No. 580] ORIGIN OF SINGLE CHARACTERS 225 



habit and environment. This phyletic movement was 

 termed Mutations richtang by Neumayr. 



The significance of the term mutation as denned by 

 Waagen is to be found only in his original definition; 

 it has been used in many different senses before and 

 since. 15 It is a taoconomic term for each of the minute 

 subdivisions of a specific phylum which may be defined 

 by certain degrees of advance in " mutation-characters' ' 

 evolving continuously in definite directions. The verte- 

 brate paleontologist Deperet in 1907 pointed out that the 

 Waagen "mutation-characters" have this special charac- 

 teristic, they are always produced in the same direction 

 without oscillations or retarded steps. The lacunae are 

 so infrequent as not to interrupt the general view of the 

 continuity. Each of the closely linked terms of any 

 series may be designated as "ascending mutations" in 

 rising strata. It becomes possible to recognize the in- 

 tensity of the action of time. 



The mutations of Waagen demonstrate five very im- 

 portant principles in the evolution of certain "least char- 

 acters" as follows: (1) origin from inconspicuous begin- 

 nings; (2) continuity rather than discontinuity; (3) defi- 

 nite direction or Mutat i<>i/sr/< Ithuifj rather than indefinite 

 or variable evolution; -(4) a definite rate of phyletic 

 movement. 



These principles appear to involve a hereditary or 

 germinal basis, a Mutationsrichhnig, such as also appears 

 to underlie Osborn's rectigradations. 



The two kinds of characters observed by Waagen 16 are 

 also exactly similar to those observed by field zoologists 

 and by vertebrate paleontologists, namely : 



