180 Charles W. Hargitt 
part of the largely negative results found in specimens from 
deep waters, already referred to in an earlier connection, the dim 
light of the basement having operated as the similar dim light of 
the depths. 
Second, the possibility that long-continued association of the 
presence of passing shadows unaccompanied by harm had in- 
duced a state of indifference to such stimuli, a not unsupported 
view of the case. Or, third, the possibility that long existence in 
the aquarium had acted to lessen the sensory activity, due in part 
perhaps to a lowered state of general vigor. Both my former dis- 
cussion of this point, and the somewhat anomalous results ob- 
tained by Yerkes in certain cases, would seem to support the last 
alternative. 
Whether one, or something of all these factors may share in the . 
real explanation it would be of small consequence to discuss from 
so limited a body of facts. Some further hints may be afforded in 
the later accounts of these specimens. ‘The colony was kept in 
the strong light on my laboratory table and tested daily for some 
two weeks, both by shadow and tactile stimuli. As a result of 
these it soon became apparent that a marked improvement was 
under way, and before the experiments were discontinued the 
several specimens were reacting up to about the average of normal 
specimens fresh from the sea. That we have here modified be- 
havior growing out of environment, or experience, or both, seems 
more or less evident. Possibly the presence of strong light, asso- 
ciated with the tests referred to, had been operative m developing 
keener sensory powers. At any rate, the facts of modified be- 
havior are beyond question. ‘These serve to extend and confirm 
the experiments already mentioned, and warrant an assurance of 
a considerable degree of modifiability in these aspects of behavior 
upon the part of Hydroides. 
ASPECTS OF BEHAVIOR EXHIBITED BY THE TUBES 
In the former paper (p. 313), a brief paragraph and a few illus- 
trations were devoted to the problem of the significance of gravity 
as a factor in the behavior in these organisms. Additional facts 
