208 RAMBLES AND REVERIES. 



trilobite, so far as physical conditions are concerned, 

 did not greatly differ from what we now see in 

 natnre. These primeval seas and the atmosphere 

 above them acted as media of light, just as water 

 and air now do. The Limulus or King-crab has 

 compound eyes that bear the same relationship to 

 light as did those of the trilobite, and the same 

 optical laws were evidently in operation. To quote 

 again from Dr. Buckland's Bridgewater Treatise, 

 " The earliest marine animals were furnished 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 regard to the atmosphere, we 

 infer that had it differed materially from its actual 

 condition, it might have so far affected the rays of 

 light that a corresponding difference 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 resemblance of these most ancient 

 organizations to existing eyes, that the mutual 

 relations of light to the eye, and of the eye to the 

 light, were the same at the time when crustaceans 

 endowed with the faculty of vision were first placed 

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

 moment." 



Having dealt with the geological distribution of 

 trilobites and their structure and classification, it now 

 only remains to consider the question of their descent. 



Whatever may be thought of the evolution theory 

 as an explanation of the mode of creation, the efforts 



