184 STUDIES IN GENEKAL 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. 1 



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 



i W. PREYER, Mittheilungen aus der zoologischen. Station zu Neapel, Vol. VII, 

 p. 96. 



