HELIOTROPISM OF ANIMALS 87 



Ilic direction of the rerfieal and turn their head* 

 There are, Itoicerer, also animals which orient ///r///.sv//v.s in 

 e.niefl// {lie rererxe manner anil turn their head* doirnirard. 

 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. 1 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 



O O O 



these compensatory after-movements in insects. 2 



r. 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 

 rii/lif in its progressive movements. These deviations are 

 gn-ater 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 unsyni- 

 niftrical. 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, 



1 MACH, Cniii'll/iiii-ii (/</ l.clin- run </// l{fii-c</i(ti<ixciiii>Jiii<htiiii<-n I Leipzig, IST.'i). 



2 The observations of Lyon and of R&dl suggest tin- po--ii>ilit.\ ih.u thr-c> piic- 

 IH) mi 'ii. -i < I- ! H -i ic I upon t hi- ey- of thc->c- animals. \Vlirn the eye-; arc' removed or black- 

 enc-il tin- reaei i'.n- o-a-i'. | I'."!.')] 



