542 
PHYSIOLOGY: LOEB AND NORTHROP 
ning of the experiments the pipette is filled with a dense suspension of 
larvae in sea water and then put with its point touching the bottom of 
the dish. The animals flow out in a fine stream which is narrow at 
the opening of the pipette and widens slightly, owing probably to the 
negative stereotropism of the animals. A glass plate (fig. 2) h i k I, 
which has a strong red line n o and a fine parallel line p g (cut with 
a diamond), is then put on the dish and so adjusted that g is in the 
middle of the stream f g of the animals. Then the angle a which p g 
makes wdth the perpendicular from ^ on a 6 is measured. This per- 
A 
o 
FIG. 1. 
pendicular is marked in the form of red line on the black base on 
which the glass vessel abed stands. The angle a is measured with a 
goniometer. When the lights are equal in intensity a should be 45°; if 
the two hghts have different intensities and if A be the stronger light 
a should become smaller with increasing difference in intensity. The 
individual measurements vary comparatively little, as long as the dif- 
ference in the intensity of the two lights is not too great; for this reason 
our observations do not go beyond a wider ratio of the two lights than 
10; 1. Table 1 gives the results. A is always the stronger light. 
