518 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1917. 



that every one eucroaclies upon the territory of the others, not only by inter- 

 action but also by interpenetration. It has already been shown that the water 

 penetrates deep into the rock. Every spring that falls from the hillside gives 

 proof that the rocks above its level hold water, which they yield slowly as 

 a perennial supply ; and the innumerable hills of the continents and islands 

 have their innumerable springs. Every well proves that there is water below ; 

 every artesian fountain show^s the existence of underground waters ; and every 

 boring in the crust of the earth, and every excavation in underground mining, 

 discovers the presence of water. 



Wherever water flows, air flows with it, and all natural waters are per- 

 meated with air. 



The aqueous envelope is everywhere permeated with rock, which it holds in 

 solution or suspension, and there is no natural water absolutely pure. The sea 

 is full of salt. Salt lakes are more than full of salt, and so they must throw 

 it upon the bottom ; and the waters hold lime and many other substances. Not 

 a drop of pure water can be found in the sea ; not a drop can be found in a 

 lake; not a drop of pure water can be found in any river, creek, brook, or 

 spring ; and not a drop of pure water can be found underground ; it is all 

 mixed to some degree with rock. 



All natural waters are aerated. No drop of water unmixed with rock and 

 air can be found, except by the process of artificial purification. 



But surely there is pure air? Nay, not so. There is no natural air unmixed 

 with rock and water. All the air that circulates above the land and sea, within 

 the ken of man, and all the air which circulates undergi'ound, is- mixed with 

 rock and water. 



Pure air is invisible ; it will not reflect light ; it is transparent, but will not 

 convey light. Light is conveyed through the atmosphere by ether, and is 

 i-eflected and refracted by rock and water ; and it seems to be largely affected 

 in this manner by rock. If the ambient air of the earth were pure, there would 

 be no color in the sky, no rainbow in the heavens, no gray, no purple, no 

 crimson, no gold, in the clouds. All these are due largely to the dust in the 

 air. The purple cloud is painted with dust, and the sapphire sky is adamant 

 on wings. 



Land plants live on underground waters; were there no subterranean cir- 

 culation of water, there would be no land plants. Fishes live on underwater 

 air ; were there no circulation of subaqueous air, there would be no fishes in 

 the sea. The clouds are formed by particles of dust in the air, which gather 

 the vapor ; were there no dust in the air, there would be no clouds ; were there 

 no clouds, there would be no rain. 



Up to this point we have considered mainly the processes of main- 

 tenance of the animal body, but there are other processes as well 

 which must be called to mind, such as growth, development, multipli- 

 cation, and behavior. Physiologically considered, none of these 

 activities are essentially different from the fundamental phases of 

 metabolism and all are dependent upon it; they are special forms 

 of the transformation of substances and energy within the animal. 

 As the individual animal grows and develops in its life cycle, its 

 metabolism, form, and behavior change in an orderly manner, and 

 this transformation is in the main a continuous process like the other 

 transformations of matter and energy. The changes which take 

 place during ontogeny are often greater than the differences which 



