81 



cluunber is extensive but incapaciuus and completely separates the eyeball, which 

 is formed by the optic vesicle and the iris, from the capsule of the eye. The 

 chamber communicates witli the exterior tlnu a small canal, the "aquiferous 

 pore", which is sunounded by a sphincter muscle and which has at its inner 

 end a ciliated funnel composed of columnai- cells. This pore lies at the ventral 

 edge of the eye just in front of the cornea. The capsule is helmet-shaped and is 

 attached to the margin of the optic cup of the skull. It is composed of connective 

 tissue, muscle and skin. The outer wall of the capsule covers almost all of the 

 side of the true liead and contains the cornea, a circular, transparent, slightly 

 convex membrane whose margin is supported by a ring of stiff connective tissue. 

 The inner wall of the capsule separates the outer chamber of the eye from the 

 sac which contains the peduncle of the tentacle. The capsule is lined by a pave- 

 mental epithelium except in the neighborhood of the aquiferous pore and is 

 reflected over the iris , forming the only connection between the capsule and 

 the eyeball. 



The iris is a thick , opaque , iridescent curtain which projects from the 

 margin of the sclerotic cup into the outer chamber of the eye. A small visor-like 

 fold of the iris projects into the pupil from its upper margin and by a contrac- 

 tion in faint , and extension in strong light , alters the shape of the pupil from 

 a circular to a cresentic form and so adjusts the illumination of the retina. The 

 iris has four layers : - an outer epithelium , a, thick argentea , a muscular layer , 

 and an inner epithelium. The outer epithelium is pavemental and is continuous 

 with that lining the capsule. The argentea is a thick , opaque coat and extends 

 beyond the iris over all the eyeball except the dorso-internal surface which is 

 in contact with the optic ganglion. The opacity and iridescence of the argentea 

 are due to a vast number of rods and fibres which interfere with and reflect 

 light. The cells which produce these rods and fibres are similar to the iridio- 

 cysts of the skin. The protoplasm of each cell produces a large number of rods 

 or fibres , as the case may be , there being left barely enough untransformed 

 material to hold the rods or fibres together. All the rods or fibres produced by 

 a cell are parallel but the fibres of different cells are inclined to one another at 

 various angles. The cells immediately beneath the outer epithelium produce 

 short r(xls that are perpendicular to it. The fibres of the underlying cells tend 

 to lie parallel to the epithelium or to foi'm acute angles with it. The impor- 

 tance of the argentea is evident since all the tissues of the living squid except 

 this and the iridiocysts are very translucent, almost transparent, and without 

 the argentea the posterior chamber of the eye would be penetrable by light 

 rays from all directions. The muscular layer of the iris is formed of circular 



