432 DAVENPORT HOOKER 
opposite wound surface chiefly on the part of the sensory fibers 
which causes the failure of so many of the embryos with primarily 
unfused wounds to re-establish continuity of the cord and, in- 
deed, to live. This apparent antagonism between ‘like’ wound 
surfaces has been noted by many investigators who have worked 
on the reversal of the position (and polarity) of parts of organ- 
isms. That it exists in those embryos in which the wounds are 
caused to heal per primum by close approximation of the cuts 
is without doubt, but the very fact of fusion prevents its ex- 
pression in so marked a manner as is permitted by the separation 
of the cord ends in the embryos under discussion. The fact that 
in a very few cases the late stages of complete reunion have been 
obtained in these embryos, does not militate against the effective- 
ness of the antagonism as a factor which oppose such re-establish- 
ment of the continuity of the cord, as, in all these embryos, the 
healing is not as clean cut as in those with unreversed cords. 
In those embryos in which complete healing is being effected 
the same stages as those found in the re-establishment of con- 
tinuity after simple severing (outgrowth of ependymal fibers, 
wandering out of cells into the fiber mass and elongation of the 
canalis centralis) are to be found, though in somewhat more 
fragmentary form in the majority of cases. A very few embryos 
show complete healing and these differ in no essential respect 
from the final stages observed after a single severing out of the 
cord beyond the presence of a number of irregularly situated 
nerve fibers which run out from the cord into the surrounding 
mesenchyme to end there, apparently blindly. 
The reversed middle piece. Whether the reversed piece has 
fused with the normal cord and medulla at operation, has healed 
at one or both ends by the active regenerative processes indicated 
above or has failed to establish union at. either end, it stull 
possesses certain characteristics which make it readily identifi- 
able. The cephalic cut, it will be remembered, passed through 
the caudal end of the medulla, leaving a part of the cavity with 
the piece to be reversed. This cephalic end, now directed cau- 
dad, shows the fragment of medullary ventricle as a small, usu- 
ally almost spherical cavity (figs. 4, 5, 6) in all but two cases. 
