Holmes, The Reactions of Ranatra to Light. 327 



havior was essentially the same. Two specimens seemed to respond when the 

 light was moved near them but when the rays were passed through water before 

 reaching them no response could be evoked. It is probable, therefore, that their 

 movements were the result of stimulation by heat. Ranatras with the brain cut 

 through the middle, like those with the brain removed, are very sensitive to all 

 sorts of stimuli, and they are set into action by causes which would produce no 

 manifest effect in a normal individual. 



Bethe^ found that hemisecting the brain of Carcimis caused 

 the phototaxis of the animal to disappear, although most of its 

 other responses took place in a normal manner. I have found 

 the same in several species of insects^. In the amphipod Talor- 

 cJiestia longicornis, which has a remarkably strong positive pho- 

 totaxis, hemisection of the brain is followed by a complete loss 

 of the power of orientation. Sensitiveness to light, however, 

 is not entirely destroyed. If when a specimen is resting quiet- 

 ly in a shaded spot a beam of light filtered through an alum 

 cell is thrown upon its eyes it usually responds by a few irregu- 

 lar movements. Since a large part of the fibers of the optic 

 nerves cross in the brain, hemisection of this organ cuts off the 

 main path of the impulses concerned in orientation to light. 



g. The Effect of Covering the Anterior Half of the Eyes. 

 Ranatras with the anterior surface of both eyes blackened over 

 walk with the head strongly upturned and the anterior end of 

 the body high in the air. Sometimes they stand nearly vertic- 

 ally, and several times I have seen them fall directly over back- 

 wards. Even when going towards the light the anterior part of 

 the body is elevated, but not so much so as when the light is 

 held above or behind the insect. When the light is moved 

 backward and forward above the insect the body sways to and 

 fro, and the head responds with the usual vertical reflexes. 

 When the light is behind the insect the head and front part of 

 the body are much elevated ; if now the light is carried to the 

 front the creature bows down only for a short distance instead 

 of assuming the grovelling attitude of a normal individual in the 

 same situation. 



^Archivf. mik. Anat. 1897, 50, 617. 

 ''■Am. Jour. Physiol. 1902, 5, 211. 



