COMPENSATORY MOVEMENTS 39 
COMPENSATORY MOVEMENTS 
A class of phenomena having certain relations to rheotaxis 
are the so-called compensatory motions of animals. These 
may easily be illustrated by a common frog. If a frog be 
slowly rotated about a vertical axis it will turn its head 
and may begin to walk opposite the direction of movement. 
If it is tilted downward in front, the head will be raised, 
while if it is inclined upward, the head will be lowered. 
Various combined motions will be responded to by move- 
ments which tend to keep the head in the same position as 
before. 
A pigeon when slowly rotated on a horizontal turntable 
turns its head opposite the direction of movement until 
it reaches a certain angle with the body when it is suddenly 
jerked back to its original position. It immediately repeats 
the previous movement until its head reaches again the 
maximum angle when it is jerked back again as before. 
If the head is held during rotations, compensatory motions 
followed by regular jerking back movements are performed 
by the eyes. Mammals show similar movements, and mice 
and several other forms run around on the turntable opposite 
the direction of rotation. An interesting form of compen- 
satory movement is shown by the common domestic fowl. 
Hold an individual in the hands and move it slowly back 
and forth, up and down, or sidewise. If the fowl is not 
carried too far the head will keep in almost exactly the same 
position, the neck being often stretched out to its extreme 
length before the head follows the movements of the body. 
It was formerly supposed that in vertebrate animals 
compensatory motions were dependent on the semicircular 
canals, but it was found that these motions still persisted 
after the semicircular canals were plugged up or extirpated, 
or after the nerves supplying them were cut. The otoliths 
