THE BIONOMICS OF CONVOLUTA ROSCOFFENSIS. 397 



tliemselves evenly tlirougliout the trongli. If the temperature 

 of the water at one end of the trougli is gradually raised from 

 18° C. to 30° C, no thermotropic movement occurs. At 35° C. 

 the animals begin to move toward the cooler end (negative 

 thermotropism). What appears to us to be particularly note- 

 worthy is the fact that a temperature of from 35° C. to 38° C. 

 is fatal to Couvoluta, aud consequently many animals die 

 before they have succeeded in escaping from the heated end. 

 That Convoluta is capable of enduring a high temperature 

 is shown by the fact that when the source of heat used in the 

 foi'egoing experiment is removed^ and the water allowed to 

 cool, Couvolutas which had massed themselves up at the 

 cooler end begin to invade the warmer end whilst the 

 temperature there is still 30° C, This movement may not, 

 however, be a positive thermotropism, but merely the ex- 

 pression of a tendency of masses of Convoluta to spread 

 themselves evenly when nob prevented from doing so by 

 unilateral light. Convoluta, then, is negatively thermoti'opic 

 only just below its death-point. It manifests attunement to 

 a high heat-intensity. 



3. Phototropis m. 



Previous observers have recorded the positive phototropism 

 of Convoluta. We have sought to determine the limits 

 within which this reaction occurs, and the influence which it 

 has upon habit. Positive phototropism is well marked in 

 light of medium intensity, but is not manifested in light of 

 low intensity. For example, it does not occur in a room 

 removed from direct light, although the light therein is high 

 enough to enable observations on the disposition of Con- 

 voluta to be made. Again, light may induce a negative 

 tropism. Thus a sudden reduction of illumination evokes a 

 sudden, though transitory, " negative " movement. This is 

 well shown in 1'ext-iig. 2, which represents an experiment 

 made for the purpose of determining the specific effects of 

 various parts of the spectrum. Series 2 of these figures 



