Chap. VI. OF NATURAL SELECTION. 1S7 



adapted to live more and more out of "water, and to breathe 

 the air. For these species, from beloiif^ing to distinct families, 

 ■would difler to a certain extent, and in accordance with the 

 principle that the nature of each variation depends on two fac- 

 tors, viz., the nature of the orp^anism and that of the condi- 

 tions, the variability of these crustaceans assuredly would not 

 have been exactly the same. Consequently natural selection 

 would have had diiTerent materials or variations to work on, in 

 order tu arrive at the same functional result; and the structures 

 thus acquired would almost necessarily have dillered. On the 

 hypotliesis of 6C]>arate acts of creation the whole case remains 

 unintelli,Lrible. The above line of arn^mcnt, as advanced by 

 Fritz Miiller, seems to have had j^reat weiglit in leadino^ this 

 distin<^uislicd naturalist to accept the views maintained by me 

 in this volume. 



• In the several cases just discussed, wc have seen that in 

 beings more or less remotely allied, the same end is gained 

 and the same function performed by organs in appearance, 

 though not in truth, closely similar. But the common rule 

 throughout Nature is that the same end is gained, even some- 

 times in the case of beings closely related to each other, by the 

 most diversified means. How differently constructed is the 

 feathered wing of a bird and the membrane-covered yying of a 

 l)at with all the digits largely developed ; and still more so the 

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

 wings of a beetle, together with the elytra ! 13ivalve shells 

 are made to open and shut, but on what a immber of ])atterns 

 is the hinge constructed, from the long row of neatly inter- 

 locking teetli in a Nucula to the simple ligament of a Mussel ! 

 tSeeds arc disseminated by their minuteness — by their capsule 

 being converted into a light balloon-like envelope — by being- 

 embedded in pulp or flcsli, formed of tlie most diverse parts, 

 and rendered nutritious, as well as conspicuously colored, so as 

 to attract and be devoured by birds — ])y having hooks and 

 grapnels of many kinds and serrated awns, so as to adhere to 

 the fur of quadmpeds — and by being furnish(>d Avith wings and 

 plumes, as different in shape as elegant in structure, so as to 

 be wafted by every breez(\ I will give one other instance ; 

 for this subject of the same end being gained by the niost di- 

 versified means well deserves attention. Some authors main- 

 tain that organic beings have been formed in many ways for 

 the sake of mere variety, almost like toys in a shop, but such a 



