602 William Patten 



itely in the retinal layer, tliey now appear to end abruptly in the drawn- 

 out ends of the ganglionic cells. Besides the nerves , the fibrous layer 

 also contains numerous, minute and deeply staiued particles, which, in 

 the later stages, disappear entirely (fìg-. 17 n. f.). The middle, or 

 ganglionic layer is formed of a single row of large. round nuclei, whose 

 cells are filled with coarse, granular protoplasm. The periphery of the 

 retina is filled with several rows of nuclei , imbedded in a clear proto- 

 plasm, a part of which gradually grows toward the centre of the eye, 

 and forms a clear, narrow band beneath the ganglionic layer (fig. 17). 



The lens has increased somewhat in size (compare figs. 5 and 17) 

 and begins to show traces of its future shape ; at its periphery, it stili 

 passes insensibly into the thin layer of connective tissue cells, surround- 

 ing the optic vesicle. 



The epithelium of the eye consists of a thin layer of cells, the 

 nuclei of which are widely separated. The greenish yellow pigment 

 granules , which at first were only present around the base of the eye, 

 bave encroached upon the anterior pole, around which they form a deeply 

 pigmented and nearly complete ring, the iris. The anterior pole re- 

 mains colorless and forms the cornea. The iris is best developed upon 

 the branchial side of the eye ; on the opposite side only traces of pig- 

 ment are to be found. 



The tape tum forms a single layer, filled with red pigment, be- 

 fore the pigment of the iris has appeared. The cells first become 

 filled with coarse, colorless and refractive granules, which 

 soon acquire the characteristic red color of the tapetum. 



The nuclei of the retinophorae, which at first form a thickened 

 ring around the retina, gradually grow inwards towards the centre of 

 the eye. It is not tili quite late in the development, after the appearance 

 of the rods, that the celi walls, containing the nuclei, become visible. 



To determine the exact manner in which the rods develope, is an 

 extremely difficult problem. Although my sections of that stage were 

 most numerous and perfect , I was unable to come to any satisfactory 

 conclusion as regards their origin. The clear space , represented in 

 fig. 17, y, increased in thickness up to a certaiu point and then the faint 

 outlines of the rods, togetherwith the pseudo-membrane, suddenly 

 appeared, only a little less distinctly than those of fig. 10. The only 

 difference, between the rods wheu first seen and those of the adult, was 

 in the large size of the axial core of the former, and the extremely 

 thin shell , or sheath , scarcely visible except at the tips of the rods. 



