TRANSFORMATION OF HELIOTROPIO ANIMALS 285 
pendently of the light. Polygordius larvee usually swim at 
the surface of the water when positive, while in their nega- 
tively heliotropic condition they usually creep along the 
bottom. When I introduced a large number of Polygordius 
larve into a eudiometer tube filled with sea-water, and set 
it in a vertical position in a dark room, the larvee were not 
distributed equally in the tube after some time—in about 
twenty-four hours—but one collection was usually found at 
the surface of the water, and a second at the bottom. If the 
tube was now carefully and suddenly brought to the light, 
all the larve at the surface layer showed themselves to be 
positively heliotropic, while all the larvee at the bottom were 
negatively heliotropic. Jt could further be easily shown 
that positively heliotropic Polygordius larvee went to the 
surface of the tube when put into the dark room, while 
negatively heliotropic Polygordius larve went to the bottom. 
Further, positively heliotropic Polygordius larvee may, as 
has already been mentioned, be made negatively heliotropic 
by warming. When a eudiometer tube containing Polygor- 
dius larvee at its surface was warmed in a dark room, the 
larvee went to the bottom of the tube. When the tube was 
cooled in the dark room, below 7° C., all the larve left the 
bottom and collected at the surface. Both the ascent and 
the descent of the larve are brought about by active swim- 
ming motions. It seems to me probable that the animal is 
not only heliotropic, but also geotropic, and that the sense 
of geotropism is always changed under the samie conditions 
as the sense of heliotropism. Negative geotropism is asso- 
ciated with positive heliotropism, and positive geotropism 
with negative heliotropism. Nevertheless, this difference 
persists, that the positively heliotropic animals (which at the 
same time are negatively geotropic) always swim, while the 
negatively heliotropic animals (which are also positively geo- 
tropic) lie or creep upon the bottom, and, it seems to me, 
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