15 
limuli, in the regions of Europe which now 
form the elevated plains of central Germany. 
“ 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 re¬ 
lations of both these media to light, at that re¬ 
mote period when the earliest marine animals 
were furnished with instruments of vision, in 
which the minute optical adaptations were 
the same that impart the perception of light 
to crustaceans now living at the bottom of the 
sea. 
“ With respect to the waters wffierein the 
trilobites maintained their existence through¬ 
out the entire period of the transition forma¬ 
tion, we conclude that they could not have 
been that imaginary turbid and compound 
chaotic fluid, from the precipitates of which 
some geologists have supposed the materials 
of the surface of the earth to be derived ; be¬ 
cause the structure of the eyes of these ani¬ 
mals is such, that any kind of fluid in which 
they could have been efficient at the bottom, 
