SPINAL CORD REGENERATION. II 445 
in both directions which are ascending processes. As we have 
noted there is apparently an antagonism between these ‘like’ 
surfaces, demonstrated by the marked tendency on the part 
of the nerve fibers to avoid entering the opposite wound surface 
in those embryos with open wounds. In spite of this fact some 
of these fibers do enter the opposite cut surface and we may be 
very certain, in the case of those embryos in which per primum 
healing took place, that all of the fibers from the reversed middle 
piece grew in an abnormal direction. 
It is of course doubtful whether there is any real specificity 
of ascending and descending processes and the physiological 
result obtained certainly demonstrates that a considerable de- 
gree of adaptation has taken place here, in that the descending 
processes must certainly function as ascending processes and 
vice versa. In this sense therefore, we must conclude that 
there is a reversal in the polarity of the elements contained 
within the reversed piece of the spinal cord, though whether this 
reversal in polarity includes anatomical reversal of the cells 
themselves is very doubtful. It is much more probable that 
only the direction in which the stimuli travel along the processes 
is the reverse of its usual course. 
Not only do the nerve cells situated within the reversed piece 
of the spinal cord show a considerable degree of adaptability, but 
the piece as a whole adapts itself in a remarkable degree to its 
new environment. This is shown at the anterior wound surface 
in several embryos. Here we note that the canalis centralis of 
the reversed piece of the spinal cord (originally situated a milli- 
meter or more away from its present position) has become 
enlarged to form a rather typical funnel shaped outlet for the 
medulla, or the medullary ventricle has become contracted for 
the same purpose. In the first case, this has been accomplished 
by the thinning out of the dorsal portion of the spinal cord to 
such an extent that, in one or more cases, the point of union 
between the cord and the inferior medullary velum is indistin- 
guishable. In the latter case, the more usual one, the walls of 
the medullary ventricle have become thickened. 
