318 THE DOCTRINE OF DESCENT. 
These, and similar thoughts in the work of Malthus, first sug- 
gested Darwin’s theory, as he has informed us. 
41 Variation of Animals and Plants. I. 100, 
# Two treatises by A. Kerner are also very instructive with 
regard to the question of species: “ Gute and Schlechte Arten.” 
(Innsbruck, 1866.) And “ Die Abhangigkeit der Pflanzenwelt von 
Klima und Boden. Ein Beitrag zur Lehre von der Enstehung und 
Verbreitung der Arten, gestiitzt auf die Verwandtschaftsverhiltnisse, 
geographische Verbreitung und Geschichte der Cytisusarten aus 
dem Stamme Tubocytisus D.C.” 1869. Kerner’s latest work, “ Die 
Schutzmittel des Pollens” (Innsbruck, 1873) is likewise an admirable 
investigation of the variability, adaptation, and formation of species. 
* Origin of Species. 13th ed. p. 84. 
* Origin of Species. 13th ed. p. 96. 
“© Origin of Species. 
#®P,7. The following pages contain an epitome of the objec- 
tions offered to the inadequacy of the theory of selection. 
47 Moritz Wagner, Die Darwin’sche Theorie und das Migrations- 
gesetz der Organismen, 1848. 
4® Nageli, Enstehung und Begriff der naturhistorischen Art. 
(Sitzungsberichte der bairischen Akademie der Wissenschaften), 
1865. Nageli’s later investigations (Sitzungsberichte der mathe- 
matisch-physikalischen Klasse der Miinchner Akademie, 1872, 
p. 305) confirm the doctrine of descent. He shows that the grega- 
riousness of merely allied species and their varieties proves more 
favourable to the formation of species than isolation, “ The asso- 
ciated forms—of certain Alpine plants—have, as it were, recipro- 
cally modified one another ; they exhibit, to express myself thus, 
a specific social type, which is different in each assemblage, and 
therefore in every neighbourhood. This fact incontrovertibly 
shows that the forms have altered since they were associated. 
“The specific social type consists in their showing a notable 
accordance in certain characteristics, while in others they repre- 
sent extremes, and in these sometimes exceed all their congeners 
in other districts. 
“From these facts it follows undoubtedly that the movement in 
the cenobitic forms (z.e. living together) is divergent. For extreme 
characteristics are developed in them, whereas the eremitical 
forms exhibit a medium in their characteristics. 
