EXPLANATION OF PLATES I & II, 



Illustrating Mr. Sydney J. Hickson's Memoir on the 

 '* Eye of Pecten/' 



Fig. 1. — A diagrammatic sketch of an eye of Pecten maximus. a. The 

 cornea, b. The transparent basement membrane supporting the epithelial 

 cells of the cornea, c. The pigmented epithelium, d. The lining epi- 

 thelium of the mantle, e. The lens. /, The ligament supporting the lens. 

 g. The retina, h. The tapetum. k. The pigment. /. The optic nerve. 

 m. The retinal nerve, n. Complementary nerve, p. The circumpaleal 

 nerve (Duvernoy). q. A supplemental nerve from pedal ganglion. 



Fig. 2. — Epithelial cells of cornea. 



J'kj. 3, — Section through the junction of the pigmented epithelium with 

 corneal epithelium. 



Fig. 4, — Vertical section through eye of Pecten maximus. «, b. Cornea. 

 c. Pigmented epithelium, d. Mantle epithelium, e. Lens. g. Retina. 

 h. Tapetum. h. Pigment. /. Section of optic nerve. 



Figs. 5, 6. — Isolated rods. 6«. — Diagrammatic- sketch of a central 

 rod. p. I. Posterior limb. m.p. Membrane pierced by rods. a. I. Anterior 

 limb. s.r. Spindle-shaped portion of rod. n. Nerves. 



Figs. 7. — Transverse sections through eye of P. maximus. a. Rods in 

 section, b. Tapetum. c. Pigment, d. Retinal nerve. 



YiG. 8. — Yertical section of the eye of Pecten maximus, showing the 

 nerve dividing into retinal and complementary branches. 



Fig. 9. — Vertical section of the eye of Pecten maximus, showing the 

 termination of the retinal nerve. The retina has dropped out, and the 

 frayed-out end of the nerve remains. 



Fig. 10. — Section of eye of Pecten o'percularis. 



Fig. 11. Retina {a) of P. opercularis, (b) oi P.jacobaus, (c) P. maximus. 



j^ote. — A horizontal section means a section made in the same plane as 

 the mantle. A transverse section, in a plane at right angles to the eye 

 stalk. A vertical section, in a plane at right angles, both to the plane of the 

 mantle and the last-named plane. 



