Masterpieces of Science 



tween the recent groups, is intelligible on the 

 theory of natural selection with its contingencies 

 of extinction and divergence of character. On 

 these same principles we see how it is that the 

 mutual affinities of the forms within each class 

 are so complex and circuitous. We see why 

 certain characters are far more serviceable than 

 others for classification; why adaptive characters 

 derived from rudimentary parts, though of no 

 service to the beings, are often of high classifi- 

 catory value; and why embryological characters 

 are often the most valuable of all. The real 

 affinities of all organic beings, in contradistinction 

 to their adaptive resemblances, are due to inherit- 

 ance or community of descent. The Natural 

 System is a genealogical arrangement, with the 

 acquired grades of difference, marked by the 

 terms, varieties, species, genera, families, etc.; 

 and we have to discover the lines of descent by 

 the most permanent characters, whatever they 

 may be, and of however slight vital importance. 

 The similar framework of bones in the hand of 

 a man, wing of a bat, fin of the porpoise, and leg 

 of the horse — the same number of vertebras form- 

 ing the neck of the giraffe and of the elephant — 

 and innumerable other such facts, at once ex- 

 plain themselves on the theory of descent with 

 slow and slight successive modifications. The 

 similarity of pattern in the wing and in the leg 

 of a bat, though used for such different purpose 

 — in the jaws and legs of a crab — in the petals, 

 stamens, and pistils of a flower, is likewise, to a 

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