OBSERVATIONS OF THYONE BRIAREUS. 2/9 



the Other turned only three times in that direction. In other 

 words, twenty three out of thirty reactions {j'j per cent.) were 

 away from the hght. 



Another reaction which shows a negatively phototropic 

 response is apparent when an animal burrows next the side of a 

 glass vessel. It never remains against the glass but moves out 

 into the sand after it has covered itself. This action is without 

 doubt due to Hght stimulation for an animal will remain indefi- 

 nitely in contact with an opaque object, such as a stone. 



These reactions show that the Thyone is sensitive to decreased 

 light intensity, and that it is negatively phototropic but without 

 any definite orientation of the body to the source of the illumina- 

 tion, or the direction of the rays. This lack of orientation is 

 rather striking in a bilaterally symmetrical animal and it shows 

 that the response is not brought about in this case by unequal 

 stimulation on the right and left sides of the body. 



6. Heat Stimulation. — Thyone was not found to be very 

 responsive to temperature changes, and individuals lived for 

 several days at room temperature (24-28° C.) without apparent 

 injury. Attempts were made to induce reactions by local changes 

 in the temperature. The method was to siphon boiling water or 

 a mixture of ice and salt water through a small U-shaped glass 

 tube which could be brought close to the surface of the indi- 

 vidual to be tested. Although six different animals were each 

 tried twice with the hot tube and twice with the cold tube by 

 holding the tube less than a millimeter below the extended pos- 

 terior end, not a single response was observed. 



Attention was next turned to the effects of an increase or 

 decrease in temperature which affected the whole body. To test 

 the effect of increased temperature six individuals (which were 

 buried in the sand at the bottom of separate beakers containing 

 sea water) were placed two at a time on a sand-bath and slowly 

 heated. All the animals became active after the temperature 

 had reached 30° C. The tube-feet were waved about on all sides 

 and the body began to execute irregular twisting movements 

 which continued until the temperature was lowered again. Two 

 of the individuals were slowly heated to 36.5° C, the time 

 required to reach that temperature being one hour and thirteen 



