PEESENCE OF EYES IN SHELLS OE CEETAIN CHITONIDiE, 15 
The ouly pigment present in thè eyes examined is that by 
which thè eye capsules are rendered opaque. No pigment seen 
in connection with thè rods or in connection with thè nervous 
elements. Possibly thè absence of such pigment is due to thè 
imperfect preservation of thè material. 
Not all thè fibres of thè strand entering thè eye cavity 
proceed to thè retina. A large number of peripherally placed 
fibres pass outside thè retina all round, and, passing through 
apertures in thè iris at its outer margin, end at thè surface of 
fhe shell all round thè area occupied by thè corneae. They 
terminate in micrsesthetes exactly corresponding in structure 
to thè other micraesthetes present and identical with them in 
structure. 
They apparently form a sensitive zone round each eye, and 
their strands arise from thè optic nerve just as do those of many 
of thè other micraeesthetes from thè megalaesthetes (see PI. VI, 
fig. 6, V h' -, fig. 4, 6; PI. V, fig. 8, b' V). On their way to thè 
surface these strands, given off by thè optic nerves to thè 
micraesthetes, traverse a series of slit-like perforations of thè 
ris, which are conspicuous, and at first very puzzling features 
in thè iris structure when thè eyes are viewed in thè decal- 
cified tegmentum from its external surface by transmitted 
light (PI. VI, fig. 5, 5 ò). 
In thè eyes of some forms when thus viewed, an open fold 
or gutter leading from thè bulb superficially along thè stalk 
of thè pear is seen, curiously recalling thè choroid fissure 
(PI. VI, fig. 5). The occurrence of doublé eyes, combinations 
of two eyes fixed closely side by side with a common nerve 
stalk, is not an uncommon mode of growth. 
Growth of thè Tegmentum, Eyes and ^Esthetes. 
The tegmenta increase in growth by additions formed at 
their margins where they adjoin thè girdle regions of thè 
mantles. The additions are probably made by thè mantle 
tissues which immediately abut on thè tegmental margins. 
At thè basai margins of thè tegmenta of all forms in which 
