DEVELOPMENT OF THE EYE OF AMBLYOPSIS. 



155 



nuclear layers. The relative development of the pigment layer and the inner 

 reticular layer both show a less degree of differentiation than the same layers 

 in the eyes of another series of larvae only 6 mm. long. This is due to the 

 individual variation in the rate of development, not to degeneration since the 

 last stage. 



Dividing cells are found in the nucleated layer. In the nuclear layers some 

 nuclei elongated in a vertical direction are probably the nuclei of the Miillerian 

 fibers. 



FIG. 63. (a) Horizontal Section 10 /x Dorsal to that given in fig. 60 f, and showing Iris and Vitreous Cavity. 



(6) Outline of Lens of Same Eye as that shown in Jigs. 60 e and 61 a but at a Level Dorsal of tig. 61 a, 



(c) Region between Eye and Epidermis of Larva 7.5 mm. long, showing Degenerating Lens. 



(rf) Lens of Larva about 7 mm. long. 



(el Vertical Section near Center of Right Eye of Fish 9.5 mm. long. 



(/) Anterior Face of Transverse Section through Eye of Fish 9.5 mm. long. 



(g) Horizontal Section through Left Eye of Fish 0.5 mm. long. 



NINE TO TEN-MILLIMETER STAGES. 



In larvae 9 to 10 mm. long the eyes lie from 60 to 100 ^ removed from the epi- 

 dermis and in contact with the brain capsule or but little separated from it. Their 

 average measurements are: longitudinal diameter, 114 /LI; antero-posterior, 98 /^ ; 

 vertical, 106 /x (figs. 63 c, 64 b). 



The epidermis over the eye has assumed the thickness found over neighboring 

 regions, and from now on till death by old age there are no external modifications 

 to indicate the former position of the cornea. 



The pupil is still open, and also the choroid fissure in the region of the pupil 

 (figs. 63 e, g). In the proximal portions the choroid fissure is indicated by the 

 absence of pigment along the ventral line (fig. 63 /). The vitreous cavity is a 



