238 BRADLEY M. PATTEN 



The total response of the four trails is nearly the same for the 

 two larvae. Dividing the total response by the number of trails 

 made, the average trail of the individual is obtained. This is 

 for the symmetrical larva (No. 16, 30/2/'13), 8°, and for the 

 asymmetrical larva (No. 22, 30/1/' 13), 10.25°. A similar case 

 at 50 per cent difference is illustrated in figures 19 and 20, page 

 260. 



The conformity of these averages from such apparently different 

 trails, together with the similar case already considered at 

 equality, is convincing as to the completeness with which the 

 disturbing effect of the asymmetry has been eliminated. I have 

 laid special emphasis on this matter of asymmetry and the 

 method of dealing with it, because it is important that the final 

 results should be free from the possible cumulative effect of in- 

 dividual eccentricities. The average reaction of a large num- 

 ber of individuals, tabulated in this manner, is used to establish 

 the angle of response under each set of conditions. 



In spite of the precautions used in obtaining the records, ex- 

 tremely aberrant responses occasionally appeared. In all the 

 tables, the average deviation of the individual responses from the 

 mean of the set was computed, and when any records showed a 

 departure of more than three times the 'average error,' they were 

 not entered in the tables. This selection was not applied to 

 separate trails but to the records of a larva as a whole. Either 

 all the trails of a larva were accepted, or the larva was thrown 

 out as an extreme variant and none of its trails w^ere used. For 

 these discarded trails, the trails of a fresh, tested larva, run 

 under the same conditions, were substituted. The tables were 

 computed both with and without this correction and the difference 

 was found to be very slight, as the records exceeding three times 

 the 'average error' were very uncommon, many of the tables not 

 showing a single case. 



