466 Evidence of the Outgrowth of the Axis Cylinder 
Fic. 1. Experiment Pe,. Embryo amblystoma killed 21 days after opera- 
tion. The optic vesicle and piece of brain tissue adjoining it were trans- 
planted from an amblystoma embryo, of a stage shortly after fusion of the 
neural folds, before the nerves appear, into the region between the otic 
vesicle and medulla of an older embryo. Section through transplanted eye 
and brain showing large groups of nerve-fibers running out into the mesen- 
chyme in various directions; most of them are without sheath cells. Portions 
of these fibers from the neighboring sections were projected into the figure. 
x 90 diameters. 
Fic. 2. Experiment Pe, Section through another portion of this trans- 
planted brain showing other groups of nerve-fibers leaving it. These various 
nerve-fibers have been projected into the figure from the neighboring sections. 
They do not include those in Fig. 1. X 90 diameters. 
Fic. 3. Experiment IV,. Embryo rana palustris killed 5 days after trans- 
plantation of right optic vesicle and part of adjoining brain wall to the 
region ventral and posterior to the otic capsule. Section through portion of 
transplanted brain, posterior end of otic vesicle and medulla. From the 
transplanted brain a large nerve passes directly through the mesenchyme to 
the myotome. The distal 144 of the nerve is projected into the figure from 
the adjoining sections. xX 90 diameters. 
Fic. 4. Experiment DL,,. Embryo rana sylvatica killed 5 days after trans- 
plantation of optic vesicle caudal to otic capsule. The ectoderm and medulla 
were injured during the operation in the region into which the eye was trans- 
planted. Section through this injured region caudal to otic capsule and 
anterior to transplanted eye. There is an increase in the size of the irregular 
medulla at the place of injury, and from here a large extra nerve passes to 
the ganglionic mass connected with the injured place on the ectoderm. Ven- 
tral to this extra nerve is seen a portion of the 10th cranial nerve which 
joins the medulla here. x 90 diameters. 
Fig. 5. Experiment t;. Embryo rana palustris killed 12 days after having 
had a small piece of the medullary plate region from the gastrula of another 
rana palustris embryo, transplanted into the region ventral to the otic cap- 
sule. Section through this transplanted piece which has developed into brain 
tissue and sent off a long nerve which passes medianwards between the base 
of the cranial cartilage and the roof of the pharynx. This nerve ends in the 
mesenchyme. The ventral part of the otic vesicle is seen in the section 
x 90 diameters. 
