178 PROCEEDINGS OF SOCIETIES. = [ Monthly, Microscopial 
a mechanical or physical office, its office is vital or mental. He 
thought it necessary to dwell longer on the compound eye of the 
invertebrates, as our knowledge of its structure is still imperfect. 
Little advance had been made for 200 years, until the German phy- 
siologists lately showed that the eyes of insects and crustaceans— 
with a common function—present many analogies with those of verte- 
brates. 
Dr. Hallifax exhibited diagrams of the eye of the dragon-fly, and 
pointed out the bulbed ends of the nerve fibres, which are not, as has 
been supposed, crystalline lenses, but true representatives of the rods 
and cones of the baccillary layer of the retina—the percipient element 
of the eye. 
These bulbed nerves are each’ covered with pigment, except that 
where they come in contact with the lenses, there are apertures in 
analogy with the vertebrate pupil. 
The lenses are the outer hexagonal facets, each a double convex 
lens of itself, the inner surface the most convex, and placed in contact 
with a bulbed nerve—each with its independent nerve forming a dis- 
tinct eye. The facets in the compound eyes of insects can be num- 
bered by hundreds ; but as with the human eyes the two images are 
perceived as one, so the mental perception of the fly recognizes but a 
single object. 
Dr. Hallifax called attention to the absence, in the eyes of insects, 
of the crystalline lens and vitreous humour of the vertebrates, although 
the essential lens and cones are represented. 
The numerous facets of the eyes of insects allow, from their posi- 
tion, of extreme range of vision, and render unnecessary the powerful 
muscles of the vertebrate eye. 
Dr. Hallifax considered the eyes of insects most fitly placed and 
formed, with reference to their organization generally, and said that 
we should always consider organs with such reference to general 
structure. 
He then exhibited, under the microscope, beautiful sections of the 
eyes of insects, in demonstration of his subject. 
In the discussion which followed, Dr. Hallifax was asked his 
opinion of the structure of the single eyes placed between the com- 
pound eyes of flies, and on spiders, as they appear to present a much 
closer approach to the vertebrate type than is allowed to the com- 
pound eyes. Dr. Hallifax explained that he accepted the authority 
of those who consider the spherical portion at the back of such single 
eyes as an enlargement of the cornea, and not a vitreous humour ; he 
did not, however, extend his explanation to the arrangement of lenses 
and iris shown in one of his own sections of a spider’s eye, and which 
seems almost identical with that of the human eye. 
After a vote of thanks was passed to Dr. Hallifax, it was an- 
nounced that the next Field Excursion would be to Lewes, on Saturday, 
September 8rd; that the Microscopical Section would meet on August 
25th—subject, Mounting Objects; and that the meeting of the Society 
on September 8th would be the Special Annual Meeting, for the 
election of officers, &e. 
