2G»i THE ORIGIN OF SPECIES 



sitic mites (Acaridae), belonging to distinct sub-families 

 and families, which are furnished with hair-claspers. 

 These organs must have been independently developed, 

 as they could not have been inherited from a common 

 progenitor; and in the several groups they are formed by 

 the modification of the fore-lec:s — ^of the hind-legs — of the 

 maxillae or lips — and of appendages on the under side of 

 the hind part of the body. 



In the foregoing cases, we see the same end gained 

 and the same function performed, in beings not at all 

 or only remotely allied, by organs in appearance, though 

 not in development, closely similar. On the other hand, 

 it is a common rule throughout nature that the same end 

 should be gained, even sometimes in the case of closely- 

 related beings, by the most diversified means. How dif- 

 ferently constructed is the feathered wing of a bird and 

 the membrane- covered wing of a bat; and still more so 

 the four wings of a butterfly, the two wings of a fly, 

 and the two wings with the elj^tra of a beetle. Bivalve 

 shells are made to open and shut, but on what a number 

 of patterns is the hinge constructed — from the long row 

 of neatly interlocking teeth in a Nucula to the simple 

 ligament of a Mussel! Seeds are disseminated by their 

 minuteness — by their capsule being converted into a light 

 balloon -like envelope — by being imbedded in pulp or 

 flesh, formed of the most diverse parts, and rendered 

 nutritious, as well as conspicuously colored, so as to 

 attract and be devoured by birds — by having hooks and 

 grapnels of many kinds and serrated awns, so as to ad- 

 here to the fur of quadrupeds — and by being furnished 

 with wings and plumes, as different in shape as they are 



