LAND AND SEA. 311 



forms and structures of all organisms, to a great extent 

 correlated with, and perhaps dependent on, the former 

 set of changes. Combining these two great principles 

 with other ascertained causes of distribution, we shall 

 be enabled to deal adequately with the problem before 

 us, and give a rational, though often only an approxi- 

 mative and conjectural, solution of the many strange 

 anomalies we meet with in studying the distribution of 

 living things. 



Past and Present Distribution of Land and Sea. 

 Before proceeding to give details as to the distribution 

 of animals, it is necessary to point out certain geo- 

 graphical features which have had great influence hi 

 bringing about the existing state of things. 



The extreme inequality with which land and water is 

 distributed has often been remarked, but what is less 

 frequently noted is the singular way in which all the 

 great masses of land are linked together. Notwith- 

 standing the small proportion of land to water, the vast 

 difference in the quantity of land in the northern and 

 southern hemispheres, and the apparently hap-hazard 

 manner in which it is spread over the globe, we yet find 

 that no important area is completely isolated from the 

 rest. We may even travel from the extreme north of 

 Asia to the three great southern promontories Cape 

 Horn, the Cape of Good Hope, and Tasmania without 

 ever going out of sight of land ; and, if we examine a 

 terrestrial globe, we find that the continents in their 

 totality may be likened to a huge creeping plant, whose 

 roots are at or around the North Pole, whose matted 

 stems and branches cover a large part of the northern 

 hemisphere, while it sends out in three directions great 



