18 
OcTOBER 24th, 
MICROSCOPICAL MEETING; DR. HALLIFAX ON THE 
INVERTEBRATE EYE. 
When requested to introduce the subject of the Invertebrate Eye, 
between which and the vertebrate eye were great points of dissimi- 
larity, he thought, from having made many sections for his microscope of 
the eyes of insects and crustaceans, he might be able to direct the 
minds of some of his hearers to a very interesting question,—-viz., 
the tracing out a unity of plan where there appeared to be a diversity 
of structure so striking. 
Thus, whateve1 the organ we investigated in any class of the animal 
creation, it should be compared with the same organ in other animals, 
in order to show their connection by some general plan of unity. As 
an example of what might be deduced by comparison, he might men- 
tion what Mr. Wonfor, by studying the scales of butterflies, had 
deduced. He found certain scales, called battledore and tasselled 
scales, only on the males of certain butterflies, and, pursuing the plan 
of comparison, had arrived at the general law that the butterflies on 
which these scales were found were invariably males. 
It was a strong incentive to enquiry, when we saw any particular 
organ devoted to the same evident purpose, but differing in apparent 
structure, to try and bring it in harmony with the general law of unity 
of plan. In the invertebrates, taking the eye of the dragon-fly asa type, 
was an apparent divergence, as wide as possible, from the highest type 
of the vertebrate, the human eye. 
Comparing them side by side, we found in the first a great mass of 
optic ganglia proceeding from the cephalic ganglia (the equivalent of 
brain in the vertebrates), subdivided and covered with pigment, giving 
off nerves, covered also with a dark pigment, changing into a trans- 
parent substance terminating in a curved surface, which abutted on a 
cornea composed of numerous facets, 4, 5, and 6-sided, but each con- 
sisting of a lens, convex externally and internally. Each of these 
facets, or convex lenses, was capable of bringing the rays of light into 
a focus upon the transparent pigment-covered substance, consisting of 
transformed nerve matter. 
In the vertebrate eye we had a globe filled with vitreous matter, a 
crystalline lens, and aqueous matter, refracting the rays of light, and 
causing them to fall on the nervous matter, called the retina, lining the 
