PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONID.E. 59 
PLATE VI. 
Fig. 1. — Sketch of a lateral view of a specimen of Acanthopleura 
spiniger. x. Small area on the side of the tegmentum of one of the middle 
shells, which is shown more highly magnified in Fig. 2. 
Fig. 2.— The area indicated in the foregoing figure enlarged 65 diameters. 
a a. Prominent rounded tubercles on the shell surface, b b. Pore-hillocks, 
each with a megalopore visible at its summit, d d. Eyes. 
Fig. 3. — Three of the pore-hillocks of Acanthopleura spiniger shown 
in the preceding figure more highly magnified, a. Megalopore. b. Micro - 
pore. 
Fig. 4. — View of the surface layer of the soft tissues of a decalcified middle 
shell of a species of Acanthopleura from China, viewed by transmitted light, 
showing the grouping of the micrsesthetes and megalsesthetes in relation with 
an eye. The cuticula of the tegmentum is seen to be finely fibrous, n. Chan- 
nel, containing the optic nerve. 1. Lens of the eye. ch. Pigmented eye- 
capsule, forming an iris-like border around the lens. b. Tips of micrsesthetes, 
which pierce the iris and terminate at the free surface of the shell around the 
margin of the cornea, a a a. Macrsesthetes in chambers, hollowed out in 
the tissue and continued in the direction of the margin of the shell which 
adjoins the girdle into nerve canals. 
Fig. 5. — A single eye of Schizochiton decalcified. 1. Lens. ch. Pigmented 
eye-capsule, continued inwards to form an iris, b b. Slit-like apertures in 
the iris, giving passage to the branches given off by the optic nerve to the 
ocular micrsesthetes. s. Cleft in the outer wall of the channel for the optic 
nerve. 
Fig. 6. — Schemalic representation of the structure of the soft and some 
of the hard parts in the tegmentum of a shell of Acanthopleura spiniger, 
as seen in a section vertical to the surface and with the margin of the shell 
bordering on the girdle lying in the direction of the left side of the drawing. 
f. Calcareous cornea. h. Iris. g. Lens. k. Pigmented capsule of eye. 
n. Optic nerve, r. Rods of retina, n! . Branches of the optic nerve, per- 
forating the capsule wall and terminating in b' b' b'. Ocular micrsesthetes. 
p p. Nerves to macrsesthetes. m. Body of macrsesthete cut across, o e. Fusi- 
form body of macrsesthete entire, a. Obconical termination of macrsesthete. 
e. Nerve given off by macrsesthete to micrsesthete b" . 
Fig. 7. — Rods of the retina of Acanthopleura spiniger, viewed from 
above in a horizontal section of the eye. 
Fig. 8. — Sketch of a specimen of Acanthopleura piceus, viewed from 
the side, of natural size. x. Area on the side of the tegmentum of one of the 
middle shells, which is seen highly magnified in Fig. 9. 
Fig. 9. — The area indicated in Fig. 8, enlarged 26 diameters. The lateral 
