16 
must have been pure and transparent enough 
to allow the passage of light to organs of 
vision, the nature of which is so fully dis¬ 
closed by the state of perfection in which 
they are preserved. 
“ With regard to the atmosphere also we in¬ 
fer, that had it differed materially from its ac¬ 
tual 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 or¬ 
ganisations to existing eyes, that the mutual 
relations of light to the eye, and of the eye 
to light, were the same at the time when 
crustaceans endowed with the faculty of vision 
were first placed at the bottom of the prime¬ 
val 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 representa- 
