462 Evidence of the Outgrowth of the Axis Cylinder 
tinued their growth and differentiation in this strange location. From 
the small piece of brain there extend into the mesenchyme large num- 
bers of nerve fibers (Figs. 1 and 2). hese fibers extend in various 
directions into the mesenchyme without reaching end organs of any 
kind. For the most part the fibers are free from sheath cells. At 
first, of course, no protoplasmic bridges existed between the nerve cells in 
the transplanted brain, and any of the end organs of the host, and it is 
very difficult to imagine how they could have subsequently been formed. 
It is, of course, equally difficult to form a rational conception of how 
such bridges are subsequently transformed into nerves which take such 
an erratic course as those shown in Figs. 1 and 2. What possible end 
organs are there to account for this enormously greater number of 
nerves than are normally present in this region. Then again, these 
nerves are ones which, if the piece of brain had remained in its original 
position as a part of the brain, would, for the most part at least, have 
remained within the brain, and therefore the cells of the transplanted 
piece are ones which normally never connect in a direct way with 
peripheral end organs. I see no possibility of explaining these fibers 
by the Hensen doctrine. The absence of sheath cells makes it likewise 
impossible to explain their origin by the cell chain theory. It is evident 
also from this experiment that it is not necessary to have a predetermined 
path laid down before a nerve can grow out from its center towards 
the periphery. That there are such paths, and that they are necessary 
under normal conditions for the proper connection of the central nervous 
system with its end organs is in no way controverted by this experiment. 
In experiment (IV,) (Fig. 3) there is a somewhat similar piece of 
transplanted brain tissue connected with a transplanted optic vesicle of 
rana palustris. The section shows the differentiated piece of brain 
tissue ventral to the otic capsule and from it a large nerve has grown 
to the myotome. ‘The piece was transplanted from the eye region into 
the otic region of the same embryo, whose neural folds had just closed, 
and so long before the nerves were present, and this nerve, as in the 
preceding experiment, occupies a strange path in the mesenchyme, and 
its presence can scarcely be explained in any other manner than as an 
outgrowth from the piece of transplanted brain. Whether the myotome 
has acted as a chemotactic agent or not can scarcely be determined from 
this one experiment alone, as it might be that the nerve has merely 
followed the path of least resistance which happened to be towards the 
myotome. Nor am I able to determine as to whether the nerve ends 
bear the same functional and anatomical relation to the muscle fibers 
that a normal motor nerve would. 
