APPENDIX. 



" In scientific investigations it is permitted to in- 

 vent any hypothesis, and if it explains various. large 

 and independent classes of facts, it rises to the rank 

 of a well-grounded theory." — Charles Darwin : Ani- 

 mals and Plants under Dojnestication^ vol. i., page 9. 



"The globe, when its continental area had become 

 in the main terra firma, may hence have had other 

 great areas unsolidified." — Dana's Manual of Geology. 



''That tendency which we see in the human races, 

 to overrun and occupy each other's lands as well as 

 the lands inhabited by inferior creatures, is a tendency 

 exhibited by all classes of organisms, in all varieties 

 of ways." — Herbert Spencer : Principles of Biology^ 

 vol. vii., page 315. 



" Any alteration in the temperature of a climate or 

 its degree of humidity, is unlikely to affect simulta- 

 neously the whole area occupied by a species ; and 

 further, it can scarcely fail to happen that the addition 

 or subtraction of heat or moisture will give to a part 



