110 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
without doubt by the mechanical stimulation that the particles of car- 
mine produce in coming in contact with the tentacles. At least, similar 
movements can be induced by gently touching the tentacles with a 
delicate glass rod. 
The second movement, the slow gliding of the carmine from the bases 
of the tentacles toward their tips, is produced by the cilia that cover 
the tentacles. These cilia, so far as I know, are in continuous vibration, 
producing currents that run from the base of the tentacle to its tip. 
The effect of their vibration can be easily observed on a tentacle cut 
from a living animal. Such a tentacle has a strong resemblance to an 
independent organism, and by means of its cilia glides slowly through 
the water with its base forward, a fact in accordance with the obser- 
vation that on attached tentacles the current produced by the cilia 
moves from base to tip. 
It will be seen from these observations that, when carmine is put on 
the tentacles of Metridium, two sets of movements are observable: first, 
a slight momentary muscular movement, due in all probability to the 
mechanical stimulation of the tentacle; and, secondly, a continuous 
ciliary movement, by which the carmine is carried to the tip of the 
tentacle and dropped off, but which, so far as I am aware, is neither 
induced nor retarded by the presence of the carmine. 
Another substance that produces a very marked effect upon the tenta- 
cles of Metridium is crab meat. If a small piece of the muscle of a 
crab be dropped on the tentacular zone of a quiescent actinian, the 
tentacles with which the meat comes in contact are thrown into active 
muscular movements, contracting on the sides next the meat so that 
eventually they come to envelop it. The tentacles thus stimulated 
finally take up a position with their tips pointed toward the centrally 
located mouth, instead of away from this opening, as in the experiment 
with carmine. As the cilia on these tentacles continue to wave in the 
usual direction, i. e. toward the tips of the tentacles, the particle of 
meat is moved toward the mouth and finally deposited on the lips, 
after which the tentacles slowly return to their original positions. 
It is clear from the preceding account that the response of the tenta- 
cles, when stimulated by crab meat, does not include an alteration in 
the action of the cilia, but merely a temporary reversal in the direction 
in which the tentacle usually points, a change of a purely muscular 
nature. This change might be regarded either as a response to a me- 
chanical stimulation produced by the contact of the food with the 
tentacles, or as the result of a chemical stimulation of the tentacles by 
