FURTHER REMARKS ON THE COMPOUND EYE. 581 
d. Optical Constants of the Compound Eye of the Blow-fly. 
Constants obtained by calculation have an * prefixed. 
Number of ommatea in each eye - 4,000 to 5,000. 
Radius of curvature of compound cornea : 
Central region - - 2°00 mm. 
Peripheral region - - o'2 mm. 
Angular divergence of adjacent ommatea, from 1° to 6°. 
Corneal lens: 
Diameter - - - ‘025 to ‘03 mm. 
Radius of curvature of anterior sur- 
face (vy) - - - - ‘024 mm. 
Radius of curvature of posterior sur- 
face (s) - - - - ‘or8 mm. 
*Refractive index of entire lens — - 1°65. 
Posterior focus (/) - - - ‘021 mm. 
Magnitude of subcorneal image cor- 
responding to 1° diameter d=/sin. 1°=*000357 mm. 
Anterior focus of rhabdome ~~ - - ‘oo8 mm. 
Length of cone - - - ‘03 mm. 
Length of great rod - . - *200 mm. 
*Estimated magnifying power of rhab- 
dome - - - - X 25. 
*Posterior focus of great rod - - ‘2 mm. 
*Estimated radius of curvature of an- 
terior surface of rhabdome, be- 
tween - - - ‘oor and ‘oo2 mm. 
*Refractive index of the rhabdome, be- 
tween - - - 1°455 and 1°575. 
Diameter of the rhabdome - - ‘006 to ‘oo8 mm. 
Angular measure of Gottsche’s image - 20° to 25°. 
*Angular measure of the smallest dis- 
tance of distinct points in the 
visual perception - - 20. 
(See p. 567.) 
Acuity of vision in man - She Sa" 
