276 The Origin and Differentiation of the Optic Vesicle 
Fic. 24. Experiment DL,,;. Embryo killed 5 days after cutting off and 
transplanting the right optic vesicle. Section through ventral portion of 
brain showing symmetrical position of two optic stalks. The left one (right 
in figure) entends to the normal eye, the other one extends but a short dis- 
tance and ends abruptly. The tranplanted eye is large and has a bit of trans- 
planted brain attached to it. Xx 100 diameters. 
Fic. 25. Experiment DF,,. Embryo killed 4 days after the operation. 
Section through ventral part of brain and optic stalk. The normal left one 
reaches to the eye. The right one ends in a slight enlargement but has no 
pigment or retinal layer cells. The transplanted eye is large and there is 
no transplanted brain tissue. X 100 diameters. : 
Fic. 26. Experiment dya,. Embryo killed 9 days after cutting off the 
optic vesicle. Section through very small regenerated eye which has all the 
layers of the retina somewhat irregularily arranged. X 100 diameters. 
Fic. 27. Experiment IV,,. Embryo killed 5 days after cutting off the 
optic vesicle. There is a very small deeply situated regenerated eye with 
retinal and pigment layers, the differentiation of the retina is much retarded. 
The eye is connected with the brain by a large optic stalk. X 100 diameters. 
Fic. 28. Experiment DO,. Optic vesicle of rana sylvatica at stage of 
fusion of medullary fold transplanted anterior to otic vesicle of amblystoma 
at stage when the lens-plate is quite thick. Embryo of amblystoma killed 
5 days after the operation. Section through transplanted eye and lens and 
part of medulla showing large regular invagination of optic cup with forma- 
tion of layers of the retina. X 90 diameters. 
Fie. 29. Experiment DO,. Operation as in Fig. 28. Embryo of amblys- 
toma killed 5 days after the operation. Section through transplanted eye and 
lens and part of medulla showing differentiation of eye and lens. xX 90 
diameters. 
Fic. 30. Experiment DF,,. Embryo rana palustris killed 4 days after 
transplantation of the optic vesicle into the region between medulla and 
otic vesicle. Section showing the relation of the optic nerve to the outer layer. 
The transplanted eye is without a lens but shows about the same 
degree of differentiation as the normal eye, the invagination cavity is 
shallow and the pupil wide. The optic nerve leaves the retina by the cleft 
region and passes into the outer layer. It runs in among the pigment cells 
of the outer layer as a distinct bundle for about 1% the circumference of the 
eye. The nerve does not leave the outer layer, but remains as a compact 
bundle of fibers. : 
Fic. 31. Experiment DF,. Embryo rana palustris killed 5 days after 
transplantation of the optic vesicle into the preotic region. Section through 
transplanted eye showing somewhat irregular invagination and the optic 
nerve. The latter has been projected in part into the figure from the neigh- 
boring sections. The optic nerve soon after its origin splits into two parts, 
the larger division runs through the retina to the outer layer but does not 
penetrate into it, its fibers ending among the rods and cones which are just 
developing. The smaller division enters the outer layer, runs for a short 
distance within it, then splits the smaller division ends in among the cells of 
the outer layer after running through a few sections. The larger division 
soon leaves the outer layer and runs for some distance in the mesenchyme 
and seems to join the third cranial nerve. There is no indication of a chor- 
oidal fissure in the transplanted eye. » 90 diameters. 
Fic. 32. Experiment DF,.,. Optic vesicle transplanted caudal to the otic 
vesicle, its nerve passes into the medulla and can be traced anteriorly for 
many sections as a distinct bundle. Section through this bundle 0. X 90 
diameters. 
