REVERSIBILITY OF HELIOTROPISM OF ARENICOLA LARVAE. 



the same as described in the writer's previous paper. 1 The 

 free-swimming larvae, just after they leave the egg-strings at 

 the swarming stage, are strikingly positive to light. They are, 

 therefore, very favorable for work of this kind. 



The methods of experimentation were simple. At each trial, 

 four 100 c.c. beakers, one for control with normal sea-water at 

 room temperature, a second with a treated sea-water at room 

 temperature, a third with the same (treated) sea-water at higher 

 temperature, and a fourth with the same (treated) sea-water at 

 lower temperature, were used. Fifty c.c. of liquid were used in 

 each beaker. Each beaker was set in a larger vessel (finger bowl), 

 containing sea-water of the same temperature as the beaker. 

 When all the beakers were ready and fairly constant at the 

 desired temperatures, the larvae taken with a small pipette from 

 a very dense aggregation were distributed as uniformly as 

 possible in each beaker. 



Diffuse light came horizontally from one south window only. 

 Care was taken against reflected light by using folded black 

 cloth under the beakers and on a long board that was placed at 

 the north side of the dishes. 



III. EXPERIMENTAL. 



Recent discoveries in the reversing effect of temperature of 

 normal sea-water on the normal heliotropism of various animals 

 had made it desirable to examine this phenomenon in Arenicola 

 larvae and to see whether there is any temperature coefficient 

 when chemicals were added to it. In some experiments this 

 was fairly illustrated, as far as time-relation was concerned, but 

 others were not so successful as expected, possibly on account of 

 the entrance of other factors. 



i. Effects of Temperature. 



Mast states that he did not succeed in producing a reversal 

 of the positive heliotropism of Arenicola larvae by changing the 

 temperature of sea-water. 2 This was not the case in the writer's 

 experiments. Mast perhaps used old larvae instead of very 



1 Kanda, loc. cit. 



2 Mast, loc. cit. 



