudal pro- 

 cesses (oerci) (after E. Leuckart). 



Fig. 343. — Eight half of the middle 

 abdominal segment of the larva of Baetis 

 (Chloe) binooulatus with tracheal gills (after 

 Palmen). trl, Longitudinal tracheal trunks ; 

 vf, strand like threads of attachment of the 

 longitudinal trunks to the integument (stig- 

 matic strands) ; Izir, gill trachea ; (rfc, tracheal 

 gills. 



during the transition to the imaginal form in the Epliemeridce, Agrionidx, 

 and Diptera, but are retained in the imagines of the Perlidw, jEschnida, 

 SialidcB, Lepidoptera, and Ooleoptera. 



X. Sound -Producing Apparatus. 



It is well known that many insects can produce sounds. These 

 sounds, which play many different parts in insect life, are principally 

 produced — 



1. By rapid vibrations of the wings {Hymenoptera, Dipfera), and 

 by the vibration of the halteres against the alulae (Diptera). 



2. By the vibration of leaf-like appendages in the tracheae. 

 These often lie in great numbers near the stigmata, and are made to 

 vibrate during the respiratory movements of the animal by the inward 

 and outward streaming of the air (Hymenoptera, Biptera). 



3. By the rubbing together of rough uneven portions of the 

 integument The Acrididce stridulate by scraping their posterior femur 



