88 STUDIES IN GENERAL PHYSIOLOGY 



the fly makes slight or only weak compensatory movements 

 Yet when the disk is turned in the opposite direction the fly 

 reacts very promptly (apparently even better than before the 

 operation). After destroying both hemispheres or ampu- 

 tating the head I no longer obtained compensatory move- 

 ments in the fly. The experiments of Mach show that the 

 compensatory movements of vertebrates emanate from the 

 head ; according to Mach, the labyrinth is to be considered 

 the essential organ. Such an organ, however, does not 

 exist in the head of a fly. 



7. If the halteres are removed from a fly, it can no longer 

 fly upward ; in the attempt to fly it immediately falls to the 

 ground, where it frequently tumbles about. Gleichen- 

 Russwurm established this fact during the last century. I 

 found that such a fly reacts normally on the centrifugal 

 machine. The destruction of the halteres does not there- 

 fore have the same effect as the destruction of the labyrinth 

 in frogs, birds, or mammals, in which, according to the 

 experiments of Hogies and Schrader, compensatory move- 

 ments cease when the labyrinth is destroyed. The conjec- 

 ture expressed by others, and by me in my first publication, 

 that the direction of sound has an influence on orientation 

 has thus far led me to no new facts. 



8. I have not yet been able to demonstrate compensatory 

 movements on the centrifugal machine in caterpillars, Musca 

 Iarva3, and snails. 



