DARWIN AND PALEONTOLOGY 



tions." ^ It appears probable, but it is not yet 

 demonstrated, that the rectigradations of Osborn 

 are of the same nature as the mutations of 

 Waagen. Scott ^ in 1894 was the first vertebrate 

 paleontologist to call the attention of his co- 

 workers to Waagen's law among the inverte- 

 brates. This principle of rectigradation in the 

 origin of many new characters in the mammals 

 cuts both ways; it demonstrates the absence of 

 the chance happenings without direction, which 

 form the basis of Darwin's hypothesis of the 

 origin of adaptations, and positively shows that 

 certain new adaptive characters appear definitely 

 and assume adaptive direction from their very 

 minutest beginnings. 



To sum up, the law of gradual change in cer- 

 tain determinate, definite, and at least in some 

 cases adaptive directions, through very long 

 periods of time, and the absence of chance or non- 

 direction in the origin of a large number of 

 adaptive and other new characters, is the com- 

 mon working principle both in vertebrate and 

 invertebrate paleontology. 



It is thus that the characters which the older 

 paleontological observers, such as Owen, Leidy, 

 Cope, and Marsh, designated as specific and even 

 as generic are gradually built up. We thus wit- 



' " Homoplasy as a Law of Latent or Potential Homology," 

 American Naturalist, Vol. XXXVI, April, 1902, pp. 259- 

 71. 



'Scott, W. B.: "On Variations and Mutations," American 

 Journal of Science, Vol. XL VIII, 1894, pp. 355-74. 



