370 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



the animals. In consequence land animals have become subdivided 

 into an indefinite number of different forms or minor types each 

 most efficient within a small range of conditions. 



But all land animals have one thing in common; they must seek 

 their food; it will not come to them. Therefore land animals are 

 almost wholly of those types, arthropods and vertebrates, best fitted 

 for locomotion, with representatives of some other types of fair loco- 

 motor powers. 



In the sea conditions are quite different. The temperature range 

 is small. At no place temperatures of less than 28.4° are found, 

 while high temperatures, even in the Tropics, are confined to a thin 

 superficial layer. The great bulk of sea water ranges in temperature 

 between 35° and 60°. The chemical conditions are only slightly 

 variable. The salinity varies somewhat, but the different salts are 

 everywhere present in about the same proportion. Motion affects 

 only the surface waters, and is negligible except along the shores. 



In the sea, food substances float everywhere suspended in the 

 water, drifting back and forth and up and down ; abundant food lies 

 also on the bottom. While useful, powers of locomotion are not 

 necessary for the creatures in the sea; if they can not seek their 

 food it will be brought to them. 



Thus in the sea the food relations of the animals are of three 

 kinds; some go after it, as do the animals on land; some attach them- 

 selves or burrow in the bottom and let the water do the work of 

 bringing food to them; and some float suspended in their food 

 supply. 



Three possible ways of obtaining food instead of one mean a cor- 

 responding diversity in the fundamental structure of the animals 

 involved; but the relative uniformity of the physical and chemical 

 conditions in the sea permit the existence of these major types with 

 relatively slight subdivision. 



THE BASIS OP LIFE IN THE SEA 



What is the biological significance of a large whale? The im- 

 mediate answer is that the largest whale, the blue or sulphur-bottom, 

 is the largest animal known, living or extinct, reaching a length of 

 90 feet. The weight of such a monster has not been determined; 

 but a torpedo boat of the same length with approximately the same 

 underwater contour would displace 32 tons. If we assume a weight 

 of 30 tons for the largest whale we shall not be far out of the way. 



All whales are carnivorous; but all the fishes, cuttle-fish and 

 smaller creatures upon which they feed, are dependent ultimately 

 upon plant life for their existence. How much vegetable material 

 does it take to support a whale? 



