REACTIONS OF BRANCHIPUS TO EXTERNAL STIMULI 231 



moving about than when at rest. The movement is wave-hke, 

 progressing from the posterior feet to the anterior. The swimming 

 seems to be accomplished by this motion and the bending of the 

 abdomen, the abdomen and telson together acting as a rudder. 

 The fact that the beating to and fro of the swimming feet has a 

 respiratory as well as a locomotor function was brought out in 

 a series of experiments performed in this laboratory, in which 

 the rapidity of the beats was shown to increase with the addition 

 of CO2 to the water until a certain limit was reached, when the 

 further addition of CO2 caused the oscillations to cease entirely. 



It was thought that by counting these vibrations in different 

 light intensities some quantitative data might be obtained, which 

 would aid in answering the question as to the kinetic effect of light 

 on the swimming appendages. Although the data obtained were 

 insufficient in quantity to be conclusive, nevertheless they seem 

 to indicate that the activitj^ of Branchipus increases with an in- 

 crease in the intensity of the light. 



For the purpose of counting the vibrations of the swimming 

 feet the glass aquarium was placed in the dark box directly under 

 the 12 c.p. light, and a heat screen was interposed between the 

 light and the aquarium. The heat screen consisted of a circular 

 glass dish filled to the depth of one inch with water, which was 

 frequently changed. Since the light was practically non-direc- 

 tive under these conditions, the animals swam about at random, 

 or lay quietly on the bottom of the aquarium. The vibrations of 

 the swimming feet in a given time could be easily counted. A 

 25 c.p. light was used next under similar conditions, and counts 

 were made as before. The next day the experiment was repeated 

 in the reverse order, the 25 c.p. light being used first. Since males 

 were found to react to the light somewhat more quickly than fe- 

 males, and since individuals in the process of moulting seemed 

 to be less responsive, the same individual was used during an 

 experiment with the two lights. The results are given in tables 

 1 and 2. 



