PLATE IV. 
Fie. 29. Outline sketch of sixth operative stage (XIII). > 614 diameters. 
Fig. 30. Section through eye region of an embryo of same stage (XIII) 
as above. The lens-vesicle is well divided off from the ectoderm, but still 
adherent to it. »X 45 diameters. 
Fig. 31. Experiment XIII,,. Section through right lens of an embryo 
killed 4 days after removal of the optic cup. The lens appears perfectly 
normal, but is not widely separated from the ectoderm. X 180 diameters. 
Fie. 32. Experiment XIII,,. Section through left normal lens of above 
4-day embryo. The lenses both measure the same, being about 140 w in 
diameter. X 180 diameters. 
Fie. 33. Experiment XIII,,. Section through right lens, 7 days after the 
complete extirpation of the optic cup. It measures only about 140 «in diam- 
eter, being about 30 ~ smaller than the normal lens. The medial pole is 
obliterated, and the entire lens is surrounded by a single layer of columnar 
epithelium. Xx 180 diameters. 
Fic. 34. Experiment XIII,. Section through right lens of an embryo 
killed 9 days after the complete extirpation of the optic cup. The lens 
measures about 150 in diameter, and is about 50. smaller than the normal 
left lens. The medial pole is quite obliterated, and the mass of lens-fibers 
within are beginning to degenerate. X 180 diameters. 
