HELIOTROPISM OF ANIMALS 18 
on the other hand. If the law had reference only to white light, 
and not also to colored light—red, blue, etc.— which is, however, 
by no means always the case, one might at first be inclined to be- 
lieve that the animals which prefer red avoid mixed light because 
it contains many of the hated short waves of the blue and violet 
light; for this very reason it would be more agreeable than dim 
light to the animals which prefer blue, for dim mixed light is poor 
in all rays, and therefore also in blue. Yet the objection might be 
raised against this explanation that mixed light contains as much 
red for those animals which prefer red as it contains blue for those 
animals which prefer blue. Yet this objection could again be 
weakened by the assumption that, since the animals which prefer 
red also prefer darkness, they prefer a minus of their chosen color 
to a plus of the color they dislike. 
Graber finally considers it best “‘to await further investi- 
gations in a field where great darkness still prevails.” We 
see that Graber in regard to the effects of monochromatic 
light again establishes a contrast in effects where, as we shall 
see, a similarity exists. Graber was prevented from cor- 
rectly interpreting his results by attributing the movements 
of animals to sensations instead of to physical causes. If 
he had given up the anthropomorphic standpoint, he would 
soon have discovered that his experiments show that the 
more refrangible rays are more effective in causing the 
orientation of an animal than the less refrangible ones. 
In none of the investigations of Bert, Lubbock, or Graber 
has the influence of the direction of the rays on the orienta- 
tion been studied. Graber, for example, took it for granted 
that an animal moves to the light because, as he expressed 
it, “it is fond of the light” or “the white.” If it moves 
in the opposite direction, it “is fond of the dark.” Lubbock 
remarks incidentally that “ants do not like light in their 
nests, probably because they do not deem it safe.” 
This sums up the opinions and results of the authors who 
sought to explain anthropomorphically the phenomena which 
interest us here. 
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