and smooth or simple Eyes of Insects. 282 



all external objects in this direction, while the smooth eye in 

 the front and centre would inform them of the obstacles which 

 they might ex]3ect to find when advancing in a straight line. It 

 IS to be observed that, in this arrangement, tiie lateral smooth 

 eyes are very little controled by the compound eyes, and that 

 the eye in -the centre is ahva}s calcuiated more directly for any 

 obstacle wliicli shculd oppose the advance of the insect. Some- 

 times, however, tlie smooth eyes are arrai:ged in the form of a 

 triangle on the crown of the head ; wlien they can only be use- 

 ful in enabling the insect to perceive objects placed above it. 

 Indeed, those wliich exhibit this disposition Io-,ver the head so 

 as to enable them to see straight forward. Bees and certain 

 species of wasps, as well as the maniei, v.hich have their smooth 

 eyes on the summit of their head, know very well liow to incline 

 it, the better to distinguish objects })laced before them. 



The facts which we have detailed, seem positive enough to 

 permit us to conclude, 



1. That we must never judge of the extent or perfection of 

 any sense, from the simplicity of the organ destined to produce 

 It ; for, if we regard only the little degree of complication in 

 the eyes of insects, we might presume either that these animals 

 do not see at ail, or at least that they have not a very distinct 

 vision. Facts, however, prove not only that they are not myopes^ 

 but also that they perceive objects at great distances. 



2. That the eyes of insects have no relation with those of 

 any other class, and that this organ, like all those of this order 

 of animals, cannot be assimilated, nor even compared, to any 

 other which performs the same functions in a different order of 

 animals. Thus, we always run the risk of establishing inaccurate 

 relations, when we endeavour to compare the organs of insects 

 with those of the other invertebral animals, and afmlmi with 

 those of the vertebral. In fact, insects are so formed, on a par- 

 ticular plan, that we ought never to establish any parallel with 

 respect to their organs, except between the species of different 

 orders. We may therefore say that, correctly speaking, these 

 animals ought to be compared with each other only, because, 

 in the immense chain of organized beings, they alone present 

 the remarkable peculiarity of having no other fluid in circula- 

 tion but air. Tliis disposition of not presenting any ramified 

 vessels- but those destined to give play, through all the parts of 

 the body, to the impression of this subtle fluid, the aliment of 

 life as it is of flame, ought necessarily to have brought with it 

 a crowd of differences in organization, which we would seek for 

 elsewhere in vain. The nervous system is the only one which 

 still shows that all the articulated animals have been formed oo 



