TRANSFORMATION OF HELIOTROPIO ANIMALS 269 



the dotted line cf l . In the shadow the animals were oriented 

 by the diffused light, and as the rays fell into the dish sym- 

 metrically from both right and left, the animals at first 

 moved in a line perpendicular to the plane of the window, 

 but as soon as they came out of the shade into the direct 

 sunlight, they did not turn about, nor did they even hesitate, 

 but followed in the direction of the sun's rays tof 19 where 

 they remained. The animals went thus from the "dark" 

 into the "light." 



To overcome the objection that the animals "love the 

 light," I made a third experiment, in which the conditions 

 remained just as in the experiment described above, except 

 that I placed the dish near the window in such a way that 

 the room side was in the shade and the side next the window 

 in direct sunlight. The animals which were on the window 

 side at the beginning of the experiment moved, as before, in 

 the direction of the sun's rays out of the sun into the shade, 

 where they remained. 



I wish to emphasize the fact that the animals remained 

 permanently on the room side of the dish, under all con- 

 ditions, no matter whether this part was in the sunlight, in 

 diffuse daylight, or in twilight. 



These facts show, first, that the larvae of Limulus move 

 in the direction of the rays of light, away from the source 

 of light; and, secondly, that they do so even when by so 

 doing they pass from shade into direct sunlight (or vice 

 versa). 



I call those animals which are oriented by light helio- 

 tropic, no matter whether, besides this, they execute pro- 

 gressive movements or not. But I wish to point out that not 

 every animal that is sensitive to light is also heliotropic. As 

 we shall see below, aside from the heliotropic, there is 

 another reaction to light, which does not consist in a direct 

 orientation of the animal. 



