468 Evidence of the Outgrowth of the Axis Cylinder 
Fic. 6. Experiment t,. Embryo rana palustris killed 12 days after having 
had a small piece of the ectoderm anterior to the dorsal lip of blastopore of 
an embryo of the same species transplanted into the otic region. The 
embryo at the time the piece was transplanted into it had completed the 
closure of the neural folds. An examination of the sections show that the 
transplanted piece has differentiated into nervous tissue like that of the 
central nervous system. The figure is from a section through this trans- 
planted piece and shows its location ventral to the otic vesicle and in inti- 
mate contact with the dorsal wall of the pharynx. From this piece of brain 
tissue nerve-fibers pass into the epithelial wall of the pharynx and can 
then be traced in among the cells for about 100 u. XX 90 diameters. 
Fie. 7. Experiment t,. Section through pharynx wall showing position 
of nerve-fibers between the epithelial cells. » 360 diameters. 
Fig. 8. Experiment DL,,. Embryo rana sylvatica killed 5 days after 
partial extirpation of the right optic vesicle. The brain anterior to the 
attachment of the optic stalk was injured. Section through injured region 
showing extra nerve which runs out into mesenchyme, it divides part, forms 
a loop, and enters the brain again dorsal to its origin; the main branch 
turns abruptly caudalwards and can be traced through many sections until 
it appears to join a portion of the Gasserian ganglion. A few sections caudal 
to the origin of this nerve another extra nerve arises from a similar position 
on the brain; it can only be traced a few sections out into the mesenchyme. 
The nerve shown in the figure from a composite of the 3 or 4 neighboring 
sections. X 90 diameters. 
Fic. 9. Experiment DL,,. Embryo rana sylvatica killed 5 days after 
partial extirpation of the right eye. Section through anterior end of regen- 
erated right eye and brain showing a small extra nerve running from the 
brain to a small ganglionic mass. This section is 80 ~ anterior to the optic 
nerve, and on the normal side there is no trace of such a nerve between the 
olfactory and optic nerves. X 90 diameters. 
Fic. 10. Experiment DL. Embryo rana sylvatica killed 3 days after 
partial extirpation of the right eye. Section through fore-brain 100 ~ anterior 
to optic nerve showing large extra nerve leaving brain and running out into 
mesenchyme. This nerve splits into several branches, the longest and largest 
runs caudally over the dorsal surface of the regenerated eye and is lost in 
the mesenchyme caudal to the eye. There is no corresponding nerve on the 
normal side. The brain on the right side is irregular and evidently was 
injured during the operation. X 90 diameters. 
Fic. 11. Experiment bx,. Embryo of amblystoma killed 9 days after 
removal of anterior portion of brain. The brain was removed through a 
dorsal incision before the first appearance of the cranial nerves. Section 
through anterior end of head showing anterior ends of eyes and nasal pits 
with nerve-fibers passing out into the mesenchyme from the latter. The 
ectoderm in the mid dorsal region dips down into the mesenchyme in the 
region from which the brain was removed. X 45 diameters. 
Fig. 12. Experiment Sp,. Embryo of amblystoma killed 16 days after 
having had the nasal pit of another embryo transplanted beneath the ecto- 
derm in the region dorsal to the right eye. Section through right eye and 
transplanted nasal pit. Where the nasal pit is in contact with the outer 
layer of the optic cup this portion of the outer layer is free from pigment 
and in places of greater thickness than normal. Between the nasal pit and 
ectoderm are olfactory nerve-fibers. %* 45 diameters. 
Fic. 13. Experiment Sp,. Section through edge of nasal pit and ecto- 
derm showing the position of the olfactory nerve-fibers. Sections anterior 
to this one show olfactory nerve-fibers passing from the nasal pit a short 
distance ventrally close to the median surface of the eye. X 180 diameters. 
