230 Herbert W. Rand 
tainly is not, for the following reasons. The form of the reversed 
tentacle, as shown in Fig. 17, is exactly what would be expected as 
the direct result of the mechanical pressure. It does not require 
any special contraction of the tissue in the vicinity of the free 
proximal end. ‘The tentacle is a hollow cylinder whose wall con- 
sists of very thin and elastic tissue. Previous to the introduction 
of the pressure the whole tentacle was in a state of uniform and 
extreme contraction. Slight pressures, such as induced extension 
of a piece of tentacle attached to the hydrostatic tube by its prox- 
imal end, produced no visible effect in this case. By pressure of 
8o mm. the contraction of the tissues was forcibly overcome. The 
tentacle became more or less distended throughout its entire 
length. But directly at the free proximal end there was less dis- 
tention simply because there was less pressure owing to the prox- 
imity of the opening through which the contained water escaped. 
On the other hand, the form of the piece of tentacle attached to the 
pressure tube by its proximal end is not such as would result 
passively from internal pressure. In this case extension often 
occurred under pressure too slight to produce any appreciable 
stretching of the tissues, and, further, the complete closing of the 
free distal end and the formation of the nipple cannot possibly 
be direct mechanical results of the internal pressure. We may 
safely conclude, then, that under the conditions of the experiment 
with the hydrostatic tube the free distal cut end executes certain 
special contractile activities which result in the forming of the 
nipple and the closing of the end while the rest of the tentacle is in 
a state of more or less relaxation. Its behavior is like that of the 
free distal cut end of a tentacle which is normally attached to the 
column. But the free proximal cut end, under the same condi- 
tions of experiment, does not exhibit any intrinsic activity which 
differentiates it from the rest of the tentacle. “The entire tentacle, 
in a state of persistent and extreme contraction, exhibits, like any 
inanimate structure, only passive changes of form as the direct 
mechanical effects of internal pressure. 
In the behavior of a normal tentacle certain expressions of po- 
larity are evident. One is to be seen in the directive stroke of the 
cilia. Another, and a very conspicuous one, is afforded by the 
