1886. | Microscopy. QI 
but can be restored by keeping the insect in the dark for half an 
hour. The disappearance of the reflex in the light is due to the 
contraction of the pigmented iris cells. 
METHOD oF ISOLATING THE DIOPTRIC LAYERS OF THE CoM- 
POUND Eyvr.—Gottsche’ was the first who succeeded in isolating 
the whole dioptric portion of the compound eye, so that the cor- 
neal facets and the cones could be examined zz sítu. The isola- 
tion of the corneal layer alone is more easily effected; this had 
already been accomplished by Leeuwenhoek, Baker, Brants and 
Gruel, who examined with the microscope the images produced 
by the corneal facets. 
Gottsche took the eye of a fly, and separated the inner wall, so 
that only the cornea with the optical apparatus remained. Hold- 
ing the cornea fast by one end, he next removed the red portion 
of the eye, z.¢, the retinule. These break off at the inner ends 
of the cones, leaving the cornea with the cones intact. The 
preparation is next laid on a slide with the convex side of the 
cornea down (there should be just glycerine enough beneath the 
cornea to make it adhere to the slide). A cover-glass is then 
placed over the preparation, with care to leave the concave upper 
side filled with an air-bubble. Slight pressure on the cover-glass 
will usually be found sufficient to create the air-bubble. If no 
undue’ pressure has injured the cones, the preparation is now 
ready for examination with the microscope. The tube of the 
microscope may now be placed so that the hexagonal facets are 
in focus, and then raised until the inner (upper) ends of the cones 
become visible, but not sharply focused. If any object, e.g., a 
Steel pen, is now held between the mirror and the preparation, a 
minute inverted image of the same will be seen in each facet. 
Grenacher thinks the contents of the cones (“ pseudocones”) 
wouid escape by Gottsche’s method, so that the experiment would 
really amount to no more than that of Leeuwenhoek, Baker, &c. 
Grenacher (Das Sehorgan d. Thiere, p. 148), taking the eye 
of acrepuscular or nocturnal moth that had been hardened in 
cohol, cuts off a section with a sharp knife, places it on a slide 
with the convex corneal surface below, and then removes the pig- 
ment by a careful use of nitric acid. With this preparation he 
repeats the experiment of Gottsche, and finds that the images fall 
not behind nor in the ends, but near the middle of the 
cones. This position of the images, at points where there are 
no percipient elements, is held by Grenacher to be fatal to the — 
view that they are seen by the insect. According to Lowne’s’ 
view, the retinula constitute a second refractive system which > 
Serves to magnify and erect the images formed within the cones,  — 
So that the whole visual field consists of a mosaic of erect images. 
, Mill. Arch., 1852, p. 488, 489. 
. Trans. Linn. Soc. Lond., p. 389. Dec., 1884. 
