438 ALFRED O. GROSS 
animals with theii' palps removed is increased to 21.57 seconds 
with a probable error of 1.45. Substituting the values in the 
formula as above stated, we have 
21.57 - 9.44 12.13 ^ 
V(.479)2+ (1.45)2 1.52 
A significance factor greater than about 3 signifies the results 
are to be considered of scientific value. No importance is to 
be attached to the difference in reaction times if the signifi- 
cance factor falls below 3. Furthermore, if this factor becomes 
greater than 3 in the two sets of readings of the control, 
then the results of the experiments become questionable, either 
because of lack of care in performing them or because certain 
factors, such as hght, temperature, etc., were not properly kept 
under control. An examination of the tables at once reveals 
the fact that the palps and tentacles are so highly sensitive to 
chemical stimulation that their removal causes a marked change 
in the reaction times of the animals. The tentacular cirri, which 
together have a much greater exposed surface than the ten- 
tacles and palps combined, are sensitive to a much less degree; 
indeed, in only the HCl test was there a noticeable change in the 
reaction time when the eight tentacular cirri were removed. 
The significance factor in this case is only 4, so even here the 
difference in reaction time becomes of doubtful value. The 
anal cirri, though they are sensitive to chemical stimulation, 
are not sensitive to the degree that their removal causes a meas- 
urable change in the responsiveness of the worms. 
DISCUSSION 
The fact that the palps and tentacles are much more sensitive 
to chemical stimulation than the tentacular cirri becomes of 
more interest when the innervation of these appendages is con- 
sidered. The palps and tentacles are supplied with well-devel- 
oped nerves, which arise directly from the supra-oesophageal 
ganglion or brain, whereas the two pairs of tentacular cirri are 
innervated by nerves which have a very different origin. The 
