REACTIONS OF BRANCHIPUS TO EXTERNAL STIMULI 229 



Since certain investigators (Parker, '02; Juday, '04; and others) 

 have shown that some crustaceans are positive to weak Ught 

 while to hght of higher intensities they are negative, it seemed 

 that the same might be true of Branchipus. Accordingly they 

 were tested with all the different intensities available, 12, 25, and 

 280 candle powers. 



The 25 c.p. light was used in the same way as the 12 c.p. Ught 

 employed in the previous experiment. The same rectangular 

 glass aquarium was placed in the dark box, and the light changed 

 from end to end as before. The specimens responded positively 

 as with the weaker light. 



The 280 c.p. light was an arc lamp suspended in a dark room. 

 The aquarium was raised until it was on a level with the light as in 

 the previous experiments. Since the light could not be changed 

 from one side of the aquarium to the other, the latter was turned 

 around when the animals collected in the illuminated end. To 

 this arc light the animals were uniformly positive both in the 

 aquarium and in the pan with the cardboard cover containing the 

 square opening. 



From the results of these experiments, Branchipus may be 

 considered positively phototropic to lights varying in intensity 

 from 12 to 280 c.p. These results agree with those of Yerkes 

 ('01) for Daphnia, and of Carpenter ('05) for Drosophila. 



An interesting observation in connection with the above experi- 

 ments was made on the body orientation. Ordinarily, in an 

 aquarium or in ponds, Branchipus is seen swinuning with its 

 ventral side up ; but with the aquarium in the dark box, where we 

 can control the source and direction of the light, a different posi- 

 tion of the body may usually be observed. Wlien, with the light 

 at one end of the aquarium, an animal is dropped in at the darker 

 end, it immediately starts toward the light, with the ventral side 

 directed toward it, and the long axis of the body at right angles 

 to the hght rays. If the light is changed to the opposite side, 

 the animal turns and assumes the same orientation. If the light 

 is placed above or below a tall glass cylinder used as an aquarium, 

 Branchipus swims upward or downward, with the ventral side 

 always directed toward the light. It is only occasionally that an 



