Warren Harmon Lewis 463 
In experiment DL,, (Fig. +) there is another such piece of brain 
tissue connected with the transplanted eye, and between this piece of 
transplanted brain tissue and the irregular medulla is a large, strange 
nerve in a strange path. Its origin is certainly most satisfactorily ex- 
plained by the outgrowth theory. 
In another experiment (t;) a small piece of the ectoderm from the 
region, destined to form medullar plate in a gastrula of rana palustris, 
was transplanted into the region ventral to the otic vesicle of another 
and older embryo of rana palustris. This piece of transplanted ecto- 
derm has differentiated into nervous tissue and has sent out a long, large 
nerve, which passes through the mesenchyme into the region between 
the roof of the pharynx and the base of the cranial cartilage, where 
it ends abruptly in the mesenchyme (Fig. 5). This experiment illus- 
trates at once the great power of self-differentiation various portions 
of the central nervous system possess, even when they are isolated at 
such very early stages. It is impossible to determine whether this 
nerve is an extra one or represents a nerve, which, if the piece of central 
nervous system had remained in its normal position, would have arisen 
from it and taken a normal course as a cranial or spinal nerve. It 
occupies a path which is in no sense predetermined and can only be 
explained by its having grown out from this piece of transplanted 
tissue probably along the path of least resistance or in a direction accord- 
ing to the orientations of the nerve cells from which it arose. 
In experiment t, (Figs. 6 and 7) a piece of tissue just anterior to 
the dorsal lip of the blastopore of an embryo of rana palustris younger 
than that used in the preceding experiment was transplanted into an 
older embryo of rana palustris, whose neural folds had just closed. 
The piece of tissue hes in intimate contact with the dorsal wall of the 
pharynx in the region ventral to the otic capsule. It has differentiated 
into nervous system, and from it arises a nerve which runs in among 
the epithelial cells of the pharynx wall, divides into several bundles 
and can be traced for about 100 micro mm. and then appears to end 
in among these cells. This nerve clearly occupies a path in no sense 
predetermined for any known nerve, and the utter inadequacy any 
such explanation of its origin as would be given by a supporter of the 
Hensen doctrine is almost self-evident. 
In another similar experiment (t,,) almost exactly the same con- 
ditions are to be found, where nerve fibers extend, from a piece of 
brain tissue in contact with the pharynx wall, into the wall itself among 
the epithelial cells. 
Figs. 8, 9, and 10 are from embryos where the brain anterior to 
