APPENDIX. 401 



so as to harmonize with our hypothesis of descent. The geo- 

 graphical barriers to diffusion (mountains, deserts, rivers, straits, 

 etc.), have not been taken into consideration in this general 

 sketch of migration, because, in earlier periods of the earth's 

 history, they were quite different in size and form from what 

 they are to-day. The gradual transmutation of catarrhine apes 

 into pithecoid men probably took place in the tertiary period in 

 the hypothetical Lemuria, and the boundaries and forms of the 

 present continents and oceans must then have been completely 

 different from what they are now. Moreover, the mighty in- 

 fluence of the ice period is of great importance in the question 

 of the migration and diffusion of the human species, although 

 it as yet cannot be more accurately defined in detail. I here, 

 therefore, as in my other hypotheses of development, expressly 

 guard myself against any dogmatic interpretation ; they are 

 nothing hut first attem])ts. 



VOL. II. 2 D 



