REACTIONS OF BRANCHIPUS SERRATUS TO LIGHT, 

 HEAT AND GRAVITY 



MARY O. McGINNISi 



In the composite of activities which we call the habits of 

 Branchipus serratus, various reactions to external stimuli, such 

 as light, heat and gravity may be assumed to occur. The present 

 paper records a number of laboratory experiments designed to 

 test under controlled conditions certain of these reactions, and 

 thus obtain more information as to the roles played by the three 

 environmental factors in the daily life of the crustaceans. 



BEHAVIOR WITH RESPECT TO LIGHT 



Phototropisms ivith light of different intensities 



Several years ago while engaged in a laboratory study of this 

 species, the writer's attention was called to the great readiness 

 with which Branchipus reacted positively to light areas of consider- 

 able difference in intensity. When kept in a glass aquarium in 

 diffuse light there was only a slight tendency on the part of the ani- 

 mals to collect on the side next the source of light; but when a 

 screen was erected between one-half of the aquarium and the light, 

 in such a way as to make a light portion and a shaded portion, the 

 animals swarmed out from the t-haded area into the light one. If 

 two screens were set up, making two shaded portions with a light 

 streak between them, the animals collected in the light streak. 



A series of experiments was carried on in the spring of 1910 to 

 test this positive reaction under more carefully controlled condi- 



1 Contributions from the Zoological Laboratory, University of Illinois, under 

 the direction of Henry B. Ward, no. 5. 



THE JOURNAL OF EXPERIMENTAL ZOOLOQT, VOL. 10, NO. 2 



