336 University of California Publications. | ZooLoGy 
above. I had found previously that when stems relieved of 
hydranths and the weight of sand grains adhering to the hold- 
fasts were supported at their distal ends, they would assume 
the normal vertical orientation, proximal end down. Last March, 
the experiment was repeated many times, with special precau- 
tions against errors. Fresh animals were used, and their distal 
ends were fastened by a single loop to a rigid thread. The sup- 
port thus afforded was secure and ample for various movements. 
In every case, without regard for the amount of holdfast pres- 
ent, the unsupported proximal end travelled wpward and came 
to rest only when the stem had reached a position approximately 
vertical, but wpside down. 
Comparing this result with the movements of stems attached 
by the proximal end, either resting on or hanging from the sub- 
strate, it is obvious that no reversal of behavior in the axial cells 
need be assumed. The variable factor is connected with the point 
of support. 
By the foregoing observations, Corymorpha seems to be re- 
moved from the category of animals for the elucidation of whose 
behavior none of the familiar mechanical explanations of geo- 
tropism seem to apply. Its geotropic reactions appear now to 
accord with the theory which Davenport formulated with refer- 
ence to the geotropism of free-swimming organisms. There is 
a difference between the resistance encountered by the stem as it 
moves upward (friction plus weight) and the resistance it en- 
counters when it moves downward (friction less weight). This 
difference is expressed in the stem by a tension on its upper 
side when it is inclined in any degree from the vertical. There 
is no tension on the lower side of the stem unless it be hanging 
downward at some angle; in which ease it never equals the ten- 
sion on the upper side except when the stem is vertical, its posi- 
tion of rest. 
The evidence formerly presented in favor of the view that 
the axial endoderm cells, and not muscles, govern the geo- 
tropie orientation of the stem, has been strengthened to some 
extent by a further experiment. In my original experiments, 
euts were made at frequent intervals half way through the stem 
. — —— “or 
