ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
589 
is formed between the focus on the hinder part of the crystalline cone and 
its vertex, so that the rays m, n from on leaving the cone, are slightly 
divergent. Thus a x b x gives rise to the virtual image a 2 b 2 . The figure 
shows how the angle of emergence of a pencil to the axis is on the same 
Fig. 62. 
Fig. 63. 
Fig. 64. 
Fig. 65. 
side as the incident pencil, and that it is so much greater, as the incident 
angle is greater. The author has constructed a model of an insect eye 
on the above principles. It consists of ten pairs of convex lenses, each 
of focal length of 2 in. The two members of each pair are separated by 
