PHOTOTAXIS 51 
Amphipoda are usually positively phototactic while the 
aquatic species are negative it occurred to me to try the effect, 
of throwing terrestrial forms into water. Specimens of 
Orchestia agilis which were very strongly positive were 
employed. As soon as they were in the water they all 
immediately became strongly negative and remained so 
for days in various intensities of light. That the trans- 
" formation is not due to change of temperature was shown 
by the fact that the same result was obtained whether the 
water was warmer or colder than the air, or at the same 
temperature. It is not improbable that it is the stimulus 
of contact afforded by the water that caused the reversal 
of the response. 
In the water scorpion Ranatra contact stimuli were found 
to have a very marked effect on the insect’s reaction to light. 
Handling these creatures throws them into a death feint 
which entirely inhibits, for a time, all phototactic response. 
It frequently happens that on recovery from the feint there 
is a negative response which later changes to positive. 
If specimens which are swimming at the end of a dish nearest 
the light are simply picked up by the breathing tube and 
dropped back into the water they immediately begin 
swimming with equal vigor in the other direction. They 
may be caused to reverse their phototaxis in this way 
repeatedly. The same effect can be produced if they are 
seized or stroked while under the water. Specimens which 
are making frantic efforts to go toward the light when in 
the air may be caused to become negative by simply dropping 
them into water. When taken out they usually show a 
marked negative response for some minutes, but later be- 
come positive. 
The method by which animals orient themselves to light 
naturally varies with their nervous and muscular organiza- 
