DEGENERATE EYES IN THE CUBAN CAVE SHRIMP. 273 



with a plasma stain as do some of the other tissues of the eye. 

 Does this consideration, together with the position of these clear 

 cells, afford us sufficient evidence to warrant us in regarding 

 them as degenerate cone cells ? I shall presently give a stronger 

 argument in support of this conclusion. What the dark masses 

 and the irregular patches of tissue represent I am not prepared 

 to say. I am not certain that they posses any special morpho- 

 logical significance. 



Beneath these structures is a group of larger cells with large, 

 deeply staining nuclei. The nucleus occupies nearly all the 

 space in the cell, there being only a narrow ring of cytoplasm 

 within the cell wall. A plainly marked fibrous tract, the optic 

 nerve, extends from these cells toward the optic ganglion. A 

 fine membrane separates this fiber and cell tract from the haemo- 

 lymph or spongy tissue on either side. The large cells are, 

 as I shall presently show, retinula cells. 



The Retina in the Right Eye. The tearing loose of the retina 

 from the cuticula has destroyed the cone cells and the hypoder- 

 mis at the tip so that no trace of either is visible. The looser 

 arrangement of the large, deeply staining cells permits of a more 

 accurate determination of their relation to the fibers of the optic 

 nerve. With the oil immersion lens, the fibers can be traced up 

 to these cells and can be seen ending in them. (Figs. 6, 7, n 

 and r/ 1 .) 



The objection may be urged that, since haemalum is not a 

 nerve stain, the fibers in question have not been shown to be 

 nerve fibers. The reaction to iron haematoxylin is not as marked 

 as in the fibers of the cephalic ganglion, but is still marked 

 enough to indicate that they are nerve fibers. The strongest 

 evidence that they are nerve fibers is their relation to the optic 

 ganglion and their correspondence in position and relation to the 

 nerve fibers in the normal eye. I believe that the simplest 

 explanation open to us is that the fibrous strand represents the 

 optic nerve. 



Parker ('95) states that, in the normal decapod (Astacus] eye, 

 the fibers of the optic nerve pass through the retinula cells and 

 disappear in the region of the rhabdome. There is no instance 

 known to me in which degeneration has caused a change in the 



