138 THE ORIGIN AND EVOLUTION OF LIFE 



The Mutations of Waagen 



When Darwin published the "Origin of Species," in 1859, 

 no one had actually observed how one form of animal or plant 

 actually passes into another, whether according to some definite 

 law or principle, or whether fortuitously or by chance. So 

 far as we know, the honor of first observing how new specific 

 forms arise belongs to Wilhelm Heinrich Waagen.^ It was 

 among the fossil ammonites of the Jurassic, which are repre- 

 sented by the existing pearly nautilus, that Waagen first ob- 

 served the actual mode of transformation of one animal form 

 into another, as set forth in his classic paper of 1869, "Die 

 Formenreihe des Ammonites subradiatus.'''''^ The essential fea- 

 ture of the "mutation of Waagen"^ is that it established the 

 law of minute and inconspicuous changes of form which ac- 

 cumulate so gradually that they are observable only after a 

 considerable passage of time, and which take a definite direc- 

 tion as expressed in the word Mutationsrichtung. We now 

 recognize that they represent a true evolution of the heredity- 

 chromatin. This law of definitely directed evolution is illus- 

 trated in the detailed structure of the type series of ammon- 

 ites (Fig. 35) in which Waagen's discovery was made. It has 

 proved to be a fundamental law of the evolution of form, for 

 it is observed alike in invertebrates and vertebrates wherever 

 a closely successive series can be obtained. 



Among the fossil invertebrates a mutation series of the 

 brachiopod, Spirifer mucronatus of the Middle Devonian or 

 Hamilton time, is one of the most tyi^ical (Fig. 36). 



The essential law discovered by Waagen is one of the most 



1 Born in 1841, died in 1900. An Austrian palaeontologist and stratigraphic geologist. 



-Waagen, Wilhelm, 1869. 



* The term " mutation " used in this sense was introduced by Waagen in 1869. Twenty 

 years later the great Austrian palaeontologist Neumayr defined the " Mutationsrichtung " 

 as the tendency of form to evolve in certain definite directions. See Neumayr, M., 1889, 

 pp. 60; 61. 



