Holmes, The Reactions of Ranatra to LigJit. 3 1 1 



The method of sound production has been described by Torre 

 BuENO. The statement of this writer that the stridulation of 

 Ranatra was not previously described is not correct, for the 

 subject was briefly treated of by Locy^ in 1884. 



The instinct 6f feigning death, which is remarkably well 

 developed in Ranatra, will be described in a subsequent paper. 



III. Reactions to Light. 



General Features of the Phototactic Response. When Ran- 

 atras are kept in a glass dish of water near a window they are 

 usually to be found facing the light, often swimming towards it 

 and repeatedly colliding with the side of the dish and clawing 

 against the invisible barrier which blocks their course. These 

 movements may be kept up, with intervals of rest, all day. 

 When an artificial light is used the Ranatras may be caused to 

 swim in any desired direction by placing the light in the proper 

 position. In experiments with this species I have usually em- 

 ployed an ordinary 16 candle-power incandescent lamp attached 

 to a flexible cord of wire which permitted it to be readily mov- 

 ed about at will. The work was carried on in a darkened room 

 so that the specimens experimented with were exposed to light 

 only from this source. 



When Ranatras are taken out of water and laid on a table 

 they generally feign death, and, while in that condition, they 

 at first give no reaction to light. One may move the light 

 about near them or hold it almost against their eyes without 

 eliciting the least sign of a response. This apparent insensi- 

 bility, gradually wears away, and after some minutes the move- 

 ments of the light are followed by scarcely perceptible motions 

 of the head. By passing the light back and forth laterally over 

 the body the head may be caused to rotate laterally each time 

 the position of the light is changed. These are the first move- 

 ments that can be made to appear, and they grow more decid- 

 ed the longer the experiment is continued. A little later the 

 animal may be made to respond by vertical head movements 



'Anatomy and Physiology of the Family Nepidae, Am. Nat., 1884, p. 364. 



