XX ILLUSTRATIONS 



100. Side view of anterior end of Eiiglena viridis 285 



101. Graphs showing the relation between the direction of loco- 



motion of flagellates observed in a field of light produced 

 by two horizontal beams crossing at right angles and that 

 demanded by the "Resultantengesetz" 288 



102. Curves representing the distribution in the spectrum of stim- 



ulating efficiency 289 



103. Camera drawings illustrating the response of Peranenia to 



contact or to rapid increase in luminous intensity . . . 291 



104. Graph showing the effect of dark-adaptation on sensitivity 



to light in Peranenia trkhophoruiu 292 



105. Graphs showing rate of light-adaptation in Peranenia . . 293 



106. Graphs showing relation between luminous intensity and re- 



action time, exposure period, latent period, and energy 



{for Peranema) 294 



107. Stentor coeruleus in the process of orientation 296 



108. Arrangement of zooids in a colony of Volvox 298 



109. Sketches showing the structure of the eyespot in Volvox and 



its action on light entering the pigment cup at different 

 angles 299 



110. Diagrammatic representation of the process of orientation 



in Volvox 301 



111. Sketches illustrating the effect of a galvanic current on a 



monopodal Amoeba moving toward the cathode . . . 307 



112. Sketches illustrating the effect of a galvanic current on mono- 



podal amoebae moving toward the anode in a weak cur- 

 rent 308 



113. Graphs showing comparative effect of different densities of 



current on the rate of locomotion 310 



114. A series of camera sketches of an Amoeba, showing the ef- 



fect of an alternating current 312 



115. Progressive cathodic reversal of the cilia and change of form 



in Paramecium as the constant electric current in made 

 stronger 322 



116. Paramecium showing reversal in the direction of the stroke 



of the cilia in a galvanic current 325 



117. Sketch showing in a stationary photopositive colony of Vol- 



