446 DAVENPORT HOOKER 
A more extreme example of the capability for adaptation on 
the part of the spinal cord is demonstrated in another embryo 
(fig. 9) in which a portion of the notochord became inserted be- 
tween the posterior wound edges at operation. In this case, 
we have a resulting fistula into the canalis centralis occupied 
by the end of the piece of notochord, but the embryo appar- 
ently suffered no ill effects from the consequent diversion of the 
nerve tracts from their normal course. In fact, this embryo 
was one of the best in point of executing the various movements 
and was only distinguishable from normals by the spur of the 
dorsal fin. In spite of the large cavity in the ventral surface of 
the spinal cord, the connections between the original caudal end 
of the reversed piece and the medulla were apparently completely 
re-established. This necessitates, of course, an increase in the 
number of fibers which pass laterally along the side of the cord 
and which must have bridged an open gap to re-establish the 
continuity. 
The results of the observations on the nature of the primary 
responses in these embryos with a reversed middle piece demon- 
strates certain very important facts in regard to their origin. It 
is to be noted that each portion of the embryo goes through a 
graded series of responses to tactile stimulation which is as 
follows: (1), contraction of the myotomes on the same side as 
that stimulated, giving a bending of the body toward the side 
stimulated; (2), a contraction of the myotomes on the opposite 
side from that which receives the stimulation, giving an avoiding 
reaction; (3), an alternate contraction of the myotomes on oppo- 
site sides of the body, giving a double C reaction; (4), a primi- 
tive swimming movement. Furthermore it is to be noted that 
the middle segment of the body, which has been reversed in 
these experiments is the region which actually determines the 
locomotion of the animal as a whole and it is in this region that 
this succession of responses to tactile stimulation is best to be 
observed. In the head region we note that the reaction toward 
the side stimulated and the avoiding reaction are of the same 
nature as in the other parts of the body. The double C reac- 
tion consists of a side-to-side swaying of the head, for owing to 
