THIGMOTAXIS OR STEREOTROPISM 35 
pseudopod. Such a reaction is of evident service to the 
Ameeba in leading it into contact with objects where it 
secures food and protection. The process of food taking 
itself is probably dependent to a certain extent upon a 
thigmotactic motion. Strong contact such as striking a 
pseudopod with a needle causes the reverse or withdrawing 
reaction. By repeated application of the stimulus to one 
side Amceba may be driven about in any desired direction. 
Parameecia were found by Jennings to react to contact 
by collecting against solid objects. Often bits of substance 
are fairly coated by these infusorians. The cilia in contact 
with the object cease beating and stand out at right angles 
to the body while the cilia of the oral groove and sometimes 
also in other parts of the body, continue their movement. 
Among the hypotrichous infusoria the tendency to keep in 
contact with solids is very strong. In these forms the cilia 
on the under side of the body are metamorphosed into cirri 
which are employed in running about over objects much in 
the same way as an insect uses its legs. An Oxytricha is 
described by Verworn as happening to get upon the round 
egg of the clam Anodonta. It ran about for hours unable 
to leave the surface since the egg rested on the bottom at 
only one point. 
The infusorian Loxophyllum is usually engaged in gliding 
about on its right side. It is apparently indifferent as 
regards orientation to gravity, as it will move about on the 
under side of a surface film with its right side uppermost 
as well as on the bottom. When turned over on its left 
side it rights itself in several different ways. Even small 
pieces show the same tendency to keep the right side in 
contact with solids and they will also right themselves 
when turned over. Much of the righting movements of the 
lower animals consists in the effort to keep a certain side in 
