52 



THE PHYSIOLOGY OF INSECT SENSES 



Chordotonal Sensilla 



Cord-like sensilla devoid of a specialized exocuticular component 

 and stretching from one point of the body wall or its derivatives to 

 another are peculiar to insects and have been found in every species 

 in which they have been sought (Siebold, 1844; Leydig, 1851 ; Graber, 

 1882a, 1882b; Eggers, 1924, 1928; Snodgrass, 1926; Debaisieux, 



Fig. 43. Diagrams to illustrate probable alterations in tension of the three 

 stretch receptors of Aeschna larvae. A (inspiration) and B (expiration) 

 show the movements of the sternal and pleural regions of the body 

 wall during ventilation. Upper figures, dorso-ventral muscles. Lower 

 figure, oblique receptor of right side. The oblique receptor will be 

 stretched during A and relaxed during B. C and D illustrate probable 

 effects of longitudinal movement on longitudinal and vertical re- 

 ceptors. (Redrawn from Finlayson and Lowenstein, 1958.) 



1935, 1938 ; Debauche, 1935; and others). They are widely distributed 

 in the body. In all insects they occur in the appendages of the mouth 

 and in the legs. They are universally present at the bases of the wings 

 (Fig. 44) and halteres (Fig. 45) and in the antennae (Graber, 1882 a, 

 1882 b; Schon, 1911; Vogel, 1912; Lehr, 1914; Eggers, 1928). They 

 occur segmentally in the abdomen. In many species simple chordo- 

 tonal organs are associated with the tracheal system (Demoll, 1917; 

 Larsen, 1955). They are especially numerous in larval insects, where 

 they stretch from one point on the body wall to another and criss- 



