3l8 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. loo. 



42 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 Verwandtschaftsverhaltnisse, 

 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. 



43 Origin of Species. I3th ed. p. 84. 



44 Origin of Species. I3th ed. p. 96. 



45 Origin of Species. 



18 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. 



40 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 Munchner 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 (i.e. living together) is divergent. For extreme 

 characteristics are developed in them, whereas the eremitical 

 forms exhibit a medium in their characteristics. 



