Holmes, TJie Reactions of Ranatra to Light. 347 



for a higher animal. The phototactic movements of the crea- 

 ture are not merely stereotyped reflexes which the insect is in- 

 voluntarily forced to perform. To get to the light is an end 

 which is arrived at if not by one method, then by another. 



The phototaxis of Ranatra comes, to a considerable degree, 

 I believe, under the pleasure-pain type of response. Why a 

 creature should be so constituted as to derive satisfaction from 

 so stupid a performance as wildly chasing after a strong light is 

 a subject that need not concern us in our present quest. The 

 behavior of Ranatra presents the essential features of the pleas- 

 ure-pain reaction of higher forms, and we are justified, I believe, 

 in classing it under this heading. The fact that Ranatra will 

 continue to follow the light even when it is brought thereby into 

 a situation that produces a fatal effect does not necessarily ex- 

 clude its conduct from this category. While it is true that ani- 

 mals tend to continue reacting towards stimuli that produce a 

 beneficial effect and away from stimuli that bring about delete- 

 rious results, the rule is by no means absolute. In a state of 

 nature Ranatras probably are rarely, if ever, exposed to condi- 

 tions that produce as strong positive phototaxis as they show 

 under artificial conditions in the laboratory ; and there seems to 

 be no benefit that possibly can be derived from their strong 

 propensity to seek the light. This propensity, like that of hu- 

 man beings for certain stimulants and narcotics, has probably 

 not been evolved by natural selection for any useful purpose, 

 but is an incidental result of the way the creature is constituted. 

 Whether there is any connection between pleasure-giving acts 

 which tend to be repeated and acts which secure some benefit 

 to the organism closer than that which would naturally be 

 established through selection may well be doubted. Neither an 

 animal's direct reflexes nor its attempts to seek some source of 

 gratification infallibly lead to securing some benefit; and the fact 

 that a certain kind of behavior is persisted in until it brings 

 about fatal effect does not ipso facto enable us to decide under 

 which of these categories it falls. 



It is the apparent telecity in the efforts of Ranatra to reach 

 the light which it is difficult to understand according to a purely 



