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the perforation, the portion of membrane which closes the per- 
foration within can receive light only from a very limited direc- 
tion. This direction is different for each perforation. If we 
draw the rays for the individual points of the object which 
run in the axis of the perforation, we see that they must pro- 
duce an erect picture of it upon the supposed membrane. In 
reality, however, no membrane, in the ordinary sense of the 
word, is stretched over the inner apertures of the perforations, 
but the nervous elements, which in combination certainly form 
the retina, are implanted in the inner parts of the perforations. 
From this we see at once that the facetted eyes of the two 
sides of an animal must command nearly the whole space 
around it ; for each eye, by means of its curvature, commands 
more than the half of all possible directions, and the two eyes, 
in consequence of their position, reciprocally complete each 
other. A portion of any object at any time in the field of 
vision is simultaneously seen by both eyes. We see further 
from the imaginary picture above given, that the retinal 
picture, when compared with that of the vertebrate eye, 
will leave much to be desired in the matter of sharpness ; that 
the sharpness will increase with the number of facets that come 
on the hemisphere ; but that the strength of illumination of 
each retinal element will diminish as the number increases. 
As regards the corneal facets and crystalline cones, these, 
according to Johannes Muller, produce no change in the nature 
of the eye, but rather serve only to increase the brightness of the 
whole picture. 
This was the position of matters until the year 1852. 
Gottsche* * * § then remarked that in the eye of a fly which had been 
freed from pigment by means of a cataract needle, a great 
number of minute pictures of external objects, showing con- 
siderable sharpness, could be detected under the microscope, f 
Each of them, was situated over a facet of the cornea (the light 
coming from below towards the convexity of the cornea). 
These pictures were reversed. Gottsche thought at once that 
he had discovered the analogy with the eye of the vertebrate ; 
each facet produced a retinal picture just like the vertebrate 
eye ; but man had only two, and the fly several hundred eyes. 
A note of Johannes Muller’s, appended by him to Gottsche’s 
Memoir, appears to have been drawn up as if he agreed with 
Gottsche’s ideas. In subsequent years a great number of 
authors, and among them LeydigJ and Max Schultze,§ gave up 
* Muller’s Archiv, 1852. 
t These pictures were previously known to Leeuwenhoek. 
X Das Auge der Gliederthiere , 1864. 
§ Untersuchungen iiber die zusammengesetzten Augen der Krebse und 
Insekten, Bonn, 1868. 
