NO. 10 TROPISMS OF LEPIDOPTERA — McINDOO 3 



view. Loeb attempted to show that the behavior in plants and animals 

 is practically alike, and concluded that the behavior in animals is 

 largely controlled by external agents, and is influenced by internal 

 factors. He and his followers described reactions in animals in terms 

 of tropisms. 



There has been a controversy among various classes of scientists 

 in regard to the proper terminology to be used in connection with 

 tropic responses. Couch (6) proposes that the generic name, tropism, 

 be retained for all the classes, but that biologists and biochemists use 

 the words phototaxis, geotaxis, chemotaxis, etc., leaving the " isms " 

 to be used by chemists and physicists, and particularly the word 

 phototropism by the photochemist. 



Mast (57) informs us that the term tropism has been defined in 

 some 20 difl^erent senses. Since there is so much confusion about its 

 meaning, he proposes that we cease using it altogether, using instead 

 terms with more precise meanings as (p. 261) : " negative or positive 

 orientation or reaction to light, gravity, etc. ; photo-, geo-, etc., negative 

 or positive ; or merely negative or positive reactions to light, gravity, 

 chemicals, etc." In the following discussions these suggestions will 

 be frequently followed, and instead of saying that an insect is nega- 

 tively or positively phototropic or phototactic, it will be said to respond 

 or react negatively or positively to light, or to be photonegative or 

 photopositive. 



I. PHOTOTAXIS 



I. REVIEW OF LITERATURE 



(a) Definitions and problems in the study of light reactions. — The 

 terms heliotropism and phototropism have been generally used by 

 both botanists and zoologists, but as already mentioned, Couch pro- 

 poses that biologists use the word phototaxis, leaving the former terms 

 for the photochemist. Botanists still insist on using them, but recom- 

 mend that zoologists should say phototaxis and phototactic. According 

 to Mast (56, p. 253) the botanists are correct, because 



Organisms which orient and move toward or from a source of light are usually 

 termed phototactic, those which orient but do not move as phototropic, and those 

 v/hich do not orient but still react have been termed photopathic. 



Loeb, discussing both plants and animals, used the word helio- 

 tropism in his original German publications, in their English transla- 

 tions, and even in his latest papers. For our purpose here Loeb's 

 definition of phototaxis will suffice. He says (43, pp. 135, 139) : 



Heliotropism covers only those cases where the turning to the light is com- 

 pulsory and irresistible, and is brought about automatically or mechanically by 



