1304 THE STORY OF THE UNIVERSE 



sense ; in some of them it is even difficult to discover 

 a vestige of circulation; their respiratory organs are 

 almost universally seated on the surface of the body, 

 the intestine in the greater number is a mere sac 

 without issue, and the lowest of the series are nothing 

 but a sort of homogeneous pulp, endowed with 

 motion and sensibility. 



DEEP SEA FAUNA 



LORD KELVIN 



NEARLY all the animals at extreme depths 

 practically all the animals, for the small num- 

 ber of higher forms feed upon these belong to one 

 sub-kingdom, the Protozoa; whose distinctive char- 

 acter is that they have no special organs of nutrition, 

 but absorb nourishment through the whole surface of 

 their jelly-like bodies. Most of these animals secrete 

 exquisitely formed skeletons, some of silica, some of 

 carbonate of lime. There is no doubt that they ex- 

 tract both these substances from the sea-water; and 

 it seems more than probable that the organic matter 

 which forms their soft parts is derived from the same 

 source. It is thus quite intelligible that a world of 

 animals may live in these dark abysses, but it is a 

 necessary condition that they must chiefly belong to 

 a class capable of being supported by absorption 

 through the surface of their bodies of matter in solu- 

 tion, developing but little heat, and incurring a very 

 small amount of waste by any manifestation of vital 

 activity. According to this view it seems probable 

 that at all periods of the earth's history, some form 



