4 A. C. IVY 



is present in the pigeon only to a slight and less pronounced de- 

 gree than in mammals. According to my observations, the av- 

 erage number of rotatory nystagmic movements for thirty pigeons 1 

 when rotated through an arc of ninety degrees at a speed of one 

 turn in two seconds was six, the minimum number being three, 

 the maximum ten. The average number of postrotatory move- 

 ments for the same group of pigeons when rotated ten times at a 

 speed of one turn in two seconds was eleven, the minimum being 

 four, the maximum twenty. The average duration of the af- 

 ter-nystagmus was five seconds. 



Hemi-decerebration in the pigeon has no effect upon nystagmus. 



Complete decerebration with even extensive injury to the 

 thalamus does not abolish the quick component of nystagmus 

 provided the temperature of the bird is kept normal. Rogers 

 ('18) has shown that the temperature of the decerebrate bird with 

 thalamic lesion must be kept normal in order to get normal de- 

 cerebrate behavior. In two such pigeons, whose body tempera- 

 ture fluctuated with the temperature of the surrounding air, it 

 was found that the quick component of nystagmus disappeared 

 at 34°C. in one and 35°C. in the other, while deviation persisted. 



Rabbits. True vestibular nystagmus is present in the rabbit. 

 The average number of rotatory movements for eight rabbits 

 when rotated though an arc of ninety degrees at a speed of one 

 turn in two seconds was five, the minimum being four, the maxi- 

 mum seven. The average number of postrotatory movements 

 for the same group of rabbits when rotated at the same speed 

 was sixteen, the minimum being seven, the maximum twenty- 

 four. The average duration of the after-nystagmus was eight 

 seconds. 



Some rabbits show a marked variation in the number of move- 

 ments and the duration of the after-nystagmus, although they 

 were rotated at the same rate of speed and other factors were con- 

 trolled. One of the rabbits varied from seven to twenty-two 

 movements, or from four to ten seconds, during the course of 



1 The pigeon's head should be fixed so it cannol be moved. The pigeon has a 

 method of shaking and twisting its head which markedly inhibits the number 

 of the movements and duration of the after-nystagmus. 



