12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



reduce the intensity, whereas white clouds in the sky but not over the 

 sun increase it by reflection from lo to 40 per cent over that of a 

 cloudless day. 



In view of the varying light values and other conditions involved in 

 phototactic experiments, the reader can appreciate the experimenter's 

 difficulties and can understand why it is so difficult to interpret the 

 results correctly. 



In bright light, although not direct sunshine, codling-moth larvae 

 of the first instar were found to be weakly photopositive, and their 

 reactions agreed in general principles with those described by other 

 investigators. None was found, however, to orient and to move with 

 mathematical precision as was stated by Loeb for certain insects. 



Larvae of the first instar, confined in an uncovered box in which 

 most of the light was reflected from the ceiling, moved in all direc- 

 tions. Recently hatched larvae placed on a table by a south window 

 and six feet from an east window, instead of moving directly toward 

 the south window, deviated toward the left (fig. i, A). This reaction 

 agrees with those described by other writers, for example Dolley (12), 

 when two sources of light at right angles are employed. 



In order to eliminate side lights a box, 18 inches long, 12 inches 

 wide, 12 inches high, and lined with a dead-black cloth, was con- 

 structed. One end and the top were left open. The open end faced 

 the south window while the experimenter, from above, traced the 

 tracks of the insect with a pencil. Since there was apparently no 

 difference between white paper and black paper as to effects of reflected 

 light on the insect, all tracings were made on white paper. The pencil 

 was moved gently a few millimeters behind the insect and this usually 

 did not affect the behavior of the larva, although in tracing the path 

 of photonegative insects care had to be exercised not to allow shadows 

 from the pencil to fall upon the insect. Recently hatched larvae, when 

 put in this phototactic box on either bright sunshiny days or on cloudy 

 days, oriented themselves and tended to move toward the direct rays 

 of light as illustrated in figure i, B, in which those tested before 

 noon deviated toward the left (No. p6) while those tested after noon 

 deviated toward the right (Nos. p8, pp). Many exceptions to this 

 tendency, which the writer cannot explain, were recorded, so no 

 definite rules can be stated. In order to be reasonably certain about 

 the light reactions of all the larvae tested, it was necessary to test each 

 one two or more times before drawing conclusions. 



Larvae of the second, third, and fourth instars were found to be 

 weakly photopositive to weak light (fig. i, C, Nos. 112a, lija, I2^a), 

 but indift'erent to strong light (Nos. ii2h, iijb, 124b). 



