242 DARWIN AND PALEONTOLOGY 



tions and retardations of characters in heredity 

 which remind us of the well understood laws of 

 acceleration and retardation in individual de- 

 velopment. 



Degrees of kinship also affect to a certain ex- 

 tent, but not absolutely, the time of appearance 

 or the time of origin of new characters as well as 

 the rate of their development. Thus four lines 

 of Eocene quadrupeds (Titanotheres) branched 

 off independently from one stock; in all the 

 branches we observe similar new cusps arising on 

 the premolar grinding teeth, and similar new 

 horn rudiments rising on the forehead above the 

 eyes, both independently evolved. Neither the 

 new cusps nor the new hornlets appear at just 

 the same moment of geological time ; some phyla 

 hasten forward these rectigradations, other phyla 

 retard them. 



The independence of single characters and 

 multiplicity of origins. The independence of 

 single characters reminds us of the independence 

 of the " unit characters " as known to the stu- 

 dents of MendeUsm and of De Vries' mutation, 

 yet the single characters we have in mind are not 

 unit characters in the Mendehan sense because 

 they do not mendehze ; they appear in every indi- 

 vidual. The independence of single characters 

 in the " Waagen mutations " or the " Osbom 

 rectigradations " is shown by the fact that a con- 

 siderable number of characters evolve in a per- 

 fectly regular and lawful succession. Each char- 



