M. M. METCALF ON THE EYES AND SUBNEURAL GLAND OF SALPA. 315 



The eye is innervated by two optic nerves that arise in the non-cellu- 

 lar core of the ganglion (Plate XLIX, Figs. 1, 4 and 6, on). The fibers run 

 in two bundles, one on each side, over the posterior and dorsal faces of the 

 two posterior limbs of the eye, some of them here entering the clear 

 ends of the rod cells. Further forward, at the point where the relative 

 position of rod cells and pigment cells is reversed, the fibers on each side 

 divide into two bundles ; one bundle going directly to the clear ends of 

 the rod cells of the second, smaller portion of the eye (Fig. 2) ; the other 

 passing around the inner side of the eye, below the secondary portion, to 

 innervate in the same way the rod cells of the anterior portion of the eye 

 (Plate XLVIII, Fig. 9, on"). The origin of the two optic nerves is shown 

 in Fig. 4, Plate XLIX, which represents a cross-section of the ganglion, 

 through the region designated by on in Fig. 1. Fig. 6 is an enlarged 

 drawing of the section of the left limb of the eye shown in Fig. 5. In 

 this figure the optic nerve, on, appears on the dorsal surface ; ventral to 

 this are the rod cells with their clear ends, s, containing large nuclei, 

 and their thick-walled, deeply staining ends, r; ventral to these and 

 abutting directly upon them is the layer of crowded pigment cells, p, 

 so full of pigment granules that no structure can be made out. Over 

 the whole surface of the retina the delicate membrane, z, is seen. 



In one case the dorsal eye was removed from a hardened specimen 

 of the chain Cyclosalpa pinnata and, after maceration in Haller's fluid, 

 was gently torn with teasing needles. A bit of the smaller portion of 

 the eye, e'", was in this way isolated with some of its nerve fibers still 

 attached. Fig. 7, Plate XLIX, which represents an optical section of this 

 piece, shows very clearly the separate fibers connecting with single rod 

 cells. This was even more clearly shown in more finely teased portions. 

 The innervation of the eye is well shown in Figs. 7 to 9, Plate XLVIII, 

 which represent sections of the nearly mature eye of one of the older 

 individuals attached to the stolon of the solitary salpa. 



In Fig. 3, Plate XLIX, is seen a section of a portion of this eye 

 cutting the thick-walled ends of the rod cells at right angles to their 

 long axis. The walls of adjacent cells are so closely pressed together 

 that they seem to form a single continuous network. In my unsuc- 

 cessful macerations of the hardened eyes I could see in several cases a 

 slight separation of the rods of adjacent cells, but the preparations 

 were not sufficiently satisfactory to draw. (See Fig. 7, Plate XLIX, 

 which shows imperfectly the same thing.) The appearance indicated 

 that this seeming network is not a continuous structure, but rather 



