750 William Patten 



harder, outer portion, or lens, l. AX x. one sees a layer of minute, 

 lightly stained bodies whicli may represent the swollen outer ends of the 

 retinophorae (fig. C7). 



Fig. fJ9. A constructed drawing of an ommatidium from the faceted ej^e of 

 Arca Noae. One sees the double retiuopliora, containiug tvvo nuclei, and 

 bearing two rods provided with a network of external nerve fibres, some 

 of wliich form distinct, external loops, ex.f., as \n Pecten. At the base 

 of the celi are the refractive globules, ag., forming an argentinula; within 

 the celi, the axial nerve fibres, ux.f. The retinulae of the inner row are 

 continued outwards as hyaline membranes, rt.s., to form a retinidial 

 sheath. The retinulae of the outer row are continued inwards as color- 

 less stalks or bacilli, bc. 



Fig. 60. An isolated retinula from the inner row, showing its colorless Prolong- 

 ation, rt.s., and the system of external nervo fibres, n.f., with which it 

 is covered. The sj'Stem of lateral fibrillae, similar to those seen on fig. 03, 

 has not been represented by the lithographer. 



Fig. Gl. A fragment of the retinidium, fig. 63, x., more highly magnified, and 

 showing the continuity of the ultimate fibrillae. 



P"'ig. 02. Au isolated retinula from the retineum oi Haliotis. Cam. H. obj. 7,oc.lII. 



Fig. 03. The outer end of a retinula oi Haliotis; the cuticular substance of the 

 rod has been dissolved by treatment with glycerine and bichromate of 

 potash, leaving the entire system of nerve fibrillae intact, x.; the fibrillae 

 of the remainiiig nerve brauches bave not been represented. The length 

 of the unbranched nerve stalks has been, for convenicuce, reduced to 

 one half. 



Fig. 64. A portion of the epithelium from the mantle edge oi Arca barbuta, show- 

 ing the extension of some of the larger nerve branches n.f. to the very 

 outer surface of the cuticula ; the lateral fibrillae of these nerves may also 

 be seen. Cam. obj. 20, Leitz, oc. 111. 



Fig. 05. The inner end of a bacillus, belougiug to a retinula of Haliotis (compare 

 fig. 68 bc], surrounded by several nerve branches, n.f., ali of which are 

 not represented in the figure. 



Fig. 60, Au isolated retinophora [Haliotis] with the two nuclei n.rf.'^ and n.rf.'^; 

 a remarkably instrxxctive preparation since in this iustance the outer end 

 of the cells is divided into two stalks , x. , which represent the imfused 

 ends of the two primitive cells, by the union of which the retinophora 

 was formed ; the body of the celi contains many refractive globules, ay., 

 similar to those which form the argentinula inarca. Cam. obj. 20, Leitz, 

 oc. III. 



Fig. 67. The most common form of retinophora , from Haliotis, containing two 

 nuclei, but with the outer end of the celi single instead of double. Cam. 

 obj. 20, Leitz, oc. III. 



Fig. 68. Two retinulae from the retina oi Haliotis; only a part of the rod, rh., 

 with its constricted neck, is represented. Atgc. is a retinula partly trans- 

 formed into a ganglionic celi, but stili retaining some of its pigment. 



Piatesi. 

 «g. argentea. ce crystalline cone. 



ax.b. axial nerve bündle. bc^—bc- bacilli of pigment cells/^p'.i— 2. 



ax.f. » " fibre. b.m. basai membrane. 



