248 
INTRODUCTION. 
rcous humor ; but the character of the retina I did not 
detect at the time. Whether a crystalline lens exists or 
not I am in doubt ; at the time of making the investiga- 
tions, in several instances I thought I discerned it very 
distinctly ; but in other instances, even when larger spe- 
cies were examined, if it existed it escaped my observa- 
tion. 
