334 University of California Publications. [ ZooLoGy 
after which, strong irregular movements toward and away from 
the mouth appear. The proboscis, which carries the distal ten- 
tacles to the number of about fifty in a crown around its summit, 
may react to mechanical stimuli, directly or indirectly applied, 
by bending in the direction of the stimulus. 
These reactions of tentacles and proboscis constitute an effi- 
cient prehensile mechanism. A small object which happens to 
stimulate a proximal tentacle on its oral side is at once swept 
toward the mouth. The distal tentacles, which may be carried 
toward it by the bending of the proboscis, then move outward, 
meeting and transporting it by a subsequent inward movement 
to the mouth. 
All the motions thus far deseribed are due to muscular con- 
tractions. Locomotion is produced, as in Hydra, by the activi- 
ties of amoeboid cells at the base of the stem. And the circu- 
lation of fluids in the coenosareal canals is accomplished by the 
usual ciliary action, supplemented by the expansions and con- 
tractions of the proboscis and stem. 
Aside from these types of motion, the stem exhibits a marked 
geotropism, assuming when at rest a vertical position. This 
orientation does not appear to be dependent in any way upon 
museular activity. The behavior not only of the stem as a whole 
but of pieces of one-eighth or one-tenth its length from the base 
or various other regions, indicates that the stem is everywhere 
sensitive to the stimulus of gravity and furnished with an effi- 
cient mechanism for bringing about a response. This mechanism 
is expressed, I believe, in the large, highly vacuolated cells of 
the endodermiec axis which forms the core of the stem. Changes 
of orientation, according to this view, are produced by relative 
changes in the turgidity of such cells on opposites sides of the 
stem. Whether the orientation is to be reckoned as a contrac- 
tion phenomenon, though this is probable, cannot be said defi- 
nitely at this time. It is indeed a fact that the axial cells may 
not only decrease in size, as when the stem is shortened, but also 
increase in size, as when the stem is lengthened without loss in 
diameter. 
+ a ae Oe capt a cn ema 
