404 LAMARCK, AIS LIFE AND WORK 
ment and the habits of the animal were the efficient 
cause of the change, and any explanation which ex- 
cludes the direct action of such agencies is con- 
fronted by the difficulty of an immense number of 
the most’ striking coincidences 2). So. fateas 
I can see, the theory of determinate variations and 
of use-inheritance is not antagonistic but supple- 
mentary to natural selection, the latter theory at- 
tempting no explanation of the causes of variation. 
Nor is it pretended for a moment that use and disuse 
are the sole or even the chief factors in variation.”’ 
As early as 1868 the Lamarckian factor of isola- 
tion, due to migration into new regions, was greatly 
extended, and shown by Moritz Wagner* to be a 
most important agent in the limitation and fixation 
of varieties and species. 
‘© Darwin’s work,’’ he says, ‘* neither satisfactorily 
explains the external cause which gives the first im- 
pulse to increased individual variability, and con- 
sequently to natural selection, nor that condition 
which, in connection with a certain advantage in the 
struggle for life, renders the new characteristics indis- 
pensable. The latter is, according to my conviction, 
solely fulfilled by the voluntary or passive migration 
of organisms and colonization, which depends in 
a great measure upon the configuration of the coun- 
try; so that only under favorable conditions would 
the home of a new species be founded.”’ 
* «« Uber die Darwinische Theorie in Besug auf die geographische 
Verbreitung der Organismen.” Sitzenb. der Akad. Miinchen, 1868. 
Translated by J. L. Laird under the title, Zhe Darwinian Theory 
and the Law of the Migration of Organisms, London, 1873. Also 
Ueber den Einfluss der geographischen Isolirung und Colonierbildung 
auf die morphologischen Ver dnderungen der Organismen. Miinchen, 
1870. 
