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 i to 6. 

 Corneal lens : 



Diameter - -025 to '03 mm. 



Radius of curvature of anterior sur- 

 face (r) - -024 mm. 

 Radius of curvature of posterior sur- 

 face (s) - -018 mm. 

 *Refractive index of entire lens 1*65. 



Posterior focus (/) - '021 mm. 



Magnitude of subcorneal image cor- 

 responding to i diameter d=fsin. i = "000357 mm. 

 Anterior focus of rhabdome 

 Length of cone 

 Length of great rod 



*Estimated magnifying power of rhab- 

 dome 



* Posterior focus of great rod 



*Estimated radius of curvature of an- 

 terior surface of rhabdome, be- 

 tween 



*Refractive index of the rhabdome, be- 

 tween 



Diameter of the rhabdome 

 Angular measure of Gottsche's image - 



* Angular measure of the smallest dis- 



tance of distinct points in the 

 visual perception - 20' 



(See p. 567.) 



*oo8 mm. 

 03 mm. 

 200 mm. 



X 25. 



2 mm. 



ooi and '002 mm. 



1-455 and 1-575. 

 006 to '008 mm. 

 20 to 25. 



Acuity of vision in man 



._ 



60 



