470 Evidence of the Outgrowth of the Axis Cylinder 
Fic. 14. Experiment DF;. Embryo rana palustris killed 4 days after 
transplantation of optic vesicle into position caudal to normal eye region. 
Section through transplanted eye showing formation of optic cup and course 
of optic nerve from transplanted eye into medulla in the region of the V 
nerve. The optic nerve passes through the marginal veil into the grey matter 
where the fibers become scattered and can only be followed for a few sec- 
tions anteriorly. The transplanted eye is separated from the ectoderm by 
mesenchyme and is without a lens. It is in contact with the medulla. 
x 90 diameters. 
Fic. 15. Experiment DF,,. Embryo of rana palustris killed 5 days after 
transplantation of the optic vesicle into the region caudo-central to the otic 
capsule. Section through anterior end of transplanted eye showing position 
of optic nerve-fibers. The optic nerve is projected into this section in part 
from the adjoining section. x 90 diameters. 
Fic. 16. Experiment DF,,. Section 30 micro mm. caudal to one in figure, 
showing optic nerve-fibers leaving retina and running among the cells of the 
outer layer. X 360 diameters. 
Fic. 17. Experiment DF,,. Section 50 micro mm. caudal to above, show- 
ing optic nerve-fibers close against the outer layer. > 360 diameters. 
Fic. 18. Experiment DF,,. Section 30 micro mm. caudal to above, show- 
ing similar position of optic nerve. X 360 diameters. 
Fic. 19. Experiment DF,,. Section 40 micro mm. caudal to above, show- 
ing optic nerve running from outer layer into medulla caudal to otic vesicle. 
The optic nerve-bundle can only be followed a few sections in the medulla. 
x 360 diameters. 
Fic. 20. Experiment DF,,,. -Embryo rana palustris killed 19 days after 
transplantation of the optic vesicle into the region between the eye and the 
otic vesicle. Section through middle of transplanted eye and side of brain. 
The transplanted eye shows invagination and differentiation of the layers of 
the retina, the cup cavity and pupil are much smaller than normal, and 
there is no trace of a lens. The ganglionic layer bordering the cavity has in 
places only a few scattered cells as most of the cells form a heap projecting 
into the cavity and from this heap of cells a nerve arises which passes across 
the cavity through the narrow pupil out into the mesenchyme to the sub- 
ectodermal pigment band. There is also a small optic nerve passing through 
the retina into the outer layer, the figure shows its position here as pro- 
jected from the two neighboring sections. It can be traced for a short 
distance only in the outer layer. X 90 diameters. 
Fic. 21. Experiment DF,,;. Embryo rana palustris killed 18 days after 
transplantation of the optic vesicle into the region between the otic capsule 
and medulla. Section through transplanted eye, otic capsule, and medulla. 
The eye, owing to irregular invagination, has only a very narrow pupil and 
small, irregular cup cavity. Most of the optic nerve-fibers pass from the 
irregular ganglionic layer through the narrow pupil into the mesenchyme 
ventral to the otic capsule, where it splits into two divisions, the ventral 
one of these runs a short distance and ends abruptly in the mesenchyme, 
the other runs to the cartilage ventral to the otic vesicle and can be traced 
for a short distance along it. The peripheral portion of the nerve, as shown 
in the figure, is projected into the section from the neighboring sections. 
Another portion of the optic nerve, smaller than the first one, runs through 
the retina and seems to end abruptly at the pigment layer. This portion of 
the nerve has also been projected into the figure from a neighboring sec- 
tion. > 90 diameters. 
