THE NERVE DISTRIBUTION IN THE EYE OF PECTEN IRRADIANS. 477 



anterior end of the retina, but also to the marginal ganglionic cells and upward along 

 the side toward the cornea. The most important distribution of their fibres is the 

 network formed of several fibres from each cell. These fibres meet near the cells 

 and then send out many very fine beaded branches that form an arborescent network 

 around the cells of the anterior, middle, and posterior layers to end on the bipolar cells 

 and rod-cells (Fig. 2). These fibres can be seen in well-stained methylen-blue sections 

 at a magnification of 2,500 diameters. They form, as seen in some sections, a fine 

 weblike tissue surrounding the outside of the rods (Fig. 1, Jbr. mot.). 



In addition to the four nerve elements thus briefly described, the retina possesses 

 a middle and an anterior layer of supporting cells that can best be studied from sec- 

 tions other than those impregnated with methylen-blue. The middle supporting 

 cells extend from the median limiting membrane between the bipolar cells, whose 

 curved courses they follow toward the periphery of the anterior limiting membrane, 

 and form thus a disk of a single layer of cells (Fig. 2, sst. m.). They too describe 

 curved .lines that grow more curved and shorter as they approach the periphery of 

 the retina. From their broad bases that abut against the median limiting membrane, 

 they gradually become more attenuated, curving under the anterior limiting mem- 

 brane to end at the margin of the retina. They are filled with granular protoplasm 

 and have large spherical nuclei near their thin peripheral ends. They are easily dis- 

 tinguished from the elliptical bipolar nuclei which lie nearer the median limiting 

 membrane. The anterior supporting cells (Figs. 1, 2, 3, sst. a.) form a single row 

 of pyramidal bodies that extend from the anterior limiting membrane to the septal 

 membrane. They are granular and possess large spherical basal nuclei. Among 

 the bases of these cells are occasionally seen what seems to be dark nuclei with refrac- 

 tive capsules. They may possibly be transverse sections of some of the bipolar cells. 



V. DISCUSSION OF RESULTS. 



In comparing the results of Hensen ('65), of Hilger ('85), and especially of Patten 

 ('86) with mine, it will be noticed that their descriptions and interpretations of the 

 nerve distribution in the eye of Pecten and consequently of the morphological ele- 

 ments, differ markedly from those advanced in this article. Patten classifies the 

 structural elements of the eye under two heads: First, a posterior wall consisting of 

 four layers, namely, an outer vitreous network, two layers of argentea, and a red 

 tapetum; second, an anterior wall of four layers as follows: rods containing the 

 retinidia, retinophorse, inner ganglionic cells, and outer ganglionic cells. In my 



