EXPERIMENTS WITH VIBRATING CILIA. 643 
lower. In this case, while the lower cilia tend to move the upper 
piece from side to side, those of the upper tend to move this 
lengthwise of the lower. The direction which fhe upper piece 
takes, is a resultant one, viz., intermediate between the two. 
Experiments in air. Though the tissues of the gills of 
Unios and Anodontas are quite soft and incapable of resisting 
other than very light weights, they will nevertheless carry small 
discs of paper supporting a bristle, on the top of which is a small 
pellet of cotton or a flag of tissue paper. In order to show the 
flag more distinctly, a board painted black should be nailed to the 
edge of the one on which the gill rests, to make a back ground. 
With this precaution the experiment may be seen over a large 
room. To mark the distance traversed, a pointer of white paper 
should be set up on the board supporting the gill and at the be- 
ginning of the experiment, the end of the pointer brought in con- 
tact with the end of the flag on the gill. When left to itself, the 
disc on the gill with its flag at once begins to move to the opposite 
side and the flag is seen to recede from the pointer. The distance 
traversed may be increased to several inches, by placing two or 
more gills side by side, the free edge of the first slightly overlap- 
ping the cut edge of the second, etc. 
The mucous membrane from the roof of the mouth of frogs, is 
much more solid than the gills of Unios, and the cilia vibrate 
with much greater force. Different ciliated membranes exert very 
different degrees of force, but we have found none better suited 
for experiments than that just mentioned; especially, when taken 
from the mouth of the bull frog which gives a large surface. It 
has the advantage, too, of keeping up its activity for twenty-four 
hours or more, after being detached from its natural connections, 
if only kept cool and moist. For moistening it water answers 
sufficiently well, but the serum of the blood of the frog is still 
better. 
The attention of the writer was first called to the possibility of 
moving weights much larger than was supposed possible by notic- 
ing the ease with which a piece of skin which was accidentally 
placed upon the ciliated membrane was swept off. By loading 
the piece of skin with weights the mass moved was found to 
~ unexpectedly large. 
In making experiments for the purpose just mentioned we have 
adopted the following method. The mucous membrane, being 
