TBE EYE OP PECTEN. Ill 



Muscles of eye-stalk. M. Ret. Mai-ginal area of retina. N. Lf. Nuclei 

 of muscle-fibres of lens sui-face. nuc. Niicleus. 0. I. c. Outer inter- 

 stitial cells. Oj9. D. Distal branch optic nerve. Op. Ds. Slieath of 

 distal nerve. Op. N. Optic nerve. 0}^. P. Proximal liranch optic 

 nerve. Op. P''. Fibres (separated) of proximal branch of optic nerve. 

 P. man. Pigment-mantle. Pg. Pigment-layer. E. C. Rod-cells. 

 R. C. n. Nuclei of rod-cells. R. mat. Rod-matrix. Rod. Rod. S. m. 

 Pseudo sieve-membrane (see text). Sc. Modified connective-tissue wall 

 of optic vesicle. Sep. Septiim. Ta. Tapetum. ta. c. Pigment layer 

 concretion. V. Velum. 



PLATE 6. 



Fig. 1. — Section through eye-stalk and eye, P. maxim us, in a plane 

 at right angles to that of the mantle surface ; the right side of the 

 figure represents the shell side of the eye. The various parts, lens, 

 retina, etc., have been drawn with the camera lucida, but from different 

 pi-eparations, each showing Ijest the part drawn, x 270. 



PLATE 7. 



Fig. 2. — Diagrammatic section through both mantle-lol^es of P. 

 jacobseus, illustrating the course of the nerves and difference in size 

 of the eyes. The left mantle-lobe is to the left in the figure. 



Fig. 3. — Upj)er surface of cornea, P. maxim us. x 1000. 



Fig. 4. — Transverse section of coi-neal cells at about the middle of 

 their height. P. maximus. X 1000. 



Fig. 5. — Isolated cells from the lens. P. maximus, maceration in 

 chloral hydi-ate solution, x 570. 



Fig. 6. — Lens-cells as seen in sections. h. Normal cells from 

 Hermann-sublimate fixed specimen, P. varius. a. Cell from same 

 specimen with large nucleiTS. Stain iron hsematoxylin. d. Cell from 

 lens fixed in von Rath's fluid, x 660. 



Fig. 7. — Transverse section cutting layer of filjres between lens and 

 subcorneal tissue. The fibres and cells are stained red with Mallory's 

 connective-tissue stain, the subcorneal tissue blue. P. tenuicostatus. 

 X 310. 



Fig. 8. — Filjres between lens and subcorneal tissue ; attached to the 

 latter in a maceration preparation (chromic acid). P. jacobseus. 

 X 300. 



Fig. 9. — Cells and nuclei between lens and subcorneal tissue, as seen 

 through the cornea, which has been teased from an eye fixed in Zenker's 

 fluid. Iron hsematoxylin. P. maximus. x 330. 



