CHAP. 1. | INTRODUCTION. 9 
fessor Ernst Haeckel, Dr. Fritz Miiller,’ and others of 
their enthusiastic disciples and commentators. I do 
not think that I am speaking too strongly when I say 
that there is now scarcely a single competent general 
naturalist who is not prepared to accept some form 
of the doctrine of evolution. 
There is, no doubt, very great difficulty in the 
minds of many of us in conceiving that, commencing 
from the simplest living being, the present state 
of things in the organic world has been produced 
solely by the combined action of ‘atavism,’ the ten- 
dency of offspring to resemble their parents closely ; 
and ‘variation,’ the tendency of offspring to differ 
individually from their parents within very narrow 
limits: and many are inclined to believe that some 
other law than the ‘survival of the fittest’ must 
regulate the existing marvellous system of extreme 
and yet harmonious modification. Still it must be 
admitted that variation is a vera causa, capable, 
within a limited period, under favourable circum- 
stances, of converting one species into what, accord- 
ing to our present ideas, we should be forced -to 
recognize as a different species. And such being the 
_ case, it is, perhaps, conceivable that during the lapse 
of a period of time—stiil infinitely shorter than 
eternity—variation may have produced the entire 
result. 
1 Generelle Morphologie der Organismen. Allgemeine Grundziige 
der organischen Formen-Wissenschaft mechanisch begriindet durch 
die von Charles Darwin reformirte Descendenz-Theorie. Von Ernst 
Haeckel. Berlin, 1866.—Natiirliche Schépfungsgeschichte. Von Dr. 
Ernst Haeckel, Professor an der Universitit Jena. Berlin, 1870. 
2 Fir Darwin. Von Dr. Fritz Miiller. Leipzig, 1864. Translated 
from the German by W. S. Dallas, F.L.S. London, 1869. 
