166 Charles W. Hargitt 
tic sense, the specimen responding subsequently almost as readily 
and sharply asothers. ‘This was particularly the case where some 
pains were taken to apply the two stimuli successively for a few 
times. Something akin to this was found in the earlier experi- 
ments where attempts were made to excise the gills (p. 304). 
Individuality 
In this class of experiments there was evident the same marked 
individuality of behavior as has already been shown in previous 
sections. For example, a given specimen, X, was found to be 
unusually indifferent to slight tactile stimuli. At one time its gills 
were gently stroked 123 times, some of the latter ones quite vigorous, 
before it finally retracted within its tube. “The same specimen at 
a later hour the same day was tested again. At the first touch 
it responded with a sharp and decisive retraction. After pro- 
truding it was again touched with a glass rod, and at the second 
test again retracted. ‘The third time it retracted after the fifth 
test. The fourth time only after the twelfth. The fifth time it only 
responded after the 115th stroke of the rod. On the sixth test it 
responded after the thirty-seventh stroke; and in the seventh test 
only retracted after the gills had been stroked 237 times, some of 
which were decidedly vigorous, and even then the reaction was 
not sharp or violent as in some cases. 
An interesting feature was observed during the progress of these 
experiments, namely, the exhibition of what seemed to be a defi- 
nite sense of tactile discrimination. While observing a group of 
specimens it was noticed that those occupying adjacent tubes often 
in the act of protrusion thrust their gills against one already ex- 
panded, but without in any way causing a retractile response on 
the part of either specimen. It was also observed that a specimen 
of Sabella living among the same colony occasionally thrust its 
body out of the tube for considerable distance and swayed it 
laterally and variously, jostling the gills of Hydroides in the pro- 
cess, but with the same negative results as have been referred to in 
the previous case. ‘To make the test still more explicit a specimen 
of Sabella was removed from its tube and, being held with forceps 
was used as a tactile brush, the gills of other species were brushed 
