When we go to lower animals, we find flight produced by organs, as the wings of insects, which are not even modified limbs at all; or we find even the function sometimes subserved by quite artificial means, as in the aerial spiders, which use their own threads to float with in the air.

In the vegetable kingdom the atmosphere is often made use of for the scattering of seeds, by their being furnished with special structures of very different kinds.

The diverse modes by which such seeds are dispersed are well expressed by Mr.Darwin.He says:[50] "Seeds are disseminated {66} by their minuteness,--by their capsule being converted into a light balloon-like envelope,--by being embedded in pulp or flesh, formed of the most diverse parts, and rendered nutritious, as well as conspicuously coloured, so as to attract and be devoured by birds,--by having hooks and grapnels of many kinds and serrated awns, so as to adhere to the fur of quadrupeds,--and by being furnished with wings and plumes, as different in shape as elegant in structure, so as to be wafted by every breeze." [Illustration: SKELETON OF THE FLYING-DRAGON.
(Showing the elongated ribs which support the flitting organ.)] Again, if we consider the poisoning apparatus possessed by different animals, we find in serpents a perforated--or rather very deeply channelled--tooth.

In wasps and bees the sting is formed of modified parts, accessory in reproduction.

In the scorpion, we have the median terminal process of the body specially organized.