372 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



small, but still readily visible, each consisting of a group of about 20 

 ocelli situated on the side of the head at the base of the antero-lateral 

 lobe. 



The animals were oriented in the proper position by placing them 

 within a small rectangular glass frame without top, the glass being 



covered with black paper 

 to exclude the light un- 

 til the pen thus made 

 was lifted up. The frame 

 was oblong, and just large 

 enough to enclose the 

 Oniscus easily without al- 

 lowing it to turn around. 

 With a little care the 

 frame could be readily 

 moved on the table (the 

 glass plate was not used) 

 to the position desired, 

 and with the animal 

 headed in either direc- 

 tion. When it was lifted 

 off, the animal was left 

 exposed to the lateral 

 influence of one or the 

 other or both of the 

 lights, as the case might 

 be, but free to move in 

 any direction. The rec- 

 ords indicate the place 

 where it crossed the sec- 

 ond of the three circles 

 inscribed on the table, — 

 the one with a radius of 

 ten centimeters. As the 

 animals usually took a 

 straight, or only slightly 

 curved course, this was 

 practically the distance travelled by them in each of the trials. 



The experiments with the lights used singly showed Oniscus to be 

 decidedly negative in the character of its reaction, but by no means so 

 strikingly so as the Tenebrio larva. In Oniscus, as may be seen from 

 an inspection of Table V, only 45 per cent to 51 per cent of the reac- 



FiGDRE 12. Frequency polygon constructed 

 from results witli Oniscus shown in Table V. A, 

 reactions to large light alone; B, to small liglit 

 alone ; C, to both lights used simultaneously (100 

 trials under each condition). 



