434 DAVENPORT HOOKER 
over process has been less abrupt and a larger, more fusiform 
cavity results (figs. 7, 8). 
In one case, a piece of the notochord which was cut at opera- 
tion became interposed between the caudal wound surfaces 
(fig. 9). Healing was per primum and the end of the noto- 
chordal fragment became covered over by ependymal cells, thus 
projecting into the canalis centralis. As the fragment was in 
continuity with the rest of the notochord, the ventral fiber tracts 
were shifted laterally and upward to avoid the obstacle. Func- 
tion, in spite of the abnormal distribution of the fibers, became 
perfectly normal. 
Where the fusion of the cephalic wound has been complete, 
the canalis centralis of the originally caudal end of the reversed 
piece of the cord, now fused with the caudal end of the medulla, 
has undergone enlargement in a few cases. As a consequence, 
the medullary ventricle passes over into the canalis centralis of 
the spinal cord by a gradually tapering funnel. This is the 
normal condition of course, but in these operated embryos the 
wall of the funnel is formed in part from the ependymal cells of a 
portion of the canalis centralis normally situated a millimeter or 
more away. The point of fusion is noticeable in many of the 
specimens as a more or less pronounced notch in the ventricular 
wall, though in others the fusion is so perfect as to make it 
impossible to detect the line of healing. In other cases, however, 
it seems that the caudal extremity of the medullary ventricle 
has undergone a narrowing to produce this funnel (fig. 4), and 
that the canalis centralis of the reversed piece of the spinal 
cord has been unaltered in the process. In those cases where 
fusion or healing did not occur at the cephalic cut, the caudal 
end of the medulla is rounded over and closed. In some of these 
cases the ventricle is much enlarged. 
Effect of reversal of position upon the polarity of the cord. In 
the operative procedure described above, a piece of the spinal 
cord has been removed from its normal position, turned end-for- 
end and been grafted into the space from which it was removed. 
Its position was therefore reversed. The evidence given demon- 
strates that the neurones contained within that reversed piece 
