TABLE OF CONTENTS Vll 



CHAPTER VI 



Observations on Unicellular Forms' in the Process of Attaining 

 AND Retaining a Definite Axial Position with Reference to 

 THE Source of Light (continued) 



PAGE 



1. Stentor coeruleus 113 



a. Introduction; b. Orienting reactions; c. Difference in 

 sensitiveness with different surfaces illuminated; d. Lo- 

 calized stimulation; e. Summary. 



2. OeJjgonium Swarm-spores 123 



a. Description; b. Material; c. Locomotion; d. Orienta- 

 tion in Kght. 



3. Trachelomonas 128 



4. Chlamydomonas alboviridis (Stein) 131 



5. Chlorogonium 134 



6. Paramecium i34 



CHAPTER VII 



The Factors Involved in the Process of Orientation in Colonial 



Forms 



1. Volvox globator and minor 136 



2. Pandorina and Eudorina 146 



a. Function of the eye-spots. 



CHAPTER VIII 



Observations on the Responses Involved in the Regulation of 

 Movement toward the Source of Light in Coelenterates 



1. Hydra viridis 149 



a. Historical review; b. Effect of light intensity on ac- 

 tivity; c. Orientation and locomotion; d. Reactions of 

 negative specimens; e. General conclusions. 



2. Eudendrium Planulae 159 



3. Eudendrium Hydranths 163 



4. Reactions of Medusae 164 



CHAPTER IX 



Regulation in the Direction of Movement with Reference to the 

 Source of Light in Vermes, Fly Larvae, and Echinoderms 



I. Arenicola cristata — Larvae 166 



a. Description; b. Locomotion; c. Orientation; d. Me- 

 chanics of orientation; e. Discussion; /. Orienting 

 stimulation; g. Summary. 



