CHAPTER VII 



THE SENSE ORGANS 



In the Dragonfly the sense of sight is extraordinarily well- 

 developed, and is probably keener than in any other insect. This 

 sense alone suffices for the chase and capture of prey. It is, however, 

 supplemented by a fairly well-developed sense of taste, located in 

 the labrum and epipharynx. The sense of touch is well-developed 

 in most parts of the body, but particularly in the mouth-parts, 

 legs and abdominal appendages. 



Correlated with the great power of sight is the almost total 

 absence of the sense of smell. The antennae, which were originally 

 the seat of this sense (if indeed it was ever well-developed in these 

 insects), are much reduced, and incapable of anything beyond 

 feeble sensation. The sense of hearing, as we understand it, is 

 also practically absent; though there are certain minute organs 

 in the legs which are capable of receiving vibrations, and may be 

 looked upon as feeble auditory organs. 



The eyes are of two kinds, simple eyes or ocelli, and compound 

 or facetted eyes, made up of numerous separate elements. The 

 ocelli are used for near vision, their range probably lying between 

 a few millimetres and about an inch. The compound eyes, on 

 the other hand, observe objects from an inch or so up to several 

 feet off ; while their perception of movement, as distinct from form, 

 ranges very much further, probably up to fifty feet or more in 

 some cases. 



The Ocelli (fig. 61). 



These beautiful organs have so far received little attention 

 from biologists, though much has been written upon the compound 

 eyes. They are, nevertheless, of very great interest, and deserve 

 a more detailed study. They are three in number, and are so 



