76 



TROPISMS 



worked out quantitatively by Bradley M. Patten on a 

 negatively heliotropic animal, the full grown larva of 

 the blowfly. 412 , 413 The source of light was at G (Fig. 28) 

 (one or more Nernst lamps of measured candle power), 

 a portion of light from these lamps passed through the 

 screens d and d f to the mirrors M and M\ set at a definite 



Fig. 28. — Diagram of apparatus used to produce differential bilateral light stimulation. 

 O, five 220-volt Nernst glowers; M and M', mirrors; / and /', central point of mirrors; O, 

 center of observation stage; dotted lines, central ray of beam of light from the glowers 

 reflected to O by the mirrors; d and d' , screens with rectangular openings; s and s', light 

 shields; a and b, 2 c.p. orienting light with screens. (After Patten.) 



angle so that the rays were reflected to the observation 

 point 0. The two beams of light reaching were of the 

 same intensity. With the means of one of the lights at 

 a or b the animal was first caused to move across the 

 field at right angles to the rays reflected from the mir- 

 rors M and M'. The animals first started in this direction, 

 then came suddenly under the influence of the light re- 



