HELIOTROPISM OF ANIMALS 8&7 
the direction of the vertical and turn their heads upward. 
There are, however, also animals which orient themselves in 
exactly the reverse manner and turn their heads downward. 
To this class belongs the garden spider, which we find hang- 
ing in this position in the center of its web for hours. I 
found the same behavior in one of the Diptera, which I have 
not yet classified. 
5. If a beetle or a house fly (from which the wings have 
been removed) is placed on the disk of a centrifugal machine, 
which is rotated slowly, the insect turns its body around the 
same axis, but in an opposite direction to that of the revolv- 
ing plate. 
If the velocity of the machine is increased, these compen- 
satory movements cease. These animals therefore behave in 
this respect exactly as Mach claims vertebrates behave which 
possess a labyrinth.’ But while the movements of vertebrates 
continue for some time after the movement of the centrifugal 
machine has ceased, but in a sense opposite to those occur- 
ring during rotation, I have never been able to bring about 
these compensatory after-movements in insects.” 
6. When one hemisphere of the brain of a house fly is 
removed the same disturbances in orientation appear as after 
the same operation on a rabbit. The fly from which the left 
hemisphere has been removed moves continually toward the 
right in its progressive movements. These deviations are 
greater or less according to the success of the operation. I 
showed in an earlier paper that the turn-table reactions of 
dogs and rabbits deprived of a hemisphere might be unsym- 
metrical. If a fly which has lost the left half of its brain is 
placed on a rotating disk, we find that on turning the disk 
in the direction of the hands of a watch as seen from above, 
1Macu, Grundlinien der Lehre von den Bewegungsempfindungen (Leipzig, 1875). 
2The observations of Lyon and of Radl suggest the possibility that these phe- 
nomena depend upon the eyes of these animals. When the eyes are removed or black- 
ened the reactions cease. [1903] 
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