GENERAL RESULTS. 303 



The results arising from these facts are not confined to 

 animal Physiology; they give information also regarding 

 the condition of the ancient Sea and ancient Atmosphere, 

 and the relations of both these media to Light, at that re- 

 mote period when the earliest marine animals were fur- 

 nished with instruments of vision, in which the minute 

 optical adaptations were the same that impart the percep- 

 tion of light to Crustaceans now living at the bottom of the 

 sea. 



With respect to the waters wherein the Trilobites main- 

 tained their existence throughout the entire period of the 

 Transition formation, we conclude that they could not have 

 been that imaginary turbid and compound Chaotic fluid, 

 from the precipitates of which some Geologists have sub- 

 posed the materials of the surface of the earth to be de- 

 rived ; because the structure of the eyes of these animals is 

 such, that any kind of fluid in which they could have been 

 eflicient at the bottom, must have been pure and transparent 

 enough to allow the passage of Hght to organs of vision, the 

 nature of which is so fully disclosed by the state of perfec- 

 tion in which they are preserved. 



With regard to the Atmosphere also we infer, that had it 

 diflfered materially from its actual condition, it might have 

 so far affected the rays of Light, that a corresponding dif- 

 ference from the eyes of existing Crustaceans would have 

 been found in the organs on which the impressions of such 

 rays were then received. 



Regarding Light itself also, we learn from the resem- 

 blance of these most ancient organizations to existing eyes, 

 tiiat the mutual relations of Light to the Eye, and of the 

 Eye to Light, were the same at the time when Crustaceans 

 endowed wdth the faculty of vision were first placed at the 

 bottom of the primeval seas, as at the present moment. 



Thus we find among the earliest organic remains, an 

 Optical instrument of most curious construction, adapted to 

 produce vision of a peculiar kind, in the then existing repre- 



