74 THE GENESIS OF SPECIES [Cqap. 



modified limbs at all ; or we may even find the function 

 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 fur- 

 nished with special structures of very different kinds. The 

 various modes by which such seeds are dispersed are well 

 expressed by ^Nlr. Darwin. He says : ^ " Seeds are dissemi- 

 nated by their minuteness, — by their capsule being con- 

 verted into a light balloon-like envelope, — l)y being 

 embedded in pulp or flesh, formed of the most diverse 

 l)arts, 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." 



Again, if we consider the poisoning apparatus possessed 

 l)y different animals, we find in serpents a perforated — or 

 rather very deei)ly channelled — tooth. In wasps and bees 

 the sting is formed of modified parts, accessory in repro- 

 duction. In the scorpion, we have the median terminal 

 process of the body specially organized. In the spider, we 

 liave a specially constructed antenna ; and finally, in the 

 centipede a pair of modified tlioracic liml)s. 



It would be easy to produce a nmltitude of such instances 

 of similar ends being attained by dissimilar means, and it 

 is here contended that by "the action of Natural Selection" 

 only it is so im])robable as to be practically impossible for 

 two exactly similar structures to have ever been indepen- 



1 "Origin of Sj>ccies," 5th cuition, p. 235. 



