No. 420.] HISTORY OF STICHOSTEMMA. 983 
motion and constitute the chief organs of locomotion. If, 
. however, the forward movement ceases suddenly, or if the 
head be slightly drawn back, the cilia in the part affected stop 
their movement and remain nearly perpendicular to the body 
surface. If the animal remains quiet for a short time the 
cilia may begin to move slightly. It is difficult to determine 
whether this movement affords any definite impulse in either 
direction, but observation indicates that there is a very slight 
backward current along the body. When the head and ante- 
rior portions of the body are suddenly and violently drawn 
backward, as often occurs, or if the animal begins to move 
backward, the cilia of the contracting region are laid flat 
against the body, all pointing forward, and resume their usual 
position when the backward motion ceases. The body is at 
all times covered with a thin layer of slime, and it is possible 
that the turning forward of the cilia may be simply the result 
of the backward movement of the body through the slime. 
Observation of the head region, which is constantly undergoing 
contraction and extension, shows a beautiful play of the cilia, 
and often in the rapid but very slight contractions without 
actual backward movement, the cilia over a considerable area 
are all instantaneously turned forward against the body, per- 
haps to reappear almost immediately. The rapidity and uni- 
formity of their change of position render it probable that it 
is the result of a definite stimulation similar to that causing 
reversal of the cilia in many other forms. 
I have not been able to find any indications of actual 
reversed beating of the cilia causing backward movement of 
the body. The backward movement is apparently brought 
about wholly by muscular contractions, the cilia being laid 
against the body and pointing forward, so that they offer no 
resistance, but remaining motionless or making very slight 
indefinite vibrations. These conclusions agree well with those 
reached as the result of macroscopic observations on the mov- 
ing animal. Stichostemma does not appear to glide backward, 
but accomplishes this movement by violent muscular contrac- 
tions as described above. Except when the stimulation is 
very intense and sudden, it is more likely to turn the head 
