ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
587 
Fr. Boll, however, nineteen years after them, finding that the rods of 
the retina of the Triton gave inverted images, called in question the 
functional importance of these images, and once more directed attention 
to Muller’s theory. Grenacher followed in the same direction, and 
lastly, Exner proved by Hydrophilus piceus that the image of Gottsche 
cannot be produced in the living animal, for it could not possibly lie in 
the position accorded to it by theory. 
The author’s recent observations were made exclusively on the eye 
of the male Lampyris splendidula. In this there is a fusion of the 
crystalline cones with the cornea, so that it is possible to wash away the 
pigment and the soft parts of the eye, and to examine the whole dioptric 
apparatus in the normal relation of the crystalline cones to the corneal 
facets. The eye was mounted in glycerin of refractive index 1 * 346 
(that of the blood of Hydrophilus piceus ), in such a way that the convex 
cornea was in contact with air, the crystalline cones with a fluid of 
approximately the same refractive index as the glow-worm’s blood. Under 
the Microscope, with low powers, an erect image is seen of an object 
placed between the Microscope mirror and the eye. The sharpness of 
the images given by a fresh eye was extraordinary. A less perfect 
image of an arrow was given by an eye which had been kept in spirit 
4-5 months. It measured O’ 24 mm., while the length of the arrow 
was 32 cm., and its distance from the preparation 52 cm. The distance 
between the ends of the crystalline cones and the retina was determined 
by adjustment of the Microscope to be 0*23 mm. 
When the position of the eye on the stage was inverted, so that the 
concave side was turned towards the object, an image was observed 
which was approximately in the same position as the normal retinal 
image, and had the same magnitude, but was inverted. Numerous 
observations and experiments were made in order to determine the 
path of the rays in the eye necessary for an erect image. 
Directing the Microscope on the centre of the line joining two flames 
and adjusting on the plane of the retinal image, two light* points were- 
seen. By approaching the focal plane towards the cornea it was 
determined that two rays come from each crystalline cone, one from 
the right object-point being deflected to the right image-point, while the 
other from the left object-point is in the same crystalline cone deviated 
to the left image-point. Thus it was found that a ray entering the 
crystalline cone at an angle makes an angle with it on emergence, and 
is on the same side of the axis, and in the same plane. 
Fig. 61 shows the path of the rays for a single light-point at such a 
distance that the rays are approximately parallel, hh represent the 
facets, 0 a to Oh their axes ; the parallel rays are deflected in the 
crystalline cones so as to form the image at B. 0 is the centre of 
curvature of the eye. Similarly an image would be formed of another 
object-point lying for example in the direction O h, and it is clear that 
the total image would be erect. 
Fig. 62 represents the image obtained when the Microscope 
is adjusted on a plane in front of the cornea. This gradually passes 
into that of fig. 63, when the focal plane is moved back until in the 
neighbourhood of the vertices of the crystalline cones. On moving 
the focal plane still further back, the bright circles of fig. 63 become 
