PARKER: THE REACTIONS OF METRIDIUM. 115 
As in the case of the tentacles, 1 could distinguish for the lips only 
two classes of substances: materials to which the lips were indifferent, 
such as carmine, India ink, paper pellets, sand, sugar, quinine, and 
pierio acid ; and materials that called forth muscular responses and 
ciliary reversals, such as meat and meat juice, and possibly India-rubber. 
When a small piece of white India-rubber, such as is used in making 
white rubber tubing, was put upon the lips of a Metridium, it usually 
caused a reversal of the ciliary action, and was swept into the mouth; 
sometimes, after moving inward, it would turn and pass outward to be 
discharged finally from the oral disk by the tentacles, 
It is obvious from the foregoing account that not only the tentaele, 
but also the lips of Metridium are capable of being stimulated by the 
soluble constituents of food. This conclusion is at variance with that 
held by Nagel, namely, that the tentacles are the only parts of an ac- 
tinian capable of being thus stimulated, but coincides with Loeb's belief 
that other organs than the tentacles can be stimulated by the soluble 
parts of the food. The diserepaney between my own conclusions and 
those of Nagel might be attributed to the fact that we worked upon 
different genera of actinians; but I am not inclined to accept this ex- 
planation, for Loeb, who studied many of the same forms that Nagel 
did (Actinia, Adamsia, Anemonia, eto.), obtained results with which 
mine agree.. I therefore believe Nagel to have been mistaken in his 
general conclusion. Further, my results show that, as Loeb has inti- 
mated, the appropriation of food by an actinian is an act partly muscu- 
lar and partly ciliary, and not purely muscular, as described by Nagel. 
Correlation of Movements, — Of the two kinds of responses in con- 
nection with the taking of food in Metridium, the ciliary and the mus- 
cular, only the latter shows evidence of nervous control, and I now turn 
to this for further consideration. As already pointed out, this response 
appears in connection with the stimulation of the tentacles or lips by 
means of the soluble constituents of the food. Stimulation of the tenta- 
cles is followed by movement of the tentacles, peristaltic movements of 
the gullet, and, if the stimulation be excessive, by a contraction of the 
sphineter of the oral disk. I have already pointed out the marked 
antonomy ofa single tentacle. Although the tentacles are centres from 
which nervous impulses may proceed to the gullet and the sphincter of 
the oral disk, I have been unable to convince myself that one tentacle 
could influence another through nervous connections; I have never 
observed a response that could not be explained on the assumption of 
a direct stimulation of the tentacles. 
