PARKER: THE REACTIONS OF METRIDIUM. 109 
sists of three zones: the tentacular zone, a broad, undulated peripheral 
band bearing the numerous tentacles characteristic of this species; the 
intermediate zone, marked by the absence of special structures and ex- 
tending from the inner boundary of the tentacular zone to the outer 
boundary of the lip zone; and, finally, the lip zone, occupied by the 
swollen lips, which surround the elongated mouth, at either end of 
which a siphonoglyphe is usually present. 
Aboral Disk and Column. — The aboral disk and column of Metridium 
have several peculiarities in common. By means of carmine, or other 
finely powdered materials, held ın suspension in sea-water, it was com- 
paratively easy to demonstrate the absence of active cilia from the 
surfaces of the aboral disk and of the column. And, further, when pieces 
of crab meat or filtered juice from crab meat was applied to either of 
these surfaces, no response was ever observed. I therefore believe that 
the column and aboral disk of Metridium are not ciliated, and are in- 
capable of being stimulated by the soluble constituents of the food. 
This latter conclusion has already been announced for other actinians 
by Nagel (92, p. 336). 
Oral Disk. — The oral disk, as its structure suggests, is far more 
complicated in its functional relations than the aboral disk and the 
column. In dealing with this region, it is best to consider its three 
zones separately, beginning with the outermost. 
The Tentacular Zone. — In a quiet, fully expanded Metridium, the 
tentacles are directed in a radial manner away from the mouth. Occa- 
sionally one or more tentacles may contract spontaneously, but as a 
rule they remain quietly expanded in the positions stated. Ifnow on 
such a tentacular zone a small amount of powdered carmine in sea- 
water be gently dropped, a momentary waving of the tentacles will 
usually be observed, followed by a period of quiescence, during which 
the carmine, matted together in threads as though by mucus, is slowly 
'arried from the bases of the tentacles toward their tips. If the tenta- 
cles upon which the experiment is made are on the outer edge of the 
tentacular zone, the carmine, when it arrives at their tips, will fall off 
beyond the oral disk. If, on the other hand, the tentacles in question 
do not reach the edge of the disk, the carmine will fall from their tips 
upon other tentacles, which in turn will transport it still farther toward 
the outer edge, till eventually it is carried beyond the disk. The carmine, 
then, must sooner or later find its way over the edge of the oral disk. 
The first movement noticed on applying the carmine, the swaying 
movement of the tentacles, is due to muscular action, and is called forth 
