INSECTS IN GENERAL. 6l 



have produced not only the voluntary motion of the insects 

 towards the place where the odorant molecules were floating, 

 but that, moreover, deceived by this illusory sensation, the 

 insect has been induced to deposit its eggs on a substance 

 which its smell alone had indicated as proper for their recep- 

 tion ? 



" Do we not observe bees, wasps, sphinxes, butterflies, and 

 all insects which live on the juices of vegetables, or nectar of 

 flowers, arrive in great numbers towards the plant which 

 produces them, as soon as they begin to flow, or the petals 

 are opened ? 



" Perfectly vain is it to attempt to explain this attraction, 

 this movement, by the visual sensation of the insect; for, in 

 spite of all the care of florists in covering their tulips, in 

 spite of those of the grocer, whose honey is concealed in 

 proper vessels, the insect comes, attracted by the odour, and 

 tries all efforts to get at the place from which it directly 

 emanates. 



" The insects then, possess the sense of smelling. But in 

 what part of their body is the organ of this perception ? It 

 is probable that this sensation is produced in them as in all 

 other animals, through the respiratory organ. But, in in- 

 sects, respiration takes place through numerous orifices, 

 which correspond to the majority of the rings of the body, 

 except at the head. These apertures are named stigmata, 

 all of which lead to the tracheae, or vessels with elastic 

 parietes, always filled with the circumambient air, which 

 doubtless arrives there, charged with odorant particles, as 

 happens to other animals. But does the gas thus penetrate 

 into the net-work of the air-vessels, or does it deposit these 

 molecules at the very entrance of the stigmata ? This is not 

 easy to decide, as wo do not ourselves experience this sort of 

 sensation ; for certainly, we should have no idea of the admi- 

 rable function of the pituitary membrane of animals, if we 



