Mast, Light Reactions in Lower Organisms. 135 



had been demonstrated by me on the larvae of flies as early as 

 1887, in Wiirzburg, and often enough since. These facts seem 

 to have escaped several of my critics" [p. 2]. "When the diffuse 

 daylight which struck the larvae [Musca larvae] came from two 

 window^s, the planes of which were at an angle of 90° with each 

 other, the paths taken by the larvae lay diagonally between the 

 two planes. This experiment was recently published by an 

 American physiologist as a new discovery to prove that I had 

 overlooked the importance of tne intensity of light!" (p. 61-62). 

 "The direction of the median plane or the direction of the pro- 

 gressive movements of an animal coincides with the direction of 

 the rays of light, if there is only a single source of light. If 

 there are two sources of light of different intensities, the animal is 

 oriented by the stronger of the two lights. If their intensities be 

 equal, the animal is oriented in such a way as to have symmetrical 

 points of its body struck by the rays at the same angle" (p. 82). 

 "Attention need scarcely be called to the fact that if rays of light 

 strike the animal [larvae of Limulus polyphemus] simultaneously 

 from various directions, and the animal is able to move freely in all 

 directions, the more intense rays will determine the direction of 

 the progressive movements" (p. 268). 



It is evident without further discussion that the reactions of 

 Volvox do not fit the statements by Loeb, given in the above quo- 

 tations. Upon what experimental evidence does he base these 

 statements ^ Those with reference to orientation when the ani- 

 mals are subjected to light from two or more sources are based 

 largely, if not entirely, upon the following observations: (i) 

 "When the diffuse daylight which struck the larvae (Musca larvae) 

 came from two windows, the planes of which were at an angle of 

 90° with each other, the path taken by the larvae lay diagonally 

 between the two planes." (2) "Hawk moths were brought into 

 a room with the single window at one end, and a petroleum lamp 

 at the opposite end. It was found that, as twilight came on, the 

 moth flew to the window, or to the light, according to the relative 

 intensity of the one or the other at the point where the moth was 

 liberated." 



In the first place I am unable to understand how the direction 

 of rays can be ascertained in diffuse daylight coming through a 

 window; and in the second place, it is certainly not difficult to 

 see that an object placed between two windows, or between a 



