NOTES ON BETTEEFLIES. 
55 
Some butterflies have, at the angles joining these hexagonal 
facets, a hair standing out, which, repeated at thousands of 
such angles, gives to the eye a rough or hairy look. Such 
hairy eyes are represented at No. 2. They are very dark. It 
is in these eyes difficult to see anything but the clothing of 
hairs. 
But other butterflies, such as the white ones, have no hairs 
in the eye. The eye is then quite smooth and transparent, as 
at No. 3. Holding such a butterfly closely, with its head 
turned sideways to the sunlight, a very lovely picture is seen 
displayed, of an arrangement such as is figured at L, of dark 
hexagonal spots divided by a network of light-coloured lines. 
This is brilliantly lit up, and is exactly in appearance like the 
effect produced by those glass paper-weights which have a 
picture inside them, magnified by the round surface of the 
enclosing glass. 
The most convenient fly to see this in is the small cabbage 
one, for it is more easily caught than the larger white. This 
the writer found from having told his little boy to catch some 
white butterflies in the kitchen-garden. He always brought 
in the smaller white, saying that the others were too quick for 
him. On seeking a reason for this slowness of sight, it is 
found that the smaller white has the upper part of the eyeball 
clouded with an opaque shading, as at p Q, which prevents it 
seeing anyone approach just above it, though leaving the sight 
clear at the sides. 
Taking this conveniently blind little fellow, then, as the 
subject of examination, easily renewed, the theory of explana- 
tion of this appearance evidently is this : — 
The hexagonal network on the surface of the eye, as at No. 1 , 
is reflected down on the interior retina in its very small natural 
size. Then the whole outer surface of the eye, considered as 
one surface, acts like a globular lens, magnifying the interior 
reflection till it is easily discerned with the observer’s unaided 
eye, and assumes the very beautiful, picture-like appearance 
which lasts while the eyes are fresh and moist. Thus the 
butterfly’s eye is a natural magnifying glass, exactly like what 
is known as a Stanhope lens. The observer uses it as at u, and 
sees the cells much enlarged. 
That the hexagonal appearance is not exactly the same in 
outline as the actual network on the cornea of the eye is due to 
the fact of the retina upon which the reflection is cast not being 
exactly in the focus of the curved lens surface. This leads to 
an overlapping of the outlines of the facets, making them seem 
much thicker than the dividing lines between the facets of the 
surface really are, as at fig. o. 
The proboscis or trunk of the butterfly next claims attention. 
