SPINAL CORD REGENERATION. II 437 
been caused by the pressure of the hair upon it, this type of 
response could be almost unfailingly obtained. The constant 
reappearance of this type of response lends further evidence in 
favor of the view that a single quick bending of the head toward 
the side stimulated is the most primitive reaction to tactile 
stimulation in the freg embryo. 
This type of response is quickly followed by a typical ‘avoiding’ 
reaction. This reaction makes its appearance within two to 
three hours after the beginning of sensitivity to tactile stimu- 
lation of the embryo and lasts for a varying period. 
Embryos from thirty-six to forty-eight hours after operation 
almost uniformly exhibit a double C reaction. The term 
‘double C’ reaction has been applied to that form of response 
in which the embryo on stimulation contracts into an are, 
straightens out and contracts into a similar are on the opposite 
side. This constitutes the complete reaction to a single stimula- 
tion. This is true even of those embryos which do not begin 
to exhibit any response until after the first thirty hours. These 
embryos which are late in beginning their reaction appear to 
hasten through the earlier stages so that they tend to become 
uniform in their response at this later period. It was noted 
that at the very beginning of this type of response there seemed 
to be a tendency on the part of many of the embryos to con- 
tract first on the side stimulated, but there is not sufficient 
evidence to prove that the first contraction toward the side 
stimulated is any more decidedly frequent in appearance than a 
first contraction away from the side stimulated. During the 
beginning of the appearance of this type of reaction the two 
contractions toward opposite sides of the body constituted the 
entire response, but within a very short time, frequently not 
more than half an hour afterwards, the embryos exhibited a 
series of these double C reactions to each stimulation. 
This type of reaction lasts for a relatively long time, from six 
to twelve hours, and it is followed by a typical S or sinuous re- 
action. During the latter part of the double C reaction period, 
at a time which apparently bears no relation to the beginning 
of the appearance of the § reaction, the embryos exhibit spon- 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, wo. 4 
