no 



'Journal of Comparative Neurology atjd Psychology. 



all phototactic under others. Davenport ('97, p. 188) proved 

 certain species of Amoeba to be negative to light, and it is well 

 known that Stentor coeruleus responds very definitely to stimula- 

 tion by light. It is said that the Chytridium swarm spores have 

 an orange colored oil globule at the base of the flagellum which 

 may function as an eye-spot, but in the four organisms mentioned 

 last there are no structures which appear as though they could 

 take the place of these organs. It is, therefore, evident that we 

 have organisms without eye-spots which are sensitive to light but 

 as far as I know there are none with these structures that are not 

 sensitive. 



4. Wager ('00, PI. 32, Fig. 2) represents the flagellum in 

 Euglena viridis as indirectly connected with 

 the eye-spot, in that it has an enlargement 

 which lies immediately over the concave 

 surface of this structure as represented in 

 Fig. 4. The eye-spot is supposed to absorb 

 the blue of the spectrum and in some way 

 to stimulate the enlargement on the fla- 



c.v 



gellum. 



Fig. 4. Side view of ante- 

 rior end of Euglena viridis, after 

 Wager; e, eye-spot; /, flagel- 

 lum; e.f., enlargement in flagel- 

 lum; C.V., contractile vacuole. 



5. The fact that the eye-spots are larger 

 and more highly colored at the anterior 

 end of Volvox than at the posterior, that 

 they lose their color and become smaller 

 in the absence of light, and that they are 

 situated near the distal end of projections 

 which become longer as one proceeds from 

 the anterior end toward the posterior, and thus expose the eye- 

 spots to more light, indicates that these structures function in 

 light reactions. 



In view of the evidences presented above in favor of considering 

 the eye-spot as a light recipient organ, and in view of the fact that 

 there is nothing in the structure or location which indicates that 

 it could not function in light reactions or that it has any other 

 function, it appears safe to conclude that Ehrenberg's idea with 

 reference to the function of the eye-spot is correct. 



Wager ('00) suggests three ways in which the eye-spot in 

 Euglena viridis may function in light reactions : (i) It may absorb 

 light and thus produce a change in the movement of the flagellum; 

 (2) it may merely prevent the light rays from reaching one side of 



