Holmes, TJie Reactions of Ranatra to Light. 325 



stop to rub their eyes with their first pair of legs, using their 

 claws in what seems to be an effort to scrape off some foreign 

 object from the cornea. If a light is moved over an insect 

 when it is engaged in this operation the swaying movements of 

 the body will no longer be performed. The head reflexes are 

 also sometimes inhibited, but usually the head can be kept 

 moving about at the same time the insect is rather ineffectually 

 attempting to rub its eyes The swaying movements are like- 

 wise inhibited when Ranatra stops to rub its wings or any oth- 

 er part of the body. These actions may be caused by daubing 

 asphalt varnish upon the insect, when efforts are made to get 

 rid of the offending substance. As soon as the cleaning move- 

 ments are over the insect promptly reacts to light as before. It 

 generally makes no attempt to do two things at once. 



The phototactic response may also be inhibited by efforts 

 to obtain food. Ranatras which are swimming towards the 

 light can often be caused to discontinue their phototactic efforts 

 if several small insects are placed near them. If the phototac- 

 tic activities are very lively and vigorous it is more difficult to 

 divert the attention of the insect to the capture of prey. When 

 attention is once directed to seizing the smaller insects the light 

 is disregarded. When the prey has once been captured and 

 the Ranatra is engaged in sucking out its juices little attention 

 is paid to the light. The repast being finished the insect may 

 resume its positive response. 



- Efforts to go towards the light are frequently inhibited by 

 contact stimuli. When several individuals are put into a dish 

 of water near a window they commonly cease, after a time, to 

 swim towards the light and form a dense cluster in which they 

 lie at all possible angles to the direction of the rays. If now 

 the individuals are placed in separate dishes they soon show a 

 positive phototaxis. When placed together again they quickly 

 form a group as before. Contact stimuli not only inhibit posi- 

 tive phototaxis but they produce a negative reaction as we have 

 already seen : the latter tendency however, is often held in 

 check by the same cause by which it is brought about. 



Phototactic activities may also be checked by the sudden 



