38 THE TROPISMS 
In another’ experiment by Lyon fish were placed in a 
long bottle which was corked. When the bottle was pulled 
through the water the fish immediately swam opposite the 
direction of movement. If the bottle was allowed to flow 
down stream the fish would swim to the up stream end; 
if it was pulled up stream the fish would swim to the down 
stream end. It is evident that rheotaxis takes place through 
orientation to objects in the field of vision. In young 
lobsters Hadley has shown that rheotaxis is a sight response 
much as in fishes. In later stages when the lobsters keep 
closer to the bottom rheotaxis is gradually lost. 
Blinded fish may orient themselves to currents so long as 
they are in contact with the bottom of the stream, but when 
they leave the bottom they lose entirely their rheotactic 
response, unless different parts of the stream with which 
they come in contact have different velocities. 
Many insects tend to fly against the wind (anemotropism). 
This also is probably a sight reflex, since the insect receives 
pressure from the air only when flying against it. May 
flies, according to Radl, often. hover over one spot, slowly. . 
rising and sinking, but keeping their bodies facing the wind 
and their long fore-legs stretched forward. The same trait 
is shown by many insects, especially flies, even when there is 
no perceptible breeze. Often a group of flies will kcep 
hovering near one, and will move as one’s body moves always 
keeping away at about the same distance. Apparently 
we have to do here with an effort to maintain a certain 
relation to the visual field which so largely determines the 
rheotactic responses of fishes. 
It is obvious that under the head of rheotaxis phenomena 
have been included which are quite unlike in their causation, 
some of them being reactions to pressure differences, others 
presenting interesting points of similarity to phototaxis. 
