92 ZOOLOGICAL PHILOSOPHY 



larvae of the insects of the two last orders have no legs and are like 

 worms. 



It appears that the insects are the last animals which have a quite 

 distinct sexual reproduction and are probably oviparous. 



Lastly, we shall see that insects are rendered highly remarkable 

 by what is called their skill ; but this alleged skill is far from being 

 the product of any thought or any combination of ideas on their 

 part. 



Observation. 



Just as among the vertebrates the fishes display in their general 

 conformation and anomalies of organisation the product of the action 

 of their environment ; so the insects among the invertebrates exhibit, 

 in their shape, organisation and metamorphoses, the obvious effects 

 of the action of the air in which they live ; for most of them launch 

 themselves into it and habitually maintain themselves there like 

 birds. 



If the insects had had lungs, if they had been able to swell them- 

 selves out with air, and if the air which penetrates into every part 

 of their body could have there become rarefied like that which is intro- 

 duced into the body of birds, their hair would no doubt have changed 

 into feathers. 



Lastly, if among invertebrate animals we are surprised to find so 

 few affinities between the insects which undergo remarkable meta- 

 morphoses and other classes of invertebrates, let us remember that 

 these are the only invertebrate animals which launch themselves into 

 the air and there execute movements of progression ; we shall then 

 no longer be surprised that such pecuUar conditions and habits must 

 have produced peculiar results. 



The insects are allied only to the arachnids by their affinities, and in 

 fact these two are in general the only invertebrate animals that live in 

 the air ; but no arachnid has the faculty of flight ; none therefore 

 undergoes metamorphosis ; and when I come to treat of the influence 

 of habits, I shall show that these animals, being accustomed to remain 

 on the surface of the earth and to hve in retreats, must have lost a 

 part of the faculties of insects- and acquired characters which con- 

 spicuously distinguish the two groups. 



Extinction of Several Organs essential to the 

 Most Perfect Animals. 



After the insects it appears that there is a rather large gap in the 

 series remaining to be filled by animals not yet observed ; for in this 

 part of the series several organs essential to the most perfect animals 



