116 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Stimulation of the lips induces a peristaltic movement of the gullet, 
and, if excessive, a contraction of the sphincter of the oral disk, but is 
never, so far as my experience extends, accompanied by a movement 
of the tentacles. These were the principal correlations observed in the 
muscular responses to stimulation by food. 
The looseness of the nervous organization in Metridium is well illus- 
trated by experiments that were made first by Nagel (’92, pp. 336 and 
337), and that I have attempted to carry out in the following way. 
Choosing a definite region in what, for convenience, we may call the 
right side of the tentacular zone of Metridium, I placed upon it a small 
piece of meat and recorded the time it took for this to be swallowed, 
I next placed on the same region a piece of bibulous paper soaked with 
dilute meat juice and again noted the time required for the animal to 
swallow this object. These operations were repeated in regular alter- 
nation with the results that are shown in the first column (Aug. 24, 
R. Side) of the following table. The inspection of this column shows 
that the time required to swallow a piece of meat varied from 40 to 
85 seconds, and that the variations in these periods form no regular 
series. The periods occupied in swallowing the paper soaked in weak 
meat juice form a series of intervals of increasing lengths till finally 
at the eighth trial the paper was not swallowed at all, the same being 
true of all subsequent trials. In other words, the successive application 
of a very weak stimulus is accompanied, not by the summation of the 
effects of stimulation, but by a gradual decline in these effects, till 
finally the response fails entirely. 
After having produced this effect upon the right lip, I repeated the 
experiment upon the left, with the view of determining whether the 
condition brought about in the right lip had spread to the left one. 
As the second column (August 24, L. Side) in the table shows, there 
was no evidence of such a result ; in fact, it took longer for the left side 
to become indifferent to the stimulus than it had taken for the right, 
instead of the reverse, as one might have expected. 
This double experiment was repeated on the same animal on August 
25, 26, and 27. As it was necessary to make up a new solution of meat 
juice each day, and as it was impossible to be certain that the strength 
was the same each time, the records for different days have no great 
value for comparison. I therefore give only the record for the last day, 
which is essentially similar to the intervening ones, and illustrates, even 
better than that of the first day, the extreme looseness, or even indepen- 
dence, of the nervous activities of the two sides of the animal. This may 
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