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THE AMERICAN NATURALIST [Vol. XL. VI 



that such individual differences were in the nature of 

 minor saltations of character, structural or functional, 

 and always hereditary. Since Darwin observes that 

 natural selection may be strictly compared with the slow 

 and gradual improvement of the racehorse, grayhound, 

 etc., if we collect all the observations which he assembled 

 as to the genesis of the racehorse and grayhound we may 

 gain a concrete understanding of his opinions as to the 

 genesis of species. It will appear that many of the new 

 characters which Darwin cites, and he used the term 

 ''new characters" interchangeably with "individual dif- 

 ferences," are clearly identical with minor saltations or 

 with the "mutations of De Vries," as generally under- 

 stood by zoologists to-day. 



"We may therefore conclude," observes Darwin, 4 

 "that, whether or not the various existing breeds of the 

 horse have proceeded from one or more aboriginal stocks, 

 yet that a great amount of change has resulted from the 

 direct action of the conditions of life, and probably a still 

 greater amount from the long-continued selection by man 

 of slight individual differences." Among the examples 

 he cites in amplification of this conclusion are the fol- 

 lowing : 



(1) Eight incisors or two super-normal; (2) canines in 

 females; (3) a nineteenth or posterior rib; (4) a supple- 

 mentary hock-bone; (5) a reversional trapezium and 

 Mtc.V; (6) horn rudiments in the frontal bones one or 

 two inches in length; (7) tailless foals which, he observes, 

 might have produced a new breed; (8) curled hair corre- 

 lated with short manes and tails and mule-like hoofs. 



All the above "individual differences" are cited by 

 Darwin as hereditary; all are "discontinuous" in Bate- 

 son's sense or "mutations" in De Vries 's sense. In other 

 parts of Darwin's works most of the numerous references 

 made to "individual variations" in horses are of the 

 same character, namely, saltatory and hereditary. Al- 

 though (5) cited above is a "reversion," reversions and 



♦"Animals and Plants under Domestication," Vol. I, p. 55. 



