RELATIVE STIMULATING EFFICIENCY OF LIGHT 149 



as strong as the other, deflected more toward the stronger beam 

 in the latter test than they deflected toward either beam in the 

 former test. An examination of table 1 shows also that the but- 

 terflies exhibited great variation in their reactions. For example, 

 the average angles made by the different insects in two beams of 

 equal illumination varied from -13.85 to +16.3 degrees. The 

 causes of this variation are discussed later. It is clear however 

 that in spite of great variation Vanessa when exposed to two 

 beams of continuous light which cross at right angles tends in 

 general to move toward a point between the sources, the location 

 of which depends upon the relative illumination in the beams. 

 This seems to indicate that the effect of light on orientation varies 

 with the illumination. 



This conclusion is supported by the results obtained with many 

 other organisms by Mast (1907 and 1911), Ewald (1913), Patten 

 (1914), and Loeb and Northrup (1917). 



IV. VARIATION IN REACTIONS TO LIGHT 



As stated above, Vanessa shows great variation in its reactions 

 to light. This is evident both in its reactions in continuous and 

 in intermittent light. Different individuals react differently, as 

 is shown by an examination of tables 1, 3, and 5. A given insect 

 also at times may show great variation in successive trials under 

 the same conditions. This is well illustrated in table 2. 



Table 2 shows that with the light from the two sources equal 

 the angles made in the individual trails varied from 14 to +21 

 degrees; that with the illumination in one beam three-fourths 

 that in the other the angles of the individual trails varied from 

 21 to +30 degrees; that with the illumination in one beam 

 twice that in the other the angles of the individual trails varied 

 from to +37 degrees; and that with the illumination in one 

 beam four times that in the other the angles made in the indi- 

 vidual trails varied from to +32 degrees. It is consequently 

 evident that Vanessa may show great variation under the same 

 conditions when reacting to two sources of continuous light. In 

 spite of this variation the average angle made increased, in gen- 



