Y6 THE DATA OF BIOLOGY. 



stance in the environment capable of transformation into its 

 own tissue ; but that the introduction of these masses into its 

 stomach, shall be followed by the secretion of a solvent fluid 

 that will reduce them to a fit state for absorption. Special 

 outer properties must be met by special inner properties. 



When, from the process by which food is digested, we 

 turn to the processes by which it is seized, we perceive the 

 same general truth. The stinging and contractile power of 

 a polype's tentacle, correspond to the sensitiveness and 

 strength of the creatures serving it for prey. Unless that 

 external change which brings one of these creatures in con- 

 tact with the tentacle, were quickly followed by those inter- 

 nal changes which result in the coiling and drawing up of 

 the tentacle, the polype would die of inanition. The funda- 

 mental processes of integration and disintegration within it, 

 w^ould get out of correspondence wath the agencies and pro- 

 cesses without it ; and the life would cease. 



Similarly, it may be shown that when the creature be- 

 comes so large that its tissue cannot be efficiently supplied 

 with nutriment by mere absorption through its limiting 

 membranes, or duly oxygenated by contact with the fluid 

 that bathes its surface, there arises a necessity for a circu- 

 latory system by which nutriment and oxygen may be dis- 

 tributed throughout the mass ; and the functions of this sys- 

 tem, being subsidiary to the two primary functions, form 

 links in the correspondence between internal and external 

 actions. The like is obviously true of all those subordinate 

 functions, secretory and excretory, that facilitate oxidation 

 and assimilation — functions in which we may trace, both co- 

 temporaneous changes answering to co-existences in the en- 

 vironment, and successive changes answering to those changes 

 of composition, of temperature, of light, of moisture, of pres- 

 sure, which the environment undergoes. 



Ascending from the visceral actions to the muscular and 

 nervous actions, we find the correspondence displayed in a 

 manner still more obvious. Every act of locomotion implies 



