492 The Origin and Differentiation of the Lens 
The drawings were all made with the aid of a camera. 
Fic. 1. Outline of rana sylvatica at operating stage. The neural folds 
are partly, or in some embryos, completely fused. X 12 diameters. 
Fic. 2. Same embryo with large skin flap turned forward, exposing the 
brain with the optic vesicle, and the ganglionic masses of the cranial nerves. 
The ganglion of the fifth nerve partly covers the optic vesicle and was often 
partially removed. The skin flap is larger than the one usually used in the 
operations, the caudal edge of the operating flap being between the ganglia 
of the fifth and eighth nerves. X 12 diameters. 
Fic. 3. Section through optic vesicle region of rana sylvatica at operating 
stage. The fusion of the neural folds in this region is not complete. The 
ectoderm as yet shows no signs of lens formation. x 90 diameters. 
Fic. 3a. Outline of section through optic vesicles of rana sylvatica at 
operating stage. cd, position of cut for extirpation of the optic vesicle. 
xX 22 diameters. 
Fic. 4. Experiment DL,,. Embryo rana sylvatica killed 3 days after 
complete extirpation of the right optic vesicle. Transverse section through 
the right eye region. No traces of right eye or lens are to be found in the 
sections. Xx 90 diameters. 
Fie. 5. Section through left normal eye and lens of above embryo (experi- 
ment DL,,). X 90 diameters. 
Fic. 6. Experiment DL.,. Embryo rana sylvatica killed 5 days after the 
operation. Transverse section through the center of the left eye, right eye 
entirely wanting, except for a bit of the optic stalk (e). There is no trace 
of lens formation on the right side of the head. X 45 diameters. 
