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POPULAR SCIENCE REVIEW. 
Endeavours to test tlie correctness of tMs view failed at first, 
owing to the impossibility of placing under the microscope 
crystalline cones and corneal facets of an eye in tbe normal 
position and under conditions corresponding to those of life. 
Nevertheless, this test could be carried out at least upon one 
animal, and it perfectly confirmed the above view. In the south- 
ern glow-worm (Lampyris splendidula) the crystalline cones are 
amalgamated with the corneal facets. If this eye is separated, 
completely freed from pigment by a hair-pencil, then laid with 
the corneal surface upon a perforated mica object-carrier so that 
the cornea closes the perforation, and then a drop of the beetle’s 
blood is placed in the hollow of the eye, and over this a small 
film of mica, we have imitated as exactly as possible the natural 
conditions as regards refraction and reflection. If we then 
look down through the microscope upon this preparation,* we 
see an absolutely black surface, sprinkled with very bright 
points. The effect is so striking that one cannot help thinking 
that the object has not been freed from pigment. But if we 
turn it so that the light may fall perpendicularly to the axis of 
the cones, these are seen, like the corneae, to be quite glassy and 
transparent, and perfectly free from pigment. This experiment 
shows, in fact, that the rays penetrating into the eye are guided 
by refraction and reflection to the apices of the crystalline cones; 
and that, if we leave out of consideration the small amounts 
that may return through the cornea, these are the only points 
in the whole optical system from which they can issue. There 
is nothing in the shape of a retinal picture in Gottsche’s 
sense. 
Although it may be hoped that Gottsche’s theory is for 
ever disposed of, and that of Johannes Muller reinstated in its 
rights, a new question arises out of this very circumstance, 
namely, how are we to explain the fact that two sense-organs, 
developed for the same outward purpose, show such differences 
of structure as occur in the eye of the vertebrate and the 
facetted eye ? 
TJpon this subject I have also set up an hypothesis. While 
making some physiological investigations upon the seeing of 
movements which, of course, related to the human eye, it struck 
me that the facetted eye was much more advantageously con- 
structed for this special purpose than the vertebrate eye. From 
the important part performed in the animal world by the seeing 
of movements (the evidence of this is in my original memoir) 
it seems really not improbable that in it we have the clue to 
the comprehension of the insect eyes. This is the state of the 
* Of course the plane mirror of the microscope must he employed in 
order to imitate the natural conditions. 
