156 THE SENSE ORGANS [CH. VII 



warn the Dragonfly of the approach either of an enemy or a victim. 

 They would be particularly useful at night-time, when the eyes 

 are probably of little use. 



Stridulating Organs. 



Berlese [10, p. 174] has figured two small processes (laminae 

 stridulatoriae) situated one on either side of theprothorax anteriorly, 

 above the prosternum, in Aeschna. These he described as stridu- 

 lating organs, which produce a sound by rubbing against two 

 roughened patches behind the eyes, on either side of the posterior 

 foramen. I know of no other observations on stridulation in 

 Dragonflies, nor have I ever heard them emit any sound, except 

 a sharp click of the wings occasionally when flying. In view, 

 however, of the proved presence of minute auditory organs on the 

 antennae, it is clear that more observations are required on this 

 interesting point. 



Other Sense Organs. 



Minute organs of taste and touch occur scattered all over the 

 mouth parts. They are however nowhere numerous, except on 

 the labrum and epipharynx. Sensory hairs, with a tactile function, 

 occur on many parts of the body, such as the antennae, the edge 

 of the labrum, the legs, the abdomen, the anal appendages, and 

 on the wing-sheaths of many larvae. 



To sum up, the Dragonfly shares with the Bird the distinction 

 of possessing the keenest vision of any animal in its Phylum. 

 In both cases, the exceptional development of the sense of sight 

 is correlated with an aerial existence. The senses of taste and 

 touch are normally developed. But the senses of smell and hearing 

 are very poor, the former being almost, if not quite, absent, while 

 the latter is confined to organs of excessively minute size. To 

 these five senses, as ordinarily understood, we must add the sense 

 of direction or orientation, which is probably located in the tym- 

 panulae. The larvae may, perhaps, also possess a kind of chemical 

 sense for gauging the purity of the water. 



