TRANSFORMATION OF HELIOTROPIC ANIMALS 269 
the dotted line ef,. 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 to /,, 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 larve 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. 
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