The Odonaia or Dragon-flies of South Africa. 



249 



pound eye. Vision is evidently the dominant sense of the dragonfly ; 

 parallel with the hypertrophy of the eye we find an extreme reduction 

 of the antennae — the organs of scent. A similar combination is 

 found in the Order Ephemeridae or Mayflies, and to some degree in 

 many of the more highly specialised Diptera. The configuration of 

 the compound eyes largely affects in dragonflies the arrangement of 

 the other parts of the head, and a better idea than any description can 



Fio. 2. — Podogoinph%is 



raetorius. Dorsal, frontal and ventral views of head. 

 Lettering as in Text-fig. 1. 



give will be conveyed by our Text-figs. 1-3, where three modifications 

 are shown : the zygopterous head with widely separate, almost 

 hemispherical eyes, in Text-fig. 1 ; the Gomphine head, which is 

 intermediate between the zygopterous and the regular anisopterous 

 configuration in Text-fig. 2 ; the Libelluliue head in Text-fig. 3 is a 

 representative of this fully developed anisopterous configuration, 

 where the eyes meet in the median line for some length. Three 

 ocelli are present in the entire order ; their position is open in the 



