108 Papers from the Marine Biological Laboratory at Tortugas. 



the starfish come from a direction opposite to which the creature is mov- 

 ing. To the writer, it seems impossible that the rays reflected from the 

 extremely minute particles of india ink in the mixture have any directive 

 effect, since it has been found that the behavior is the same, i.e., the 

 starfish moves to the bright end of the field, whether the sun's rays enter 

 the prism as shown in the figure, whether they enter in the opposite 

 direction, or whether they enter vertically. 



EFFECT OF TEMPERATURE ON REACTION TO LIGHT. 



It has been shown above that Echiiiaster crassispina usually reacts 

 positively to brightly lighted regions, although occasionally the opposite 

 is found to be the case. Several investigators, including Loeb (1893), 

 Massart (1891), and Strasburger (1878), have stated that the sign of 

 reaction of some lower organisms is reversed when the temperature 

 changes from a certain degree to another. On the other hand, Parker 

 (1901), Yerkes (1903), and Mast (1907) find no change in the sign of 

 the reaction in the case of copepods, Daphnia pulex and Volvox globator. 



The writer tested the reaction to light of the starfish Echinaster 

 crassispina at different degrees of temperature. The apparatus used is 

 shown in figure 2. It w^as found that when the temperature of the water 

 w^as from 29° to 30° C. the reaction to light was at its optimum and that 

 the movement toward the most intensely lighted end of the dish was 

 very definite. A series of tests w^as made in which the temperature of 

 the water was graduall}^ decreased and also one in which it was gradu- 

 ally increased. The range of temperatures was as follows: 17.8°, 

 i8."4°, 20°, 21.1°, 21.7°, 22.2°, 24.4°, 25.6°, 26.7°, 28.9°, 29.5°, 32.7°, 

 33.3°, 34.4° C. As the temperature was reduced from 28.9° C. to 17.8° C. 

 the rate of movement toward the brighter end of the dish decreased 

 until locomotion was entirely inhibited at the latter degree. The 

 starfish settled down closely on the bottom of the dish and the tube 

 feet stuck so tightly to the glass that it was impossible to remove them 

 without tearing. This condition is exceptional for Echinaster crassispina 

 at ordinary temperatures. On the other hand, when the temperature 

 was increased from 28.9° C. to 34.4° C. the starfish did not adhere to the 

 dish, but its activity was very much reduced and although it continued 

 to react positively the movement was very slow. Above 34.4° C. the 

 starfish became almost lifeless. In no case was there any indication of 

 a reversal of the sign of reaction. The starfish continued to move from 

 the region of least intensity to that of greater intensity. 



Bohn (1908) describes an experiment which he considers as an ex- 

 ample of change in sign of "phototropisme." He placed an Asterina 

 gibbosa, which usually reacts negatively to bright light, in a lighted field. 

 The starfish began to move in a certain direction and was then turned 

 around through 180°; the result was that the specimen then moved in 

 the opposite direction. In other words, a starfish which reacted nega- 

 tively to bright light by moving away from it, reacted positively to 

 bright light by moving toward it when rotated through 180°. This 

 behavior Bohn interprets as a change in sign of "phototropisme." It 

 is true that Asterina changed its direction of movement with reference 

 to the more intensely lighted region, but this was undoubtedly not due 



