Sensory Organs of Insects 85 



repeated over and over again without the wasp 

 taking any notice of the surrounding dead 

 insects. 



The olfactory sensory organs of insects con- 

 sist of structures adapted to receive and trans- 

 mute a special form of energy into one which, 

 on reaching certain cerebral centres, becomes 

 manifest in the sensation we designate odour. 

 By the sense of smell, therefore, we mean the 

 response made by a specialised system of living 

 matter to definite modes of energy derived from 

 certain bodies. 1 The olfactory sensory organs 

 of insects are located on their antennae among 

 the tactile setae; they are supplied by terminal 

 branches of the antennary nerves which arise 

 from nerve cells located in the animal's mid- 

 brain. 



The different genera of ants, which under 

 ordinary conditions are natural enemies and 

 fight to the death when they meet, after 

 having had their antennae excised may be kept 

 together in the same box, where they live on 



1 There are hardly any metallic or other bodies which do not 

 manifest, especially on friction, odour of their own. Berthelot 

 calculates that one gram of iodoform only loses the hundredth 

 of a milligram in a hundred years, thcugh continuously emitting 

 a flood of odoriferous particles in all directions. 



