REACTIONS OF ARTHROPODS TO LIGHTS 483 



blue. In the blue and green pair of lights, the results are similar 

 to those of the green and blue already described. A larva ori- 

 ented in the blue is turned back at an angle by the green and 

 one started in the green is driven into the blue. The course 

 D E F (fig. 18) plotted by a larva in a blue-green pair is inter- 

 esting since the larva was oriented four different times and each 

 time it took practically the same angle with respect to the direc- 

 tion of the rays. It would be impracticable to reproduce repeti- 

 tions of the examples used in the foregoing account of the reactions 

 of blow-fly larvae. But since it is desirable to have more than 

 a single average record on which to base an opinion of a result, 

 the records of the respective pairs have been simplified and 

 condensed into diagrams. The construction and use of these 

 diagrams can be explained best by taking an actual example of 

 a reaction record, as for instance, red opposed to blue. In the 

 example (fig. 21, A) a larva was placed in a drop of methylene 

 blue at a and allowed to creep away from the red light to 6. 

 When at 6 the blue light was suddenly turned on and as soon 

 as the larva received the effect of the greater stimulus it took 

 the new direction he. In order to classify the records the approxi- 

 mate angle the larva took with reference to the direction of the 

 rays was determined in the following manner. From 6 as a 

 center, where the second hght was thrown on, an arc with a 

 radius of an arbitrary length of 8 cm. was drawn intersecting 

 the path, taken by the larva, at x. A line was drawn from h 

 parallel to the direction of the rays intersecting the arc at I. 

 The line h m was drawn perpendicular to the line h I thus cutting 

 ofT an arc of 90°. This arc which is now definitely oriented with 

 respect to the direction of the rays was divided into four parts 

 for convenience in combining the records. A circle of convenient 

 size (fig. 21 C) was then divided into four quadrants, each of 

 which, as the quadrant in figure 21 A, was further divided into 

 four parts and oriented with respect to direction of the rays. 

 The paths traced bj'- the larvae may now be classified on this 

 simple diagram by indicating the position of x on the arc of the 

 corresponding sector of the circle. Thus the record of the path 

 a 6 e of the larva in figure 21 A is indicated on figure 21 C by x' . 



THE JODRNAL OP EXPERIMENTAL ZOOLOGY, VOL. 14, NO. 4 



