THE REACTIONS OF RANATRA TO LIGHT. 

 By S. J. Holmes. 



Contributions from the Zoological Laboratory of the University of Michigan, No.ioo. 



With Six Figures in the Text. 



CONTENTS. 



I. Introduction. 

 II. General Habits. 



III. Reactions to Light. 



I — General features of the phototactic response. 



2 — The negative reaction. 



3 — Head and swaying movements in negative phototaxis. 



4 — The eftect of contact on phototaxis. 



5 — The effect of temperature on phototaxis. 



6 — Phototaxis leading to fatal results. 



7 — Inhibition of phototaxis by other activities. 



8 — The effect of hemisecting the brain. 



9 — The effect of covering the anterior half of the eyes. 

 10 — The effect of covering the posterior half of the eyes. 

 II — The effect of destroying or covering one eye. 



12 — Reactions of specimens with only a small part of the lateral sur- 

 face of one eye exposed. 

 13 — Phototaxis as modified by experience and habit. 

 14 — Formation of habits of turning. 



IV. General Considerations on the Phototactic Response. 



I. Introdtction. 



In endeavoring to ascertain the way in which animals of 

 various kinds orient themselves to the rays of light I have ex- 

 perimented with quite a large number of species in the hope of 

 finding forms in which the exact mode of response would reveal 

 itself. Animals vary greatly as regards both the definiteness 

 of their reactions to light and the ease with which their move- 

 ments can be followed. Among creatures of small size such as. 

 the Copepoda, Cladocera and Ostracoda, it is almost impossible 



