Progression, Rctrogrcssioji and Degression. 71 



existence of latent characters. I shall refer to this mode 

 of formation of species as degressive. In it, that which 

 arises is always something new, and often something 

 strikingly new, hut usually without any clear relation to 

 the progressive development on the main lines of evolu- 

 tion. They form, rather, lateral improvements of types 

 already existing. 



Degressive formation of species is therefore due to 

 the activation of long estahlished latent characters. Of 

 these, as Goebel has shown in his Organographies there 

 are two types to he distinguished.^ Either the character 

 in question was active in the earlier ancestors, or it was 

 not. In the former case we have an instance of reversion 

 or atavism, and moreover a genuine systematic reversion, 

 at least inasmuch as the ancestral relation can be demon- 

 strated. In the other case we have only the development 

 of a specific character from a taxinomous anomaly. 



It is perhaps hardly necessary to state that the appli- 

 cation of this criterion of grouping can only be effected 

 at the present moment in a relatively small number of 

 cases. The information at our disposal does not as yet 

 meet the demands of such a system. On the physiolog- 

 ical side, however, the question of prime importance is 

 only the distinction between the chief groups; so that we 

 will only lay stress on that point here . 



Bearing this limitation in mind we can summarize 

 what we have already said, as follows: 



THE ORIGIN OF NEW SPECIES. 



A. By the formation of new characters : Progressive 

 specific differentiation. 



B. A\^ithout the formation of new characters. 

 ' K. Goebel, Organographic, Vol. I, p. 170. 



