236 



BRADLEY M. PATTEN 



TABLE 3 



Measurements of the trails of figures 7 and 8 in tabular form. No. 16, 22/2/' 13, 

 made the trails photographed in figure 7 ; No. 22, 30/1/' IS, those of figure 8 



lights of unequal intensities. For if there is no deflection toward 

 either side following equal bilateral stimulation, the deflection 

 appearing under unequal bilateral stimulation may be regarded 

 as a true expression of the physiological effect of the difference 

 between the lights. 



The same method of taking the records at equality was used 

 with unequal lights. There is, however, one additional precau- 

 tion to be observed. A given side of the larva should be subjected 

 first to the stronger light in one pair of trails, and^first to the 

 weaker light in the second pair of trails, thus avoiding possible 

 cumulative effects such as might result if the stronger light acted 

 first on the more sensitive side in both pairs of trails. Asym- 

 metry of response, though not cancelling to zero in this case, is 

 checked out by the same method of running pairs of trails in 

 opposite directions. The stronger light acting on the more 

 sensitive side of the larva gives an abnormally great response; 

 when the direction of the crawling is reversed, the same light 

 acting on the weaker side gives a response correspondingly below 

 the normal. The excess of one response is equivalent to the 

 deficiency of the other, and the two average to a normal sym- 

 metrical response. 



This is clearly shown bj'- the two sets of trails photographed in 

 figures 7 and 8, which were made under the same percentage 

 difference in the lights, one by a symmetrical and the other by an 

 asymmetrical larva. Tabulating these trails side by side, by the 

 method already described, we obtain the results shown in table 3. 



