l6o yoiirnal of Comparative Neurology and Psychology. 



was decreased to X and (T -) increased to T, the colony became 

 neutral. The point where this took place is represented in the 

 path by the sharp curve. But why did the colony not remain 

 neutral ? Because it was in a supra-optimum light intensity and, 

 therefore, in accordance with our assumption, X continued to 

 decrease and T to increase, X^T resulting in (X -) and (T +) 

 compounds w^hich caused the organism to become negative and 

 it remained so to the end of its course. Had the aquarium been 

 wider it would have reached a point at which it would have been 

 neutral in an optimum light intensity. If the reactions are regu- 

 lated as assumed, it would have reached this point as follows: 

 (X-)^(7"+) expresses the condition of the colony as it pro- 

 ceeded from the source of light toward c\ but as the intensity 

 decreases the rate of formation of X increases and that of T de- 

 creases until the colony reaches the point of optimum intensity, 

 when the rate in opposite directions is equal (X -)^(^T +). The 

 organism, however, is still negative at this point, since it con- 

 tains (X -) and (^+) substances, and it therefore proceeds into 

 a region of sub-optimum intensity, where (X -) increases and 

 (^+) decreases (X -)^(T +). This results in X ^nd T sub- 

 stances and the colonies consequently become neutral. The 

 chemical reaction, however, continues to favor the formation of 

 X, since the light is sub-optimum, and this soon results in 

 (X +) and (T -) substances, which causes theorganismto become 

 positive. It therefore turns and proceeds toward the source of 

 light again, but owing to the accumulation of (X +) and (T -) 

 substances, it passes the region of optimum intensity before 

 it becomes neutral, and therefore becomes negative again. It 

 may be conceived to thus pass back and forth several times, like 

 a pendulum, before being neutral in the optimum region. 



In accordance with our assumption, the conditions of the colony 

 in producing the path B could be represented as follows: 



(X +)^(T -) from c to the beginning of the curve; 

 (X) ^(T) at the point in the curve nearest the arc; 

 (X —)^(T +) from this point to ti; 



(X -)^(T +) from 71 to the beginning of the curve beyond; 

 (X) ^(^) at the point in the curve farthest from the glower; 

 and (X +)^(^T) from this point to ?/, the end of the course. 

 We have thus presented a formal explanation of these paradox- 



