274 



FRANK H. PIKE. 



location of a nerve ending. I consider the deeply staining cells 

 to be degenerate retinula cells. The cone cells have lost their 

 distinctive characteristics much more than the retinula cells. 



Summary.- -The degenerate eye has a relatively shorter stalk 

 than the normal eye. The corneal cuticula is thinner than that 

 on the outer side of the eye-stalk. The optic ganglion appar- 



. rt 



n 



FIG. 6. Eye of blind shrimp. 2 mm. oil immersion objective, 4 projection 

 eye-piece, x I,ooo. ;-/, retinula cell in which a nerve fiber, n, may be seen to end. 



ently consists of a single mass of fibers and cells.. There is nor- 

 mally some space between the optic ganglion and the cuticula of 

 the eye-stalk. The optic nerve, extending from the optic gang- 

 lion to the retina, is present. The retinula cells, in which the 

 fibers of the optic nerve terminate, still persist. The vestiges of 

 the cone cells may be, and probably are, present. The structures 

 serving to distinguish light from darkness, probably being older 

 phylogenetically than the structures concerned with the produc- 

 tion of a definite image, are less degenerate than the latter. The 

 active structures of the eye, represented by the retinula cells, 

 have degenerated vastly more than the passive structures such as 

 the cuticula. 



