10 THE STORY OF LIFE IN THE SEAS. 



lands and forests teeming with life, and the 

 great deserts and mountain tops inhabited only 

 by a few solitary Lizards, Birds or Insects. 



In order that we may fully understand, then, 

 the nature of the problems concerning the dis- 

 tribution of animals through the seas, it is of 

 importance to consider first the conditions under 

 which they must live in the different parts of 

 the ocean. A knowledge of geography is clearly 

 necessary for those who study the distribution of 

 terrestrial and aerial animals, and equally neces- 

 sary is it for those who wish to learn something 

 about the distribution of the aquatic animals, to 

 consider first of all the rudimentary principles of 

 hydrography. The principal Sea areas of our 

 globe may be roughly divided into two groups : 

 namely, the great oceans the Atlantic, Pacific 

 and Indian Oceans and the Inland seas, which 

 are partly enclosed by land, such as the German 

 Ocean, the Mediterranean Sea, and the Red Sea. 

 Taking the areas of the great oceans and the seas 

 together, we find that no less than 141 millions 

 of square miles, or nearly three-quarters of the 

 surface of the globe, are covered with water. 

 Moreover, these great areas are continuous, so 

 that it would be possible for an animal, other 

 conditions being favourable, to pass from any 

 one sea, such as the Black Sea, to any other, 

 such as the Hudson's Bay, without leaving the 

 water, an important fact in the consideration of 

 the distribution of marine forms of life. 



The depth of the sea varies very considerably 

 in the different parts of the world. In the inland 

 seas the water is comparatively shallow, but in 



