184 STUDIES IN GENERAL PHYSIOLOGY 
orientation of the animals, positive heliotropism must compel 
Asterina tenuispina to move to the surface of the water in 
the same way as negative geotropism does Asterina gibbosa. 
Since Asterina tenuispina is always positively heliotropic 
(and does not alter its heliotropic sense as do the nauplii of 
Balanus), periodic depth-migrations do not occur in it as 
they do in the nauplii of Balanus because of the change in 
the heliotropic sense of the latter. 
3. Preyer briefly mentions in his exhaustive work on the 
movements of starfish ‘the tendency of these animals to 
crawl upward” which he noticed in his observations on the 
climbing movements of starfish. Preyer writes as follows: 
The great tendency of starfish to move upward cannot be 
dependent upon lack of oxygen, lack of food, or changes in the 
temperature, or currents in the water, nor to a desire for light, for 
the upward movements occur also where these conditions are not 
at work. Some property of the bottom, or of that particular spot 
on the bottom upon which the animal rests, and which has become 
unfit for the attachment of the animal or its prolonged residence, 
probably compels the animal to climb upward. Yet parasites 
which I often found in the ambulacral feet of Luidia may also 
cause them to move upward, in so far as these stimuli may appear 
to the animal as originating from the horizontal bottom.! 
The first sentence in this generalization is incorrect, as 
light is indeed the factor which compels Asterina tenuispina 
to crawl upward. It is shown by the following experiment 
that the nature of the bottom upon which the animal rests 
does not compel it to move upward. If Asterina gibbosa is 
placed in a cubical box having glass sides, the animals leave 
the horizontal basal wall and climb up the vertical sides. If 
the box is turned through an angle of 90° about a horizontal 
axis, the animal leaves the wall, which has now become basal, 
and climbs up to, and remains upon, the wall which it left 
before when it lay horizontally. The character of the wall was 
1W. Preyer, Mittheilungen aus der zoologischen Station zu Neapel, Vol. VII, 
p. 96. 
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