£895.] Search for the Unknown Factors of Evolution. 433 
Galton has discussed the subject objectively under the head 
of ‘Stability of Sports,’ and Emery, under the head of ‘ Primary 
Variations,’ has supported Galton’s observation that such salta- 
tions often exhibit a strong capacity for inheritance. Bateson 
reaches in the conclusion of his work a modified form of St. 
Hilaire’s factor of saltatory evolution, and believes that species 
have largely originated by ‘ discontinuity ’ of variation or the 
sudden accession of new characters from unknown causes, con- 
cluding that all inquiry into the causes of variation is pre- 
mature. The materials he has brought together are of the 
greatest value, and he has already been able to throw in doubt 
many current beliefs, such as that variability is greater in 
domestic than in wild animals. His interpretation of these 
materials is,as we have seen, weakened, so far as it bears on 
our search for the evolution factors, by the fact that from the 
nature of most of his evidence he cannot discriminate between 
ontogenic aud phylogenic variation; moreover, he discards 
any attempt to discriminate between palingenic and cenogenic 
variations. This lack of analysis leads him into what appears 
to be an entirely erroneous induction, for the principle of dis- 
continuity is opposed by strong evidence for continuous and 
definite phylogenic variation as observed in actual phyletic 
series. 
Nacetrs FACTOR AND PHYLOGENIC VARIATION. 
Niigeli’s factor introduces us to an entirely distinct territory 
—to the opposite extreme from saltation. It is one we can no 
longer set aside as transcendental because of the strong like- 
ness it bears at first sight to the internal perfecting principle 
of Aristotle. It is supported in a guarded manner by Kölliker 
and Ziegler. It contains the large element of truth that the 
trend of variation and hence of evolution is predestined by the 
constitution of the organism ; that is, granted a certain hered- 
itary constitution and an envi tfavoring its develop t 
this development will exhibit certain definite directions, which 
18C; v. Nägeli: Mechanisch-physiologische Theorie der Abstammungslehre. 
München und Leipzig, 1884. i 
