56 THE TROPISMS 
tion or pleasure is probably associated with the phototactie 
response. 
There are a few cases in which positively phototactic 
species swim backward instead of forward toward the light. 
An instance of this kind was found by Lyon in Palemonetes. 
Hadley found that larval lobsters swim with the head pointed 
away from the light whether they are postive or negative 
in their reaction. In the pycnogonid Anoplodactylus, 
Cole observed that in crawling toward the light the anterior 
end was in advance, but in swimming toward the light the 
animals moved approximately backward. 
Fiddler crabs form an exception to most phototactic 
animals in that in going toward the light the body is oriented 
sidewise instead of with its longitudinal axis in the direction 
of the rays. These animals are strongly positive and, like 
Ranatra, their response becomes stronger with longer ex- 
posure. They are timid animals and often a sudden move- 
ment of the light will send them scuttling away in alarm, 
but after following the light for some time they become 
more oblivious to other stimuli and slavishy follow it with 
less show of fear. Orienting movements are different from 
those used in ordinary locomotion which is not the case with 
most forms. Other animals may orient themselves by walk- 
ing faster, so to speak, on one side than on the other, but 
with lateral orientation special movements have to be per- 
formed in order to change the direction of locomotion. 
Here again it is difficult to apply the theory of forced 
orientation in its usual form, and we are led to conclude that 
the reaction to light is to a certain extent one of the pleasure- 
pain type. 
According to R&dl phototaxis has an intimate relation to 
vision. In a number of experiments Cole has found that 
reactions to light are influenced by the extent to which the 
