54 T. H. MORGAN. 



A section of the eye somewhat deeper — that is, more outwardly 

 — than the last is shown in Fig. 35. Along the middle line the 

 central elements are cut transversely, showing the size in cross- 

 section of the outer ends of these elements. On account of the 

 bending of the outer retinal cells around the surface of the eye, 

 they are cut now farther down than in Fig. 34, where their walls 

 are thinner. Other elements lying between the central and 

 superficial ones are cut somewhat obliquely, and the walls of 

 some of these are seen to thicken, and to join the bacilli as they 

 approach the middle line. In the lower part of the figure one 

 sees that the bacilli show a double structure, so that one-half of 

 the thickness belongs to one cell and the other half to the neigh- 

 boring one ; so that they are really double, but usually the sepa- 

 ration into two parts is not seen, owing to the close fusion 

 between the cells. This figure also shows the entrance of a part 

 of the optic nerve, disappearing in the pigment layer. 



Fig. 36 passes almost through the middle of the eye, but prob- 

 ably somewhat nearer to its inner half. The most interesting 

 structures shown in the figure are the small rounded stainable 

 bodies in the central elements. These lie in the outer ends of 

 the cells found in the middle of the section. Around these the 

 protoplasm seems absent or thinner, so that each has sometimes 

 a halo about it. In other cells they are not seen, although they 

 show a clear portion in the protoplasm, and probably the bodies 

 are cut at a different level. The interlacing of the cells them- 

 selves in the central part of the eye should be noticed. They are 

 longer from side to side, giving them in cross-section a lanceolate 

 shape. At the sides of the section lie many scattered nuclei. 

 Lastly, the nerve fiber is seen entering the eye along the middle 

 line. The sections following this one as we pass to the outer 

 part of the eye add little or nothing to what we have gained 

 from the previous figures, and did not seem worth drawing. 

 The vacuoles in the outer part of the inner layer are very con- 

 spicuous in some of these sections, and one also finds a few 

 nuclei almost, or quite, in the middle line, but at all times they 

 show a marked tendency to bilateral arrangement. 



Such is the gross anatomy of the eye as gathered from sections, 

 and a great many sections were made, prepared by many dif- 

 ferent methods, to obtain even this meagre information. As a 



