588 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
narrower, and finally the image shown in fig. 64 is obtained. Fig. 65 
shows the appearance when the focal plane is behind the retinal 
image. 
The author’s experiments lead to the conclusion that the dioptric 
apparatus of the Lampyris-eye is very similar in its effects to a system 
of two lenses on the same axis which are separated by a distance equal 
to the sum of their focal lengths. In the Lampyris-e ye the two convex 
lenses are replaced by two cylindrical lenses, the Linsencylinder of 
Exner, which form the crystalline cone. The path of two pencils in 
a crystalline cone, according to this principle, is shown in fig. 66. 
The inverted image a 2 b 2 of the distant object a b , which gave rise to so 
much confusion in the physiology of the compound eye, is formed not at 
the vertex or behind the cone, but in front, where there can be no nerve- 
fibres. The rays m and n proceeding from a form an image at a x ; 
similarly the rays p and q from b form an image at b y The image a x b x 
