22 THE PHYSIOLOGY OF INSECT SENSES 



rods, and it now appears that such structures are a constant feature of 

 insect sensilla. In recognition of this fact Snodgrass (1926) originally 

 preferred the term chordotonal in deference to custom ; however, he 

 later (1935) switched to the term scolopophorous sensillum. Neither 



Fig. 15. Sensillum coeloconicum from the antenna of a grasshopper. N, 

 bipolar neuron; S, scolopoid sheath; A, axons; D, dendrites; Tr, 

 trichogen cell; To, tormogen cell; M, dried residue from moulting 

 fluid. (Redrawn from Slifer et al, 1959.) 



term seems singularly appropriate, so the choice at the moment is a 

 matter of taste (for a complete discussion of this matter see Eggers, 

 1923, 1924, 1928; Snodgrass, 1926, 1935). 



A typical sensillum consists of a minimum of four cells (Fig. 16): 

 (1) the trichogen or hair-forming cell; (2) the tormogen or socket- 



