124 OTOLITH ORGANS AND SEMICIRCULAR CANALS 



clearness with which operations may be performed through the trans- 

 parent cartilage of the skull, and the fact that bleeding can be almost 

 wholly avoided and that the fish recovers readily from the shock of 

 the operation. 



In my experiments it has been necessary to use as indices of results 

 the well known compensatory movements which occur on rotation, the 

 righting reaction, and the general state of equilibrium. The com- 

 pensatory movements of the eyes and fins of the dogfish, as first 

 described by Loeb,^ are remarkably constant. I have made especial 

 use of the eye movements which may be described briefly as follows: 

 if a dogfish is held in its normal resting position, belly down, and 

 longitudinal body axis horizontal, the eyes assume a characteristic 

 resting position, symmetrical to the body. This position of the body 

 I shall refer to as normal and the position of the eyes as the primary 

 position. If the animal is rotated to the right around its longitudinal 

 axis, the eyes make complementary movements of such character 

 that they tend to preserve their original position in space; that is, 

 the right eye is elevated and the left eye is depressed. If the rotation 

 is around the transverse axis, head incKned downward, both eyes 

 appear to rotate on their axes by a wheel-hke movement so that the 

 anterior pole of each eye is elevated and the posterior pole is depressed. 

 If the animal is rotated backward around its transverse axis both 

 eyes make a compensatory wheel-hke forward rotation. If the animal 

 is rotated about an obliquely placed horizontal axis the compensatory 

 movement is a resultant of the effects which would be produced by 

 the rotations around the two axes of reference. These compensatory 

 movements are made during the rotation, but if the abnormal body 

 position is retained, the complementary position of the eyes is also 

 retained. It is seen, of course, that as long as the animal is kept 

 in the abnormal position there is a constant force; namely, the force 

 of gravity, acting upon its body elements in an unaccustomed direction. 

 If the animal is held in the normal position and the body is then 

 rotated around its dorsoventral axis, both eyes turn by a conjugate 

 movement in the opposite direction; that is, if the head is swung to 

 the right both eyes turn to the left, and if the head is swung to the 



■•■ Loeb, J., Ueber Geotropismus bei Thieren, Arch. ges. Physiol., 1891, xlix, 175. 



