Progression, Retrogression 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, but 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 established latent characters. Of 
these, as GOEBEL has shown in his Organographie, there 
are two types to be distinguished. 1 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. Without the formation of new characters. 
1 K. GOEBEL, Organographie, Vol. I, p. 170. 
