124 LIGHT AND THE BEHAVIOR OF ORGANISMS 



unable to find any indication of an eye-spot in living speci- 

 mens although I spent much time in looking for it. Stras- 

 burger however claims to have observed a red pigment 

 spot after treatment with acetic acid. There is great varia- 

 tion in the size of the spores; some of those used in these 

 experiments were several times as large as others. I am 

 not certain, however, that they were all of the same species. 

 In general they are considerably smaller than Paramecia. 



Fig. 15. Oedogonium swarm-spores. In responding with the avoiding reac- 

 tion they always turn toward the same side. This side bears no definite relation 

 to any visible asymmetry in their structure. A turned toward the more concave 

 side, i.e., from the side near which the nucleus was located. B turned toward 

 the more convex side, near which the nucleus was found. C was very nearly sym- 

 metrical in form. It turned toward the side containing the nucleus. D, diagram 

 representing the direction of the stroke of the cilia during the process of turning. 

 This can be very distinctly seen under high magnification. 



b. Material. — Swarm-spores were obtained in great 

 numbers in midwinter by adding fresh water to a jar which 

 contained numerous Qildogonium filaments, and letting it 

 become slightly stale. In those jars which were in diffuse 

 sunlight the swarm-spores collected near the surface of 

 the water on the side facing the window. In those in 

 direct sunlight they usually collected on the opposite side. 

 They are quite strongly negative in their reactions to 

 gravity; this accounts for the collection near the surface 

 of the water. 



c. Locomotion. — ■ They swim on a spiral course of vary- 

 ing width and rotate on the long axis just as do Euglena 

 and Stentor. The smaller end is usually ahead but they 

 reverse freely, and under some conditions they swim with 

 the larger end ahead almost constantly. They rotate clock- 

 wise when the smaller end is ahead, but in the opposite 



