506 The Structure of the Eye of Trilobites. [July, 
eye has been broken into two, the conical lenses are seen to 
extend through the cornea as cup-shaped or conical bodies, and 
are quite distinct from the cornea itself. In another broken eye 
of the same species, the cornea is partly preserved, and two of the 
corneal lenses are seen to extend down into and partially fill two 
hollows or pits; these pits are evidently the impressions made in 
the fine sediment which filled the interior of the molted eye or 
cornea ! 
Thus in the Asaphus gigas noticed above, we have the entire 
inside of the cornea with the cone-like lenses projecting from the 
concave interior; while in the last example we have the impres- 
sions made by the cones in the Silurian mud which silted into the 
cornea after the trilobite had cast its shell. 
Farther evidence that the trilobite’s eye was constructed on the 
same pattern as that of the living horse-shoe crab is seen in the 
sections made by Mr. Walcott. We will first describe, briefly, 
the eye of Limulus. Fig. I 
represents a section through 
the cornea of Limulus; c, the 
cornea, which is seen to be a 
thinned portion of the integ- 
ument; fc, indicates one of 
the nutrient or pore canals, 
which are filled with connec- 
tive tissue extending into the 
integument from the body 
cavity; c/, is one of the series 
of solid conical corneal lenses. 
These are buried partly in the 
black retina, and the long 
\—" slender optic nerve just before 
Fic, 2,—Section through the eye of a tril- f eaching the eye subdivides, 
obite; lettering as in Fig. 1. 50 diams. sending a branch to each facet 
or cornea, impinging on the lens. Fig. Iæ represents a vertical 
view of the corneal lenses or facets, magnified fifty diameters, aS 
seen through the transparent cornea. It will be seen that they 
are slightly hexagonal and arranged in quincunx order ; their 
external surface is flat, though that of the ocelli is slightly 
convex. 
Now if we compare with the horse-shoe crab's eye that of the 
