160 Charles W. Hargitt 
two tests. This interval was, on the average, about five minutes, 
sometimes less, or slightly more, as conditions might require. 
Of the signs employed in the tables, namely, plus, minus, and zero, 
the first two indicate simply positive and negative reactions of the 
specimens, i. e€., retraction into the tube or failure to retract. 
That of zero signifies that in a given test the specimen so designated 
was out of commission or, in other words, had withdrawn into its 
tube at the time the test was made. ‘This was not frequent, but 
as will be seen it happened occasionally with different specimens. 
The letters A, B, C, etc., arbitrarily indicate the record of given 
specimens throughout the series of experiments of a given table. 
The numbers at the left of the tables indicate the number of the 
tests of a given day or time. 
As a check against possible error which might be involved in a 
too rigid attention to results obtained from laboratory experi- 
ments some pains were taken to observe the behavior of specimens 
in their natural habitat. This was possible by selecting speci- 
mens to be found along the lower tide lines and in tide pools, and 
at favorable times when the surface was smooth on still days, thus 
making observation ‘practicable, tests were applied similar to 
those employed in the laboratory. Without taking time for ex- 
tended details it may suffice to state that the reactions obtained 
from shadow and tactile stimuli were essentially the same as the 
former, and confirmed them in almost every particular. Some 
differences as to individual reactions were perceptible, especially 
as to tactile responses. ‘This | am disposed to attribute to the 
peculiarity of the habitat. It seems not unlikely that the effects 
of the buffeting of wave action to which these specimens are more 
or less subject may account for these apparent differences 1n tac- 
tile reaction. 
Another feature was apparently quite different in the shore speci- 
mens, namely, the close adherence of the tubes to the substratum 
on which they grew. There was no tendency to growupright 
and free, as was the case in those from deep waters. And this 
again may be interpreted as a further expression of the conditions 
involved in the environment. It would be quite impossible for 
the tubes to withstand any such buffetings as the waves and pound- 
