1895,] Search for the Unknown Factors of Evolution. 437 
conditions have as yet been fulfilled, for hitherto organisms 
have been simply retained in a new environment, and the pro- 
found modifications which are exhibited may simply be the 
exponents of an hereditary mechanism acting under the influ- 
ence of new forces. Such experiments will probably require 
an extended period of time, for we learn from paleontology, 
as well as from palingenic variation, that phylogenic inheri- 
tance is extremely slow in a state of nature. 
It is desirable to establish non-infectious experimentation 
involving the conditions named above, mainly as a test of 
Lamarck’s factor. Varigny has also proposed a crucial experi- 
mental series mainly upon Buffon’s factor. His volume upon 
Experimental Evolution is an invaluable review, especially of 
French researches in experimental transformism. Much of 
this is in the line brought together some years ago by Semper 
in his Animal Life. Varigny draws a valid distinction between 
morphological variation and physiological variation, includ- 
ing under the latter internal chemical-and constitutional differ- 
ences which are not displayed in structure but must underlie 
all reactions. Under the head of what I have called Gona- 
genic Variation, the author discusses the work of Gautier” 
upon the influence of previous fertilization in plants as well 
as upon the chemistry of plants in connection with color varia- 
tion. He adds to the observations of Yung and Born other 
studies upon sex determination. He describes the experimen- 
tal teratogeny or embryonic variation of Dareste, Fallon, and 
later observers. 
Throughout Varigny’s volume it is nevertheless evident 
that none of the studies upon Ontogenic Variation hitherto 
have been specifically directed to the vital problem, as they 
must be in the future. Varigny makes a useful suggestion as 
to the importance of imitating natural conditions in exper- 
imental work, but he fails to emphasize the importance of the 
tests set forth above in order to ascertain whether the acquired 
modifications have actually been impressed upon the hered- 
23 Armand Gautier: Du Mécanisme de la Variation des Etres vivants. (Hom- 
mage à Monsieur Chevreul à l’Occasion de son Centennaire). F. Alcan. Paris, 
1886. 
