28 
POPULAR S3IE^X’E REVIEW. 
EXPLANATION OF FIGURES. 
Plate XXXVII. 
Fig. 
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1. Section tlirougli the compound ,^eye of Libelliila : a, cornea, 
continuous with chitin shin of insect; b, layer of ‘‘bacilli” be- 
tween cornea and optic ganglion — radially disposed so as to 
converge from periphery to centre ; c, pigment investing inner 
ends of the bacilli which are continuous with nerve fibres of 
optic ganglion : d, optic ganglion. 
2. Surface view of cornea of Libellula : showing facets (six-sided). 
The division into facets is marked by a deeper-coloured shade, 
which corresponds to a more pigmented and denser portion of 
corneal substance. 
3. Cornea with subjacent stratum of “bacilli” of Libellula : a, the 
exterior corneal surface shows lenticular facets ; b, vertical lines 
indicating tlie division of corneal substance (through its thick- 
ness) into constituent portions corresponding in width to that 
of the facets on its surface ; c, pigment investing outer ends of 
“ bacilli ” (d) which are enclosed in sheaths (see fig. 4) ex- 
tending from inner surface of cornea to surface of op tic ganglion; 
c, pigment investing inner ends of bacilli. 
4. Two bacilli, composed of sheaths of membrane enclosing nerve 
substance, the outer swelling of which corresponds to the 
“ crystalline body ” of authors. To examine the bacillar struc- 
ture under the microscope, solution of caustic potash must be 
used to dissolve the pigment. 
5. Section across the bacilli (horizontal section), showing the circular 
outline of the sheatlis, which are coated with pigment. The 
clear lumen within is occupied by nerve substance of bacilli. 
G. Vertic.al section of cornea and bacillar stratum of Libellula : a, 
outside corneal surface (curved facets) ; 6, inner corneal surface 
forming a plane curve — vertical lines through the thickness of 
cornea between the “ corneules ” — horizontal lines are more 
faintly perceptible, showing a disposition of the substance in 
zones or laminm ; c, on the right side of fig, 6, the membranous 
sheaths are shown w’ith their contents — nerve and crystalline 
body ; d, on the left side the sheaths are shown empty. The 
outer and inner ends of three sheaths (the middle portion having 
been cut away in the preparation) are seen attached to inner 
conical surface and outer surface of optic ganglion ; c e, optic 
ganglion — a tracheal tube runs ccncentric with its outer border; 
/, fibres of optic nerve. 
7. .Siinjde eye of Salticus icneus. Vertical section show'ing a, cornea 
and lens formed by thickening of laminm of conical substance ; 
b, zone of pigment round the lens ; c, choroid pigment ; d, the 
“corpus vitrium ” of J. Muller (the bacilli of Lcydig continuous 
with); fi, nerve fibrils ; /, retinal cells. 
